diff --git a/lib/membership/custom_field.ex b/lib/membership/custom_field.ex
index 5b7514c..18b8154 100644
--- a/lib/membership/custom_field.ex
+++ b/lib/membership/custom_field.ex
@@ -12,7 +12,6 @@ defmodule Mv.Membership.CustomField do
   - `slug` - URL-friendly, immutable identifier automatically generated from name (e.g., "phone-mobile")
   - `value_type` - Data type constraint (`:string`, `:integer`, `:boolean`, `:date`, `:email`)
   - `description` - Optional human-readable description
-  - `immutable` - If true, custom field values cannot be changed after creation
   - `required` - If true, all members must have this custom field (future feature)
   - `show_in_overview` - If true, this custom field will be displayed in the member overview table and can be sorted
 
@@ -60,10 +59,10 @@ defmodule Mv.Membership.CustomField do
 
   actions do
     defaults [:read, :update]
-    default_accept [:name, :value_type, :description, :immutable, :required, :show_in_overview]
+    default_accept [:name, :value_type, :description, :required, :show_in_overview]
 
     create :create do
-      accept [:name, :value_type, :description, :immutable, :required, :show_in_overview]
+      accept [:name, :value_type, :description, :required, :show_in_overview]
       change Mv.Membership.CustomField.Changes.GenerateSlug
       validate string_length(:slug, min: 1)
     end
@@ -113,10 +112,6 @@ defmodule Mv.Membership.CustomField do
         trim?: true
       ]
 
-    attribute :immutable, :boolean,
-      default: false,
-      allow_nil?: false
-
     attribute :required, :boolean,
       default: false,
       allow_nil?: false
diff --git a/lib/mv/membership_fees/calendar_cycles.ex b/lib/mv/membership_fees/calendar_cycles.ex
new file mode 100644
index 0000000..8a4ef24
--- /dev/null
+++ b/lib/mv/membership_fees/calendar_cycles.ex
@@ -0,0 +1,329 @@
+defmodule Mv.MembershipFees.CalendarCycles do
+  @moduledoc """
+  Calendar-based cycle calculation functions for membership fees.
+
+  This module provides functions for calculating cycle boundaries
+  based on interval types (monthly, quarterly, half-yearly, yearly).
+
+  The calculation functions (`calculate_cycle_start/3`, `calculate_cycle_end/2`,
+  `next_cycle_start/2`) are pure functions with no side effects.
+
+  The time-dependent functions (`current_cycle?/3`, `last_completed_cycle?/3`)
+  depend on a date parameter for testability. Their 2-argument variants
+  (`current_cycle?/2`, `last_completed_cycle?/2`) use `Date.utc_today()` and
+  are not referentially transparent.
+
+  ## Interval Types
+
+  - `:monthly` - Cycles from 1st to last day of each month
+  - `:quarterly` - Cycles from 1st of Jan/Apr/Jul/Oct to last day of quarter
+  - `:half_yearly` - Cycles from 1st of Jan/Jul to last day of half-year
+  - `:yearly` - Cycles from Jan 1st to Dec 31st
+
+  ## Examples
+
+      iex> date = ~D[2024-03-15]
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(date, :monthly)
+      ~D[2024-03-01]
+
+      iex> cycle_start = ~D[2024-01-01]
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(cycle_start, :yearly)
+      ~D[2024-12-31]
+
+      iex> cycle_start = ~D[2024-01-01]
+      iex> Mv.MembershipFees.CalendarCycles.next_cycle_start(cycle_start, :yearly)
+      ~D[2025-01-01]
+  """
+
+  @typedoc """
+  Interval type for membership fee cycles.
+
+  - `:monthly` - Monthly cycles (1st to last day of month)
+  - `:quarterly` - Quarterly cycles (1st of quarter to last day of quarter)
+  - `:half_yearly` - Half-yearly cycles (1st of half-year to last day of half-year)
+  - `:yearly` - Yearly cycles (Jan 1st to Dec 31st)
+  """
+  @type interval :: :monthly | :quarterly | :half_yearly | :yearly
+
+  @doc """
+  Calculates the start date of the cycle that contains the reference date.
+
+  ## Parameters
+
+    - `date` - Ignored in this 3-argument version (kept for API consistency)
+    - `interval` - The interval type (`:monthly`, `:quarterly`, `:half_yearly`, `:yearly`)
+    - `reference_date` - The date used to determine which cycle to calculate
+
+  ## Returns
+
+    The start date of the cycle containing the reference date.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-03-15], :monthly, ~D[2024-05-20])
+      ~D[2024-05-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-03-15], :quarterly, ~D[2024-05-20])
+      ~D[2024-04-01]
+  """
+  @spec calculate_cycle_start(Date.t(), interval(), Date.t()) :: Date.t()
+  def calculate_cycle_start(_date, interval, reference_date) do
+    case interval do
+      :monthly -> monthly_cycle_start(reference_date)
+      :quarterly -> quarterly_cycle_start(reference_date)
+      :half_yearly -> half_yearly_cycle_start(reference_date)
+      :yearly -> yearly_cycle_start(reference_date)
+    end
+  end
+
+  @doc """
+  Calculates the start date of the cycle that contains the given date.
+
+  This is a convenience function that calls `calculate_cycle_start/3` with `date` as both
+  the input and reference date.
+
+  ## Parameters
+
+    - `date` - The date used to determine which cycle to calculate
+    - `interval` - The interval type (`:monthly`, `:quarterly`, `:half_yearly`, `:yearly`)
+
+  ## Returns
+
+    The start date of the cycle containing the given date.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-03-15], :monthly)
+      ~D[2024-03-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-05-15], :quarterly)
+      ~D[2024-04-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-09-15], :half_yearly)
+      ~D[2024-07-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_start(~D[2024-12-15], :yearly)
+      ~D[2024-01-01]
+  """
+  @spec calculate_cycle_start(Date.t(), interval()) :: Date.t()
+  def calculate_cycle_start(date, interval) do
+    calculate_cycle_start(date, interval, date)
+  end
+
+  @doc """
+  Calculates the end date of a cycle based on its start date and interval.
+
+  ## Parameters
+
+    - `cycle_start` - The start date of the cycle
+    - `interval` - The interval type
+
+  ## Returns
+
+    The end date of the cycle.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(~D[2024-03-01], :monthly)
+      ~D[2024-03-31]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(~D[2024-02-01], :monthly)
+      ~D[2024-02-29]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(~D[2024-01-01], :quarterly)
+      ~D[2024-03-31]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(~D[2024-01-01], :half_yearly)
+      ~D[2024-06-30]
+
+      iex> Mv.MembershipFees.CalendarCycles.calculate_cycle_end(~D[2024-01-01], :yearly)
+      ~D[2024-12-31]
+  """
+  @spec calculate_cycle_end(Date.t(), interval()) :: Date.t()
+  def calculate_cycle_end(cycle_start, interval) do
+    case interval do
+      :monthly -> monthly_cycle_end(cycle_start)
+      :quarterly -> quarterly_cycle_end(cycle_start)
+      :half_yearly -> half_yearly_cycle_end(cycle_start)
+      :yearly -> yearly_cycle_end(cycle_start)
+    end
+  end
+
+  @doc """
+  Calculates the start date of the next cycle.
+
+  ## Parameters
+
+    - `cycle_start` - The start date of the current cycle
+    - `interval` - The interval type
+
+  ## Returns
+
+    The start date of the next cycle.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.next_cycle_start(~D[2024-01-01], :monthly)
+      ~D[2024-02-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.next_cycle_start(~D[2024-01-01], :quarterly)
+      ~D[2024-04-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.next_cycle_start(~D[2024-01-01], :half_yearly)
+      ~D[2024-07-01]
+
+      iex> Mv.MembershipFees.CalendarCycles.next_cycle_start(~D[2024-01-01], :yearly)
+      ~D[2025-01-01]
+  """
+  @spec next_cycle_start(Date.t(), interval()) :: Date.t()
+  def next_cycle_start(cycle_start, interval) do
+    cycle_end = calculate_cycle_end(cycle_start, interval)
+    next_date = Date.add(cycle_end, 1)
+    calculate_cycle_start(next_date, interval)
+  end
+
+  @doc """
+  Checks if the cycle contains the given date.
+
+  ## Parameters
+
+    - `cycle_start` - The start date of the cycle
+    - `interval` - The interval type
+    - `today` - The date to check (defaults to today's date)
+
+  ## Returns
+
+    `true` if the given date is within the cycle, `false` otherwise.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.current_cycle?(~D[2024-03-01], :monthly, ~D[2024-03-15])
+      true
+
+      iex> Mv.MembershipFees.CalendarCycles.current_cycle?(~D[2024-02-01], :monthly, ~D[2024-03-15])
+      false
+
+      iex> Mv.MembershipFees.CalendarCycles.current_cycle?(~D[2024-03-01], :monthly, ~D[2024-03-01])
+      true
+
+      iex> Mv.MembershipFees.CalendarCycles.current_cycle?(~D[2024-03-01], :monthly, ~D[2024-03-31])
+      true
+  """
+  @spec current_cycle?(Date.t(), interval(), Date.t()) :: boolean()
+  def current_cycle?(cycle_start, interval, today) do
+    cycle_end = calculate_cycle_end(cycle_start, interval)
+
+    Date.compare(cycle_start, today) in [:lt, :eq] and
+      Date.compare(today, cycle_end) in [:lt, :eq]
+  end
+
+  @spec current_cycle?(Date.t(), interval()) :: boolean()
+  def current_cycle?(cycle_start, interval) do
+    current_cycle?(cycle_start, interval, Date.utc_today())
+  end
+
+  @doc """
+  Checks if the cycle is the last completed cycle.
+
+  A cycle is considered the last completed cycle if:
+  - The cycle has ended (cycle_end < today)
+  - The next cycle has not ended yet (today <= next_end)
+
+  In other words: `cycle_end < today <= next_end`
+
+  ## Parameters
+
+    - `cycle_start` - The start date of the cycle
+    - `interval` - The interval type
+    - `today` - The date to check against (defaults to today's date)
+
+  ## Returns
+
+    `true` if the cycle is the last completed cycle, `false` otherwise.
+
+  ## Examples
+
+      iex> Mv.MembershipFees.CalendarCycles.last_completed_cycle?(~D[2024-03-01], :monthly, ~D[2024-04-01])
+      true
+
+      iex> Mv.MembershipFees.CalendarCycles.last_completed_cycle?(~D[2024-03-01], :monthly, ~D[2024-03-15])
+      false
+
+      iex> Mv.MembershipFees.CalendarCycles.last_completed_cycle?(~D[2024-02-01], :monthly, ~D[2024-04-15])
+      false
+  """
+  @spec last_completed_cycle?(Date.t(), interval(), Date.t()) :: boolean()
+  def last_completed_cycle?(cycle_start, interval, today) do
+    cycle_end = calculate_cycle_end(cycle_start, interval)
+
+    # Cycle must have ended (cycle_end < today)
+    case Date.compare(today, cycle_end) do
+      :gt ->
+        # Check if this is the most recent completed cycle
+        # by verifying that the next cycle hasn't ended yet (today <= next_end)
+        next_start = next_cycle_start(cycle_start, interval)
+        next_end = calculate_cycle_end(next_start, interval)
+
+        Date.compare(today, next_end) in [:lt, :eq]
+
+      _ ->
+        false
+    end
+  end
+
+  @spec last_completed_cycle?(Date.t(), interval()) :: boolean()
+  def last_completed_cycle?(cycle_start, interval) do
+    last_completed_cycle?(cycle_start, interval, Date.utc_today())
+  end
+
+  # Private helper functions
+
+  defp monthly_cycle_start(date) do
+    Date.new!(date.year, date.month, 1)
+  end
+
+  defp monthly_cycle_end(cycle_start) do
+    Date.end_of_month(cycle_start)
+  end
+
+  defp quarterly_cycle_start(date) do
+    quarter_start_month =
+      case date.month do
+        m when m in [1, 2, 3] -> 1
+        m when m in [4, 5, 6] -> 4
+        m when m in [7, 8, 9] -> 7
+        m when m in [10, 11, 12] -> 10
+      end
+
+    Date.new!(date.year, quarter_start_month, 1)
+  end
+
+  defp quarterly_cycle_end(cycle_start) do
+    case cycle_start.month do
+      1 -> Date.new!(cycle_start.year, 3, 31)
+      4 -> Date.new!(cycle_start.year, 6, 30)
+      7 -> Date.new!(cycle_start.year, 9, 30)
+      10 -> Date.new!(cycle_start.year, 12, 31)
+    end
+  end
+
+  defp half_yearly_cycle_start(date) do
+    half_start_month = if date.month in 1..6, do: 1, else: 7
+    Date.new!(date.year, half_start_month, 1)
+  end
+
+  defp half_yearly_cycle_end(cycle_start) do
+    case cycle_start.month do
+      1 -> Date.new!(cycle_start.year, 6, 30)
+      7 -> Date.new!(cycle_start.year, 12, 31)
+    end
+  end
+
+  defp yearly_cycle_start(date) do
+    Date.new!(date.year, 1, 1)
+  end
+
+  defp yearly_cycle_end(cycle_start) do
+    Date.new!(cycle_start.year, 12, 31)
+  end
+end
diff --git a/lib/mv_web/components/core_components.ex b/lib/mv_web/components/core_components.ex
index a23381d..a1020ef 100644
--- a/lib/mv_web/components/core_components.ex
+++ b/lib/mv_web/components/core_components.ex
@@ -95,9 +95,11 @@ defmodule MvWeb.CoreComponents do
       <.button>Send!</.button>
       <.button phx-click="go" variant="primary">Send!</.button>
       <.button navigate={~p"/"}>Home</.button>
+      <.button disabled={true}>Disabled</.button>
   """
   attr :rest, :global, include: ~w(href navigate patch method)
   attr :variant, :string, values: ~w(primary)
+  attr :disabled, :boolean, default: false, doc: "Whether the button is disabled"
   slot :inner_block, required: true
 
