diff --git a/app/models/concerns/price_calculation.rb b/app/models/concerns/price_calculation.rb
index b73e43c6..03b9a7ad 100644
--- a/app/models/concerns/price_calculation.rb
+++ b/app/models/concerns/price_calculation.rb
@@ -4,11 +4,17 @@ module PriceCalculation
   # Gross price = net price + deposit + tax.
   # @return [Number] Gross price.
   def gross_price
-    ((price + deposit) * (tax / 100 + 1)).round(2)
+    add_percent(price + deposit, tax)
   end
 
   # @return [Number] Price for the foodcoop-member.
   def fc_price
-    (gross_price  * (FoodsoftConfig[:price_markup] / 100 + 1)).round(2)
+    add_percent(gross_price, FoodsoftConfig[:price_markup])
+  end
+
+  private
+
+  def add_percent(value, percent)
+    (value * (percent * 0.01 + 1)).round(2)
   end
 end
diff --git a/spec/app_config.yml b/spec/app_config.yml
index 0bf51d41..1bed23f6 100644
--- a/spec/app_config.yml
+++ b/spec/app_config.yml
@@ -13,8 +13,9 @@ default: &defaults
   # true by default to keep compat with older installations, but test with false here
   use_nick: false
 
+  price_markup: 5
+
   # do we really need the following ones?
-  price_markup: 5.0
   tax_default: 6.0
   email_sender: noreply@minimal.test