   def button(%{rest: rest} = assigns) do
@@ -105,14 +107,37 @@ defmodule MvWeb.CoreComponents do
     assigns = assign(assigns, :class, Map.fetch!(variants, assigns[:variant]))
 
     if rest[:href] || rest[:navigate] || rest[:patch] do
+      # For links, we can't use disabled attribute, so we use btn-disabled class
+      # DaisyUI's btn-disabled provides the same styling as :disabled on buttons
+      link_class =
+        if assigns[:disabled],
+          do: ["btn", assigns.class, "btn-disabled"],
+          else: ["btn", assigns.class]
+
+      # Prevent interaction when disabled
+      # Remove navigation attributes to prevent "Open in new tab", "Copy link" etc.
+      link_attrs =
+        if assigns[:disabled] do
+          rest
+          |> Map.drop([:href, :navigate, :patch])
+          |> Map.merge(%{tabindex: "-1", "aria-disabled": "true"})
+        else
+          rest
+        end
+
+      assigns =
+        assigns
+        |> assign(:link_class, link_class)
+        |> assign(:link_attrs, link_attrs)
+
       ~H"""
-      <.link class={["btn", @class]} {@rest}>
+      <.link class={@link_class} {@link_attrs}>
         {render_slot(@inner_block)}
       </.link>
       """
     else
       ~H"""
-      <button class={["btn", @class]} {@rest}>
+      <button class={["btn", @class]} disabled={@disabled} {@rest}>
         {render_slot(@inner_block)}
       </button>
       """
diff --git a/lib/mv_web/components/layouts.ex b/lib/mv_web/components/layouts.ex
index 487a01f..86090a8 100644
--- a/lib/mv_web/components/layouts.ex
+++ b/lib/mv_web/components/layouts.ex
@@ -36,12 +36,16 @@ defmodule MvWeb.Layouts do
     default: nil,
     doc: "the current [scope](https://hexdocs.pm/phoenix/scopes.html)"
 
+  attr :club_name, :string,
+    default: nil,
+    doc: "optional club name to pass to navbar"
+
   slot :inner_block, required: true
 
   def app(assigns) do
     ~H"""
     <%= if @current_user do %>
-      <.navbar current_user={@current_user} />
+      <.navbar current_user={@current_user} club_name={@club_name} />
     <% end %>
     <main class="px-4 py-20 sm:px-6 lg:px-16">
       <div class="mx-auto max-full space-y-4">
diff --git a/lib/mv_web/components/layouts/navbar.ex b/lib/mv_web/components/layouts/navbar.ex
index 4246c99..1ff589b 100644
--- a/lib/mv_web/components/layouts/navbar.ex
+++ b/lib/mv_web/components/layouts/navbar.ex
@@ -12,15 +12,18 @@ defmodule MvWeb.Layouts.Navbar do
     required: true,
     doc: "The current user - navbar is only shown when user is present"
 
-  def navbar(assigns) do
-    club_name = get_club_name()
+  attr :club_name, :string,
+    default: nil,
+    doc: "Optional club name - if not provided, will be loaded from database"
 
+  def navbar(assigns) do
+    club_name = assigns[:club_name] || get_club_name()
     assigns = assign(assigns, :club_name, club_name)
 
     ~H"""
     <header class="navbar bg-base-100 shadow-sm">
       <div class="flex-1">
-        <a class="btn btn-ghost text-xl">{@club_name}</a>
+        <a href="/members" class="btn btn-ghost text-xl">{@club_name}</a>
         <ul class="menu menu-horizontal bg-base-200">
           <li><.link navigate="/members">{gettext("Members")}</.link></li>
           <li><.link navigate="/settings">{gettext("Settings")}</.link></li>
diff --git a/lib/mv_web/live/components/payment_filter_component.ex b/lib/mv_web/live/components/payment_filter_component.ex
index 47556dd..1ba9d8b 100644
--- a/lib/mv_web/live/components/payment_filter_component.ex
+++ b/lib/mv_web/live/components/payment_filter_component.ex
@@ -77,7 +77,7 @@ defmodule MvWeb.Components.PaymentFilterComponent do
             phx-target={@myself}
           >
             <.icon name="hero-users" class="h-4 w-4" />
-            {gettext("All")}
+            {gettext("All payment statuses")}
           </button>
         </li>
         <li role="none">
@@ -140,7 +140,7 @@ defmodule MvWeb.Components.PaymentFilterComponent do
   defp parse_filter(_), do: nil
 
   # Get display label for current filter
-  defp filter_label(nil), do: gettext("All")
+  defp filter_label(nil), do: gettext("All payment statuses")
   defp filter_label(:paid), do: gettext("Paid")
   defp filter_label(:not_paid), do: gettext("Not paid")
 end
diff --git a/lib/mv_web/live/custom_field_live/form_component.ex b/lib/mv_web/live/custom_field_live/form_component.ex
index 4fe8579..172cfd3 100644
--- a/lib/mv_web/live/custom_field_live/form_component.ex
+++ b/lib/mv_web/live/custom_field_live/form_component.ex
@@ -6,7 +6,7 @@ defmodule MvWeb.CustomFieldLive.FormComponent do
   - Create new custom field definitions
   - Edit existing custom fields
   - Select value type from supported types
-  - Set immutable and required flags
+  - Set required flag
   - Real-time validation
 
   ## Props
@@ -50,10 +50,10 @@ defmodule MvWeb.CustomFieldLive.FormComponent do
             label={gettext("Value type")}
             options={
               Ash.Resource.Info.attribute(Mv.Membership.CustomField, :value_type).constraints[:one_of]
+              |> Enum.map(fn type -> {MvWeb.Translations.FieldTypes.label(type), type} end)
             }
           />
           <.input field={@form[:description]} type="text" label={gettext("Description")} />
-          <.input field={@form[:immutable]} type="checkbox" label={gettext("Immutable")} />
           <.input field={@form[:required]} type="checkbox" label={gettext("Required")} />
           <.input
             field={@form[:show_in_overview]}
@@ -66,7 +66,7 @@ defmodule MvWeb.CustomFieldLive.FormComponent do
               {gettext("Cancel")}
             </.button>
             <.button phx-disable-with={gettext("Saving...")} variant="primary">
-              {gettext("Save Custom field")}
+              {gettext("Save Custom Field")}
             </.button>
           </div>
         </.form>
diff --git a/lib/mv_web/live/custom_field_live/index_component.ex b/lib/mv_web/live/custom_field_live/index_component.ex
index 8f63bf8..ccae3c6 100644
--- a/lib/mv_web/live/custom_field_live/index_component.ex
+++ b/lib/mv_web/live/custom_field_live/index_component.ex
@@ -5,7 +5,7 @@ defmodule MvWeb.CustomFieldLive.IndexComponent do
   ## Features
   - List all custom fields
   - Display type information (name, value type, description)
-  - Show immutable and required flags
+  - Show required flag
   - Create new custom fields
   - Edit existing custom fields
   - Delete custom fields with confirmation (cascades to all custom field values)
@@ -30,7 +30,7 @@ defmodule MvWeb.CustomFieldLive.IndexComponent do
               phx-click="new_custom_field"
               phx-target={@myself}
             >
-              <.icon name="hero-plus" /> {gettext("New Custom field")}
+              <.icon name="hero-plus" /> {gettext("New Custom Field")}
             </.button>
           </div>
         </div>
diff --git a/lib/mv_web/live/custom_field_value_live/form.ex b/lib/mv_web/live/custom_field_value_live/form.ex
index 4a7b02d..9663927 100644
--- a/lib/mv_web/live/custom_field_value_live/form.ex
+++ b/lib/mv_web/live/custom_field_value_live/form.ex
@@ -72,7 +72,7 @@ defmodule MvWeb.CustomFieldValueLive.Form do
         <% end %>
 
         <.button phx-disable-with={gettext("Saving...")} variant="primary">
-          {gettext("Save Custom field value")}
+          {gettext("Save Custom Field Value")}
         </.button>
         <.button navigate={return_path(@return_to, @custom_field_value)}>{gettext("Cancel")}</.button>
       </.form>
diff --git a/lib/mv_web/live/global_settings_live.ex b/lib/mv_web/live/global_settings_live.ex
index 0b3ec1c..9bce04b 100644
--- a/lib/mv_web/live/global_settings_live.ex
+++ b/lib/mv_web/live/global_settings_live.ex
@@ -37,7 +37,7 @@ defmodule MvWeb.GlobalSettingsLive do
   @impl true
   def render(assigns) do
     ~H"""
-    <Layouts.app flash={@flash} current_user={@current_user}>
+    <Layouts.app flash={@flash} current_user={@current_user} club_name={@settings.club_name}>
       <.header>
         {gettext("Settings")}
         <:subtitle>
@@ -80,10 +80,13 @@ defmodule MvWeb.GlobalSettingsLive do
   @impl true
   def handle_event("save", %{"setting" => setting_params}, socket) do
     case AshPhoenix.Form.submit(socket.assigns.form, params: setting_params) do
-      {:ok, updated_settings} ->
+      {:ok, _updated_settings} ->
+        # Reload settings from database to ensure all dependent data is updated
+        {:ok, fresh_settings} = Membership.get_settings()
+
         socket =
           socket
-          |> assign(:settings, updated_settings)
+          |> assign(:settings, fresh_settings)
           |> put_flash(:info, gettext("Settings updated successfully"))
           |> assign_form()
 
diff --git a/lib/mv_web/live/member_live/index.ex b/lib/mv_web/live/member_live/index.ex
index 8857298..25c23f9 100644
--- a/lib/mv_web/live/member_live/index.ex
+++ b/lib/mv_web/live/member_live/index.ex
@@ -145,7 +145,10 @@ defmodule MvWeb.MemberLive.Index do
         MapSet.put(socket.assigns.selected_members, id)
       end
 
-    {:noreply, assign(socket, :selected_members, selected)}
+    {:noreply,
+     socket
+     |> assign(:selected_members, selected)
+     |> update_selection_assigns()}
   end
 
   @impl true
@@ -159,7 +162,10 @@ defmodule MvWeb.MemberLive.Index do
         all_ids
       end
 
-    {:noreply, assign(socket, :selected_members, selected)}
+    {:noreply,
+     socket
+     |> assign(:selected_members, selected)
+     |> update_selection_assigns()}
   end
 
   @impl true
@@ -238,6 +244,7 @@ defmodule MvWeb.MemberLive.Index do
       socket
       |> assign(:query, q)
       |> load_members()
+      |> update_selection_assigns()
 
     existing_field_query = socket.assigns.sort_field
     existing_sort_query = socket.assigns.sort_order
@@ -263,6 +270,7 @@ defmodule MvWeb.MemberLive.Index do
       socket
       |> assign(:paid_filter, filter)
       |> load_members()
+      |> update_selection_assigns()
 
     # Build the URL with all params including new filter
     query_params =
@@ -309,6 +317,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
       |> push_field_selection_url()
 
     {:noreply, socket}
@@ -338,6 +347,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
       |> push_field_selection_url()
 
     {:noreply, socket}
@@ -389,6 +399,7 @@ defmodule MvWeb.MemberLive.Index do
       |> assign(:visible_custom_field_ids, extract_custom_field_ids(visible_custom_fields))
       |> load_members()
       |> prepare_dynamic_cols()
+      |> update_selection_assigns()
 
     {:noreply, socket}
   end
@@ -1112,4 +1123,34 @@ defmodule MvWeb.MemberLive.Index do
 
   # Public helper function to format dates for use in templates
   def format_date(date), do: DateFormatter.format_date(date)
+
+  # Updates selection-related assigns (selected_count, any_selected?, mailto_bcc)
+  # to avoid recalculating Enum.any? and Enum.count multiple times in templates.
+  #
+  # Note: Mailto URLs have length limits that vary by email client.
+  # For large selections, consider using export functionality instead.
+  defp update_selection_assigns(socket) do
+    members = socket.assigns.members
+    selected_members = socket.assigns.selected_members
+
+    selected_count =
+      Enum.count(members, &MapSet.member?(selected_members, &1.id))
+
+    any_selected? =
+      Enum.any?(members, &MapSet.member?(selected_members, &1.id))
+
+    mailto_bcc =
+      if any_selected? do
+        format_selected_member_emails(members, selected_members)
+        |> Enum.join(", ")
+        |> URI.encode_www_form()
+      else
+        ""
+      end
+
+    socket
+    |> assign(:selected_count, selected_count)
+    |> assign(:any_selected?, any_selected?)
+    |> assign(:mailto_bcc, mailto_bcc)
+  end
 end
diff --git a/lib/mv_web/live/member_live/index.html.heex b/lib/mv_web/live/member_live/index.html.heex
index fbeb416..13c4367 100644
--- a/lib/mv_web/live/member_live/index.html.heex
+++ b/lib/mv_web/live/member_live/index.html.heex
@@ -3,23 +3,21 @@
     {gettext("Members")}
     <:actions>
       <.button
-        :if={Enum.any?(@members, &MapSet.member?(@selected_members, &1.id))}
+        class="secondary"
         id="copy-emails-btn"
         phx-hook="CopyToClipboard"
         phx-click="copy_emails"
+        disabled={not @any_selected?}
         aria-label={gettext("Copy email addresses of selected members")}
       >
         <.icon name="hero-clipboard-document" />
-        {gettext("Copy emails")} ({Enum.count(@members, &MapSet.member?(@selected_members, &1.id))})
+        {gettext("Copy email addresses")} ({@selected_count})
       </.button>
       <.button
-        :if={Enum.any?(@members, &MapSet.member?(@selected_members, &1.id))}
-        href={
-          "mailto:?bcc=" <>
-          (MvWeb.MemberLive.Index.format_selected_member_emails(@members, @selected_members)
-           |> Enum.join(", ")
-           |> URI.encode())
-        }
+        class="secondary"
+        id="open-email-btn"
+        href={"mailto:?bcc=" <> @mailto_bcc}
+        disabled={not @any_selected?}
         aria-label={gettext("Open email program with BCC recipients")}
       >
         <.icon name="hero-envelope" />
diff --git a/mix.lock b/mix.lock
index 44dffbf..1dd3d48 100644
--- a/mix.lock
+++ b/mix.lock
@@ -26,7 +26,7 @@
   "esbuild": {:hex, :esbuild, "0.10.0", "b0aa3388a1c23e727c5a3e7427c932d89ee791746b0081bbe56103e9ef3d291f", [:mix], [{:jason, "~> 1.4", [hex: :jason, repo: "hexpm", optional: false]}], "hexpm", "468489cda427b974a7cc9f03ace55368a83e1a7be12fba7e30969af78e5f8c70"},
   "ets": {:hex, :ets, "0.9.0", "79c6a6c205436780486f72d84230c6cba2f8a9920456750ddd1e47389107d5fd", [:mix], [], "hexpm", "2861fdfb04bcaeff370f1a5904eec864f0a56dcfebe5921ea9aadf2a481c822b"},
   "ex_phone_number": {:hex, :ex_phone_number, "0.4.8", "c1c5e6f0673822a2a7b439b43af7d3eb1a5c19ae582b772b8b8d12625dd51ec1", [:mix], [{:sweet_xml, "~> 0.7", [hex: :sweet_xml, repo: "hexpm", optional: false]}], "hexpm", "43e2357c6b8cfe556bcd417f4ce9aaef267a786e31a2938902daaa0d36f69757"},
-  "expo": {:hex, :expo, "1.1.1", "4202e1d2ca6e2b3b63e02f69cfe0a404f77702b041d02b58597c00992b601db5", [], [], "hexpm", "5fb308b9cb359ae200b7e23d37c76978673aa1b06e2b3075d814ce12c5811640"},
+  "expo": {:hex, :expo, "1.1.1", "4202e1d2ca6e2b3b63e02f69cfe0a404f77702b041d02b58597c00992b601db5", [:mix], [], "hexpm", "5fb308b9cb359ae200b7e23d37c76978673aa1b06e2b3075d814ce12c5811640"},
   "file_system": {:hex, :file_system, "1.1.1", "31864f4685b0148f25bd3fbef2b1228457c0c89024ad67f7a81a3ffbc0bbad3a", [:mix], [], "hexpm", "7a15ff97dfe526aeefb090a7a9d3d03aa907e100e262a0f8f7746b78f8f87a5d"},
   "finch": {:hex, :finch, "0.20.0", "5330aefb6b010f424dcbbc4615d914e9e3deae40095e73ab0c1bb0968933cadf", [:mix], [{:mime, "~> 1.0 or ~> 2.0", [hex: :mime, repo: "hexpm", optional: false]}, {:mint, "~> 1.6.2 or ~> 1.7", [hex: :mint, repo: "hexpm", optional: false]}, {:nimble_options, "~> 0.4 or ~> 1.0", [hex: :nimble_options, repo: "hexpm", optional: false]}, {:nimble_pool, "~> 1.1", [hex: :nimble_pool, repo: "hexpm", optional: false]}, {:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "2658131a74d051aabfcba936093c903b8e89da9a1b63e430bee62045fa9b2ee2"},
   "fine": {:hex, :fine, "0.1.4", "b19a89c1476c7c57afb5f9314aed5960b5bc95d5277de4cb5ee8e1d1616ce379", [:mix], [], "hexpm", "be3324cc454a42d80951cf6023b9954e9ff27c6daa255483b3e8d608670303f5"},
@@ -39,7 +39,7 @@
   "iterex": {:hex, :iterex, "0.1.2", "58f9b9b9a22a55cbfc7b5234a9c9c63eaac26d276b3db80936c0e1c60355a5a6", [:mix], [], "hexpm", "2e103b8bcc81757a9af121f6dc0df312c9a17220f302b1193ef720460d03029d"},
   "jason": {:hex, :jason, "1.4.4", "b9226785a9aa77b6857ca22832cffa5d5011a667207eb2a0ad56adb5db443b8a", [:mix], [{:decimal, "~> 1.0 or ~> 2.0", [hex: :decimal, repo: "hexpm", optional: true]}], "hexpm", "c5eb0cab91f094599f94d55bc63409236a8ec69a21a67814529e8d5f6cc90b3b"},
   "joken": {:hex, :joken, "2.6.2", "5daaf82259ca603af4f0b065475099ada1b2b849ff140ccd37f4b6828ca6892a", [:mix], [{:jose, "~> 1.11.10", [hex: :jose, repo: "hexpm", optional: false]}], "hexpm", "5134b5b0a6e37494e46dbf9e4dad53808e5e787904b7c73972651b51cce3d72b"},
-  "jose": {:hex, :jose, "1.11.12", "06e62b467b61d3726cbc19e9b5489f7549c37993de846dfb3ee8259f9ed208b3", [], [], "hexpm", "31e92b653e9210b696765cdd885437457de1add2a9011d92f8cf63e4641bab7b"},
+  "jose": {:hex, :jose, "1.11.12", "06e62b467b61d3726cbc19e9b5489f7549c37993de846dfb3ee8259f9ed208b3", [:mix, :rebar3], [], "hexpm", "31e92b653e9210b696765cdd885437457de1add2a9011d92f8cf63e4641bab7b"},
   "lazy_html": {:hex, :lazy_html, "0.1.8", "677a8642e644eef8de98f3040e2520d42d0f0f8bd6c5cd49db36504e34dffe91", [:make, :mix], [{:cc_precompiler, "~> 0.1", [hex: :cc_precompiler, repo: "hexpm", optional: false]}, {:elixir_make, "~> 0.9.0", [hex: :elixir_make, repo: "hexpm", optional: false]}, {:fine, "~> 0.1.0", [hex: :fine, repo: "hexpm", optional: false]}], "hexpm", "0d8167d930b704feb94b41414ca7f5779dff9bca7fcf619fcef18de138f08736"},
   "libgraph": {:hex, :libgraph, "0.16.0", "3936f3eca6ef826e08880230f806bfea13193e49bf153f93edcf0239d4fd1d07", [:mix], [], "hexpm", "41ca92240e8a4138c30a7e06466acc709b0cbb795c643e9e17174a178982d6bf"},
   "live_debugger": {:hex, :live_debugger, "0.5.0", "95e0f7727d61010f7e9053923fb2a9416904a7533c2dfb36120e7684cba4c0af", [:mix], [{:igniter, ">= 0.5.40 and < 1.0.0-0", [hex: :igniter, repo: "hexpm", optional: true]}, {:phoenix, "~> 1.7", [hex: :phoenix, repo: "hexpm", optional: false]}, {:phoenix_live_view, "~> 0.20.8 or ~> 1.0", [hex: :phoenix_live_view, repo: "hexpm", optional: false]}], "hexpm", "73ebe95118d22aa402675f677abd731cb16b136d1b6ae5f4010441fb50753b14"},
@@ -80,7 +80,7 @@
   "telemetry_metrics": {:hex, :telemetry_metrics, "1.1.0", "5bd5f3b5637e0abea0426b947e3ce5dd304f8b3bc6617039e2b5a008adc02f8f", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "e7b79e8ddfde70adb6db8a6623d1778ec66401f366e9a8f5dd0955c56bc8ce67"},
   "telemetry_poller": {:hex, :telemetry_poller, "1.3.0", "d5c46420126b5ac2d72bc6580fb4f537d35e851cc0f8dbd571acf6d6e10f5ec7", [:rebar3], [{:telemetry, "~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "51f18bed7128544a50f75897db9974436ea9bfba560420b646af27a9a9b35211"},
   "text_diff": {:hex, :text_diff, "0.1.0", "1caf3175e11a53a9a139bc9339bd607c47b9e376b073d4571c031913317fecaa", [:mix], [], "hexpm", "d1ffaaecab338e49357b6daa82e435f877e0649041ace7755583a0ea3362dbd7"},
-  "thousand_island": {:hex, :thousand_island, "1.4.2", "735fa783005d1703359bbd2d3a5a3a398075ba4456e5afe3c5b7cf4666303d36", [], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "1c7637f16558fc1c35746d5ee0e83b18b8e59e18d28affd1f2fa1645f8bc7473"},
+  "thousand_island": {:hex, :thousand_island, "1.4.2", "735fa783005d1703359bbd2d3a5a3a398075ba4456e5afe3c5b7cf4666303d36", [:mix], [{:telemetry, "~> 0.4 or ~> 1.0", [hex: :telemetry, repo: "hexpm", optional: false]}], "hexpm", "1c7637f16558fc1c35746d5ee0e83b18b8e59e18d28affd1f2fa1645f8bc7473"},
   "tidewave": {:hex, :tidewave, "0.5.2", "f549acffe9daeed8b6b547c232c60de987770da7f827f9b3300140dfc465b102", [:mix], [{:circular_buffer, "~> 0.4 or ~> 1.0", [hex: :circular_buffer, repo: "hexpm", optional: false]}, {:igniter, "~> 0.6", [hex: :igniter, repo: "hexpm", optional: true]}, {:jason, "~> 1.4", [hex: :jason, repo: "hexpm", optional: false]}, {:phoenix_live_reload, ">= 1.6.1", [hex: :phoenix_live_reload, repo: "hexpm", optional: true]}, {:plug, "~> 1.17", [hex: :plug, repo: "hexpm", optional: false]}, {:req, "~> 0.5", [hex: :req, repo: "hexpm", optional: false]}], "hexpm", "34ab3ffee7e402f05cd1eae68d0e77ed0e0d1925677971ef83634247553e8afd"},
   "unicode_util_compat": {:hex, :unicode_util_compat, "0.7.1", "a48703a25c170eedadca83b11e88985af08d35f37c6f664d6dcfb106a97782fc", [:rebar3], [], "hexpm", "b3a917854ce3ae233619744ad1e0102e05673136776fb2fa76234f3e03b23642"},
   "websock": {:hex, :websock, "0.5.3", "2f69a6ebe810328555b6fe5c831a851f485e303a7c8ce6c5f675abeb20ebdadc", [:mix], [], "hexpm", "6105453d7fac22c712ad66fab1d45abdf049868f253cf719b625151460b8b453"},
diff --git a/priv/gettext/de/LC_MESSAGES/default.po b/priv/gettext/de/LC_MESSAGES/default.po
index 25f685d..3a83ecf 100644
--- a/priv/gettext/de/LC_MESSAGES/default.po
+++ b/priv/gettext/de/LC_MESSAGES/default.po
@@ -282,11 +282,6 @@ msgstr "Benutzer*in bearbeiten"
 msgid "Enabled"
 msgstr "Aktiviert"
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Immutable"
-msgstr "Unveränderlich"
-
 #: lib/mv_web/components/layouts/navbar.ex
 #, elixir-autogen, elixir-format
 msgid "Logout"
@@ -612,16 +607,6 @@ msgstr "Benutzerdefinierter Feldwert erfolgreich %{action}"
 msgid "Please select a custom field first"
 msgstr "Bitte wähle zuerst ein Benutzerdefiniertes Feld"
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field"
-msgstr "Benutzerdefiniertes Feld speichern"
-
-#: lib/mv_web/live/custom_field_value_live/form.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field value"
-msgstr "Benutzerdefinierten Feldwert speichern"
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #: lib/mv_web/live/member_live/form.ex
 #: lib/mv_web/live/member_live/show.ex
@@ -760,11 +745,6 @@ msgstr[1] "%{count} E-Mail-Adressen in die Zwischenablage kopiert"
 msgid "Copy email addresses of selected members"
 msgstr "E-Mail-Adressen der ausgewählten Mitglieder kopieren"
 
-#: lib/mv_web/live/member_live/index.html.heex
-#, elixir-autogen, elixir-format
-msgid "Copy emails"
-msgstr "E-Mails kopieren"
-
 #: lib/mv_web/live/member_live/index.ex
 #, elixir-autogen, elixir-format
 msgid "No email addresses found"
@@ -796,7 +776,6 @@ msgid "This field cannot be empty"
 msgstr "Dieses Feld darf nicht leer bleiben"
 
 #: lib/mv_web/components/core_components.ex
-#: lib/mv_web/live/components/payment_filter_component.ex
 #, elixir-autogen, elixir-format
 msgid "All"
 msgstr "Alle"
@@ -1389,14 +1368,10 @@ msgid "Failed to delete custom field: %{error}"
 msgstr "Konnte Feld nicht löschen: %{error}"
 
 #: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format, fuzzy
-msgid "New Custom Field"
-msgstr "Benutzerdefiniertes Feld speichern"
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #, elixir-autogen, elixir-format, fuzzy
-msgid "New Custom field"
-msgstr "Benutzerdefiniertes Feld speichern"
+msgid "New Custom Field"
+msgstr "Neues Benutzerdefiniertes Feld"
 
 #: lib/mv_web/live/global_settings_live.ex
 #, elixir-autogen, elixir-format
@@ -1438,6 +1413,26 @@ msgstr "Textfeld"
 msgid "Yes/No-Selection"
 msgstr "Ja/Nein-Auswahl"
 
+#: lib/mv_web/live/components/payment_filter_component.ex
+#, elixir-autogen, elixir-format
+msgid "All payment statuses"
+msgstr "Jeder Zahlungs-Zustand"
+
+#: lib/mv_web/live/member_live/index.html.heex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Copy email addresses"
+msgstr "E-Mail-Adressen kopieren"
+
+#: lib/mv_web/live/custom_field_live/form_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Save Custom Field"
+msgstr "Benutzerdefiniertes Feld speichern"
+
+#: lib/mv_web/live/custom_field_value_live/form.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Save Custom Field Value"
+msgstr "Benutzerdefinierten Feldwert speichern"
+
 #~ #: lib/mv_web/live/custom_field_live/show.ex
 #~ #, elixir-autogen, elixir-format
 #~ msgid "Auto-generated identifier (immutable)"
@@ -1449,6 +1444,11 @@ msgstr "Ja/Nein-Auswahl"
 #~ msgid "Birth Date"
 #~ msgstr "Geburtsdatum"
 
+#~ #: lib/mv_web/live/member_live/index.html.heex
+#~ #, elixir-autogen, elixir-format
+#~ msgid "Copy emails"
+#~ msgstr "E-Mails kopieren"
+
 #~ #: lib/mv_web/live/member_live/form.ex
 #~ #: lib/mv_web/live/member_live/show.ex
 #~ #, elixir-autogen, elixir-format
@@ -1471,6 +1471,16 @@ msgstr "Ja/Nein-Auswahl"
 #~ msgid "Id"
 #~ msgstr "ID"
 
+#~ #: lib/mv_web/live/custom_field_live/form_component.ex
+#~ #, elixir-autogen, elixir-format
+#~ msgid "Immutable"
+#~ msgstr "Unveränderlich"
+
+#~ #: lib/mv_web/live/custom_field_live/index_component.ex
+#~ #, elixir-autogen, elixir-format, fuzzy
+#~ msgid "New Custom field"
+#~ msgstr "Benutzerdefiniertes Feld speichern"
+
 #~ #: lib/mv_web/live/user_live/form.ex
 #~ #: lib/mv_web/live/user_live/show.ex
 #~ #, elixir-autogen, elixir-format
diff --git a/priv/gettext/default.pot b/priv/gettext/default.pot
index a7ab36b..8bb080e 100644
--- a/priv/gettext/default.pot
+++ b/priv/gettext/default.pot
@@ -283,11 +283,6 @@ msgstr ""
 msgid "Enabled"
 msgstr ""
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Immutable"
-msgstr ""
-
 #: lib/mv_web/components/layouts/navbar.ex
 #, elixir-autogen, elixir-format
 msgid "Logout"
@@ -613,16 +608,6 @@ msgstr ""
 msgid "Please select a custom field first"
 msgstr ""
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field"
-msgstr ""
-
-#: lib/mv_web/live/custom_field_value_live/form.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field value"
-msgstr ""
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #: lib/mv_web/live/member_live/form.ex
 #: lib/mv_web/live/member_live/show.ex
@@ -761,11 +746,6 @@ msgstr[1] ""
 msgid "Copy email addresses of selected members"
 msgstr ""
 
-#: lib/mv_web/live/member_live/index.html.heex
-#, elixir-autogen, elixir-format
-msgid "Copy emails"
-msgstr ""
-
 #: lib/mv_web/live/member_live/index.ex
 #, elixir-autogen, elixir-format
 msgid "No email addresses found"
@@ -797,7 +777,6 @@ msgid "This field cannot be empty"
 msgstr ""
 
 #: lib/mv_web/components/core_components.ex
-#: lib/mv_web/live/components/payment_filter_component.ex
 #, elixir-autogen, elixir-format
 msgid "All"
 msgstr ""
@@ -1390,13 +1369,9 @@ msgid "Failed to delete custom field: %{error}"
 msgstr ""
 
 #: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "New Custom Field"
-msgstr ""
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #, elixir-autogen, elixir-format
-msgid "New Custom field"
+msgid "New Custom Field"
 msgstr ""
 
 #: lib/mv_web/live/global_settings_live.ex
@@ -1438,3 +1413,23 @@ msgstr ""
 #, elixir-autogen, elixir-format
 msgid "Yes/No-Selection"
 msgstr ""
+
+#: lib/mv_web/live/components/payment_filter_component.ex
+#, elixir-autogen, elixir-format
+msgid "All payment statuses"
+msgstr ""
+
+#: lib/mv_web/live/member_live/index.html.heex
+#, elixir-autogen, elixir-format
+msgid "Copy email addresses"
+msgstr ""
+
+#: lib/mv_web/live/custom_field_live/form_component.ex
+#, elixir-autogen, elixir-format
+msgid "Save Custom Field"
+msgstr ""
+
+#: lib/mv_web/live/custom_field_value_live/form.ex
+#, elixir-autogen, elixir-format
+msgid "Save Custom Field Value"
+msgstr ""
diff --git a/priv/gettext/en/LC_MESSAGES/default.po b/priv/gettext/en/LC_MESSAGES/default.po
index e2a1876..e1c4cc0 100644
--- a/priv/gettext/en/LC_MESSAGES/default.po
+++ b/priv/gettext/en/LC_MESSAGES/default.po
@@ -283,11 +283,6 @@ msgstr ""
 msgid "Enabled"
 msgstr ""
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Immutable"
-msgstr ""
-
 #: lib/mv_web/components/layouts/navbar.ex
 #, elixir-autogen, elixir-format
 msgid "Logout"
@@ -613,16 +608,6 @@ msgstr ""
 msgid "Please select a custom field first"
 msgstr ""
 
-#: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field"
-msgstr ""
-
-#: lib/mv_web/live/custom_field_value_live/form.ex
-#, elixir-autogen, elixir-format
-msgid "Save Custom field value"
-msgstr ""
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #: lib/mv_web/live/member_live/form.ex
 #: lib/mv_web/live/member_live/show.ex
@@ -761,11 +746,6 @@ msgstr[1] ""
 msgid "Copy email addresses of selected members"
 msgstr ""
 
-#: lib/mv_web/live/member_live/index.html.heex
-#, elixir-autogen, elixir-format
-msgid "Copy emails"
-msgstr ""
-
 #: lib/mv_web/live/member_live/index.ex
 #, elixir-autogen, elixir-format
 msgid "No email addresses found"
@@ -797,7 +777,6 @@ msgid "This field cannot be empty"
 msgstr ""
 
 #: lib/mv_web/components/core_components.ex
-#: lib/mv_web/live/components/payment_filter_component.ex
 #, elixir-autogen, elixir-format
 msgid "All"
 msgstr ""
@@ -1390,13 +1369,9 @@ msgid "Failed to delete custom field: %{error}"
 msgstr ""
 
 #: lib/mv_web/live/custom_field_live/form_component.ex
-#, elixir-autogen, elixir-format, fuzzy
-msgid "New Custom Field"
-msgstr ""
-
 #: lib/mv_web/live/custom_field_live/index_component.ex
 #, elixir-autogen, elixir-format, fuzzy
-msgid "New Custom field"
+msgid "New Custom Field"
 msgstr ""
 
 #: lib/mv_web/live/global_settings_live.ex
@@ -1439,6 +1414,26 @@ msgstr ""
 msgid "Yes/No-Selection"
 msgstr ""
 
+#: lib/mv_web/live/components/payment_filter_component.ex
+#, elixir-autogen, elixir-format
+msgid "All payment statuses"
+msgstr ""
+
+#: lib/mv_web/live/member_live/index.html.heex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Copy email addresses"
+msgstr ""
+
+#: lib/mv_web/live/custom_field_live/form_component.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Save Custom Field"
+msgstr ""
+
+#: lib/mv_web/live/custom_field_value_live/form.ex
+#, elixir-autogen, elixir-format, fuzzy
+msgid "Save Custom Field Value"
+msgstr ""
+
 #~ #: lib/mv_web/live/custom_field_live/show.ex
 #~ #, elixir-autogen, elixir-format
 #~ msgid "Auto-generated identifier (immutable)"
@@ -1450,6 +1445,11 @@ msgstr ""
 #~ msgid "Birth Date"
 #~ msgstr ""
 
+#~ #: lib/mv_web/live/member_live/index.html.heex
+#~ #, elixir-autogen, elixir-format
+#~ msgid "Copy emails"
+#~ msgstr ""
+
 #~ #: lib/mv_web/live/member_live/form.ex
 #~ #: lib/mv_web/live/member_live/show.ex
 #~ #, elixir-autogen, elixir-format
@@ -1471,6 +1471,16 @@ msgstr ""
 #~ msgid "Id"
 #~ msgstr ""
 
+#~ #: lib/mv_web/live/custom_field_live/form_component.ex
+#~ #, elixir-autogen, elixir-format
+#~ msgid "Immutable"
+#~ msgstr ""
+
+#~ #: lib/mv_web/live/custom_field_live/index_component.ex
+#~ #, elixir-autogen, elixir-format, fuzzy
+#~ msgid "New Custom field"
+#~ msgstr ""
+
 #~ #: lib/mv_web/live/user_live/show.ex
 #~ #, elixir-autogen, elixir-format, fuzzy
 #~ msgid "Not set"
diff --git a/priv/repo/migrations/20251211172549_remove_immutable_from_custom_fields.exs b/priv/repo/migrations/20251211172549_remove_immutable_from_custom_fields.exs
new file mode 100644
index 0000000..9d25d49
--- /dev/null
+++ b/priv/repo/migrations/20251211172549_remove_immutable_from_custom_fields.exs
@@ -0,0 +1,21 @@
+defmodule Mv.Repo.Migrations.RemoveImmutableFromCustomFields do
+  @moduledoc """
+  Removes the immutable column from custom_fields table.
+
+  The immutable field is no longer needed in the custom field definition.
+  """
+
+  use Ecto.Migration
+
+  def up do
+    alter table(:custom_fields) do
+      remove :immutable
+    end
+  end
+
+  def down do
+    alter table(:custom_fields) do
+      add :immutable, :boolean, null: false, default: false
+    end
+  end
+end
diff --git a/priv/repo/seeds.exs b/priv/repo/seeds.exs
index bec9006..10af66b 100644
--- a/priv/repo/seeds.exs
+++ b/priv/repo/seeds.exs
@@ -12,28 +12,24 @@ for attrs <- [
         name: "String Field",
         value_type: :string,
         description: "Example for a field of type string",
-        immutable: true,
         required: false
       },
       %{
         name: "Date Field",
         value_type: :date,
         description: "Example for a field of type date",
-        immutable: true,
         required: false
       },
       %{
         name: "Boolean Field",
         value_type: :boolean,
         description: "Example for a field of type boolean",
-        immutable: true,
         required: false
       },
       %{
         name: "Email Field",
         value_type: :email,
         description: "Example for a field of type email",
-        immutable: true,
         required: false
       },
       # Realistic custom fields
@@ -41,56 +37,48 @@ for attrs <- [
         name: "Membership Number",
         value_type: :string,
         description: "Unique membership identification number",
-        immutable: false,
         required: false
       },
       %{
         name: "Emergency Contact",
         value_type: :string,
         description: "Emergency contact person name and phone",
-        immutable: false,
         required: false
       },
       %{
         name: "T-Shirt Size",
         value_type: :string,
         description: "T-Shirt size for events (XS, S, M, L, XL, XXL)",
-        immutable: false,
         required: false
       },
       %{
         name: "Newsletter Subscription",
         value_type: :boolean,
         description: "Whether member wants to receive newsletter",
-        immutable: false,
         required: false
       },
       %{
         name: "Date of Last Medical Check",
         value_type: :date,
         description: "Date of last medical examination",
-        immutable: false,
         required: false
       },
       %{
         name: "Secondary Email",
         value_type: :email,
         description: "Alternative email address",
-        immutable: false,
         required: false
       },
       %{
         name: "Membership Type",
         value_type: :string,
         description: "Type of membership (e.g., Regular, Student, Senior)",
-        immutable: false,
         required: false
       },
       %{
         name: "Parking Permit",
         value_type: :boolean,
         description: "Whether member has parking permit",
-        immutable: false,
         required: false
       }
     ] do
diff --git a/test/mv/membership_fees/calendar_cycles_test.exs b/test/mv/membership_fees/calendar_cycles_test.exs
new file mode 100644
index 0000000..29fec48
--- /dev/null
+++ b/test/mv/membership_fees/calendar_cycles_test.exs
@@ -0,0 +1,181 @@
+defmodule Mv.MembershipFees.CalendarCyclesTest do
+  @moduledoc """
+  Tests for CalendarCycles module.
+  """
+  use ExUnit.Case, async: true
+
+  alias Mv.MembershipFees.CalendarCycles
+
+  doctest Mv.MembershipFees.CalendarCycles
+
+  describe "calculate_cycle_start/3" do
+    test "uses reference_date when provided" do
+      date = ~D[2024-03-15]
+      reference = ~D[2024-05-20]
+
+      assert CalendarCycles.calculate_cycle_start(date, :monthly, reference) == ~D[2024-05-01]
+      assert CalendarCycles.calculate_cycle_start(date, :quarterly, reference) == ~D[2024-04-01]
+    end
+  end
+
+  describe "current_cycle?/3" do
+    # Basic examples are covered by doctests
+
+    test "works for all interval types" do
+      today = ~D[2024-03-15]
+
+      for interval <- [:monthly, :quarterly, :half_yearly, :yearly] do
+        cycle_start = CalendarCycles.calculate_cycle_start(today, interval)
+        result = CalendarCycles.current_cycle?(cycle_start, interval, today)
+
+        assert result == true, "Expected current cycle for #{interval} with start #{cycle_start}"
+      end
+    end
+  end
+
+  describe "current_cycle?/2 wrapper" do
+    test "calls current_cycle?/3 with Date.utc_today()" do
+      today = Date.utc_today()
+      cycle_start = CalendarCycles.calculate_cycle_start(today, :monthly)
+
+      # This test verifies the wrapper works, but uses actual today
+      # The real testing happens in current_cycle?/3 tests above
+      result = CalendarCycles.current_cycle?(cycle_start, :monthly)
+
+      assert result == true
+    end
+  end
+
+  describe "last_completed_cycle?/3" do
+    # Basic examples are covered by doctests
+
+    test "returns false when next cycle has also ended" do
+      # Two cycles ago: cycle ended, but next cycle also ended
+      today = ~D[2024-05-15]
+      cycle_start = ~D[2024-03-01]
+      # Cycle ended 2024-03-31, next cycle ended 2024-04-30, today is 2024-05-15
+
+      assert CalendarCycles.last_completed_cycle?(cycle_start, :monthly, today) == false
+    end
+
+    test "works correctly for quarterly intervals" do
+      # Q1 2024 ended on 2024-03-31
+      # Q2 2024 ends on 2024-06-30
+      # Today is 2024-04-15 (after Q1 ended, before Q2 ended)
+      today = ~D[2024-04-15]
+      past_quarter_start = ~D[2024-01-01]
+
+      assert CalendarCycles.last_completed_cycle?(past_quarter_start, :quarterly, today) == true
+    end
+
+    test "returns false when cycle ended on the given date" do
+      # Cycle ends on today, so it's still current, not completed
+      today = ~D[2024-03-31]
+      cycle_start = ~D[2024-03-01]
+
+      assert CalendarCycles.last_completed_cycle?(cycle_start, :monthly, today) == false
+    end
+  end
+
+  describe "last_completed_cycle?/2 wrapper" do
+    test "calls last_completed_cycle?/3 with Date.utc_today()" do
+      today = Date.utc_today()
+      cycle_start = CalendarCycles.calculate_cycle_start(today, :monthly)
+
+      # This test verifies the wrapper works, but uses actual today
+      # The real testing happens in last_completed_cycle?/3 tests above
+      result = CalendarCycles.last_completed_cycle?(cycle_start, :monthly)
+
+      # Result depends on actual today, so we just verify it's a boolean
+      assert is_boolean(result)
+    end
+  end
+
+  describe "edge cases" do
+    test "leap year: February has 29 days" do
+      # 2024 is a leap year
+      assert CalendarCycles.calculate_cycle_end(~D[2024-02-01], :monthly) == ~D[2024-02-29]
+
+      # 2023 is not a leap year
+      assert CalendarCycles.calculate_cycle_end(~D[2023-02-01], :monthly) == ~D[2023-02-28]
+    end
+
+    test "year boundary: December 31 to January 1" do
+      # Yearly cycle
+      assert CalendarCycles.next_cycle_start(~D[2024-01-01], :yearly) == ~D[2025-01-01]
+
+      # Monthly cycle across year boundary
+      assert CalendarCycles.next_cycle_start(~D[2024-12-01], :monthly) == ~D[2025-01-01]
+
+      # Half-yearly cycle across year boundary
+      assert CalendarCycles.next_cycle_start(~D[2024-07-01], :half_yearly) == ~D[2025-01-01]
+
+      # Quarterly cycle across year boundary
+      assert CalendarCycles.next_cycle_start(~D[2024-10-01], :quarterly) == ~D[2025-01-01]
+    end
+
+    test "month boundary: different month lengths" do
+      # 31-day months
+      assert CalendarCycles.calculate_cycle_end(~D[2024-01-01], :monthly) == ~D[2024-01-31]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-03-01], :monthly) == ~D[2024-03-31]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-05-01], :monthly) == ~D[2024-05-31]
+
+      # 30-day months
+      assert CalendarCycles.calculate_cycle_end(~D[2024-04-01], :monthly) == ~D[2024-04-30]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-06-01], :monthly) == ~D[2024-06-30]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-09-01], :monthly) == ~D[2024-09-30]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-11-01], :monthly) == ~D[2024-11-30]
+    end
+
+    test "date in middle of cycle: all functions work correctly" do
+      middle_date = ~D[2024-03-15]
+
+      # calculate_cycle_start
+      assert CalendarCycles.calculate_cycle_start(middle_date, :monthly) == ~D[2024-03-01]
+      assert CalendarCycles.calculate_cycle_start(middle_date, :quarterly) == ~D[2024-01-01]
+      assert CalendarCycles.calculate_cycle_start(middle_date, :half_yearly) == ~D[2024-01-01]
+      assert CalendarCycles.calculate_cycle_start(middle_date, :yearly) == ~D[2024-01-01]
+
+      # calculate_cycle_end
+      monthly_start = CalendarCycles.calculate_cycle_start(middle_date, :monthly)
+      assert CalendarCycles.calculate_cycle_end(monthly_start, :monthly) == ~D[2024-03-31]
+
+      # next_cycle_start
+      assert CalendarCycles.next_cycle_start(monthly_start, :monthly) == ~D[2024-04-01]
+    end
+
+    test "quarterly: all quarter boundaries correct" do
+      # Q1 boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-01-15], :quarterly) == ~D[2024-01-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-01-01], :quarterly) == ~D[2024-03-31]
+
+      # Q2 boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-05-15], :quarterly) == ~D[2024-04-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-04-01], :quarterly) == ~D[2024-06-30]
+
+      # Q3 boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-08-15], :quarterly) == ~D[2024-07-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-07-01], :quarterly) == ~D[2024-09-30]
+
+      # Q4 boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-11-15], :quarterly) == ~D[2024-10-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-10-01], :quarterly) == ~D[2024-12-31]
+    end
+
+    test "half_yearly: both half boundaries correct" do
+      # First half boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-03-15], :half_yearly) == ~D[2024-01-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-01-01], :half_yearly) == ~D[2024-06-30]
+
+      # Second half boundaries
+      assert CalendarCycles.calculate_cycle_start(~D[2024-09-15], :half_yearly) == ~D[2024-07-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-07-01], :half_yearly) == ~D[2024-12-31]
+    end
+
+    test "yearly: full year boundaries" do
+      assert CalendarCycles.calculate_cycle_start(~D[2024-06-15], :yearly) == ~D[2024-01-01]
+      assert CalendarCycles.calculate_cycle_end(~D[2024-01-01], :yearly) == ~D[2024-12-31]
+      assert CalendarCycles.next_cycle_start(~D[2024-01-01], :yearly) == ~D[2025-01-01]
+    end
+  end
+end
diff --git a/test/mv_web/member_live/index_custom_fields_accessibility_test.exs b/test/mv_web/member_live/index_custom_fields_accessibility_test.exs
index cfe3145..149d441 100644
--- a/test/mv_web/member_live/index_custom_fields_accessibility_test.exs
+++ b/test/mv_web/member_live/index_custom_fields_accessibility_test.exs
@@ -52,14 +52,11 @@ defmodule MvWeb.MemberLive.IndexCustomFieldsAccessibilityTest do
     field: field
   } do
     conn = conn_with_oidc_user(conn)
-    {:ok, _view, html} = live(conn, "/members")
+    {:ok, view, _html} = live(conn, "/members")
 
-    # Check that the sort button has aria-label
-    assert html =~ ~r/aria-label=["']Click to sort["']/i or
-             html =~ ~r/aria-label=["'].*sort.*["']/i
-
-    # Check that data-testid is present for testing
-    assert html =~ ~r/data-testid=["']custom_field_#{field.id}["']/
+    # Check that the sort button has aria-label and data-testid
+    test_id = "custom_field_#{field.id}"
+    assert has_element?(view, "[data-testid='#{test_id}'][aria-label='Click to sort']")
   end
 
   test "sort header component shows correct ARIA label when sorted ascending", %{
@@ -71,10 +68,9 @@ defmodule MvWeb.MemberLive.IndexCustomFieldsAccessibilityTest do
     {:ok, view, _html} =
       live(conn, "/members?query=&sort_field=custom_field_#{field.id}&sort_order=asc")
 
-    html = render(view)
-
-    # Check that aria-label indicates ascending sort
-    assert html =~ ~r/aria-label=["'].*ascending.*["']/i
+    # Check that aria-label indicates ascending sort using data-testid
+    test_id = "custom_field_#{field.id}"
+    assert has_element?(view, "[data-testid='#{test_id}'][aria-label='ascending']")
   end
 
   test "sort header component shows correct ARIA label when sorted descending", %{
@@ -86,21 +82,21 @@ defmodule MvWeb.MemberLive.IndexCustomFieldsAccessibilityTest do
     {:ok, view, _html} =
       live(conn, "/members?query=&sort_field=custom_field_#{field.id}&sort_order=desc")
 
-    html = render(view)
-
-    # Check that aria-label indicates descending sort
-    assert html =~ ~r/aria-label=["'].*descending.*["']/i
+    # Check that aria-label indicates descending sort using data-testid
+    test_id = "custom_field_#{field.id}"
+    assert has_element?(view, "[data-testid='#{test_id}'][aria-label='descending']")
   end
 
   test "custom field column header is keyboard accessible", %{conn: conn, field: field} do
     conn = conn_with_oidc_user(conn)
-    {:ok, _view, html} = live(conn, "/members")
+    {:ok, view, _html} = live(conn, "/members")
 
     # Check that the sort button is a button element (keyboard accessible)
-    assert html =~ ~r/<button[^>]*data-testid=["']custom_field_#{field.id}["']/
+    test_id = "custom_field_#{field.id}"
+    assert has_element?(view, "button[data-testid='#{test_id}']")
 
     # Button should not have tabindex="-1" (which would remove from tab order)
-    refute html =~ ~r/tabindex=["']-1["']/
+    refute has_element?(view, "button[data-testid='#{test_id}'][tabindex='-1']")
   end
 
   test "custom field column header has proper semantic structure", %{conn: conn, field: field} do
diff --git a/test/mv_web/member_live/index_test.exs b/test/mv_web/member_live/index_test.exs
index 30b61c7..3232cc0 100644
--- a/test/mv_web/member_live/index_test.exs
+++ b/test/mv_web/member_live/index_test.exs
@@ -410,15 +410,17 @@ defmodule MvWeb.MemberLive.IndexTest do
       assert render(view) =~ "1"
     end
 
-    test "copy button is not visible when no members are selected", %{conn: conn} do
+    test "copy button is disabled when no members selected", %{conn: conn} do
       conn = conn_with_oidc_user(conn)
       {:ok, view, _html} = live(conn, "/members")
 
-      # Ensure no members are selected (default state)
-      refute has_element?(view, "#copy-emails-btn")
+      # Copy button should be disabled (button element)
+      assert has_element?(view, "#copy-emails-btn[disabled]")
+      # Open email button should be disabled (link with tabindex and aria-disabled)
+      assert has_element?(view, "#open-email-btn[tabindex='-1'][aria-disabled='true']")
     end
 
-    test "copy button is visible when members are selected", %{
+    test "copy button is enabled after selection", %{
       conn: conn,
       member1: member1
     } do
@@ -428,8 +430,13 @@ defmodule MvWeb.MemberLive.IndexTest do
       # Select a member by sending the select_member event directly
       render_click(view, "select_member", %{"id" => member1.id})
 
-      # Button should now be visible
-      assert has_element?(view, "#copy-emails-btn")
+      # Copy button should now be enabled (no disabled attribute)
+      refute has_element?(view, "#copy-emails-btn[disabled]")
+      # Open email button should now be enabled (no tabindex=-1 or aria-disabled)
+      refute has_element?(view, "#open-email-btn[tabindex='-1']")
+      refute has_element?(view, "#open-email-btn[aria-disabled='true']")
+      # Counter should show correct count
+      assert render(view) =~ "1"
     end
 
     test "copy button click triggers event and shows flash", %{