diff --git a/app/models/spree/calculator/default_tax.rb b/app/models/spree/calculator/default_tax.rb
index bfacafddef..87ea942067 100644
--- a/app/models/spree/calculator/default_tax.rb
+++ b/app/models/spree/calculator/default_tax.rb
@@ -1,4 +1,7 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
+require 'open_food_network/enterprise_fee_calculator'
 
 module Spree
   module Calculator
@@ -19,19 +22,40 @@ module Spree
       private
 
       def rate
-        self.calculable
+        calculable
       end
 
+      # Enable calculation of tax for enterprise fees with tax rates where included_in_price = false
       def compute_order(order)
         matched_line_items = order.line_items.select do |line_item|
-          line_item.tax_category == rate.tax_category
+          line_item.product.tax_category == rate.tax_category
         end
 
         line_items_total = matched_line_items.sum(&:total)
-        if rate.included_in_price
-          deduced_total_by_rate(line_items_total, rate)
-        else
-          round_to_two_places(line_items_total * rate.amount)
+
+        # Added this line
+        calculator = OpenFoodNetwork::EnterpriseFeeCalculator.new(order.distributor, order.order_cycle)
+
+        # Added this block, finds relevant fees for each line_item, calculates the tax on them, and returns the total tax
+        per_item_fees_total = order.line_items.sum do |line_item|
+          calculator.per_item_enterprise_fee_applicators_for(line_item.variant)
+            .select { |applicator|
+              (!applicator.enterprise_fee.inherits_tax_category && applicator.enterprise_fee.tax_category == rate.tax_category) ||
+                (applicator.enterprise_fee.inherits_tax_category && line_item.product.tax_category == rate.tax_category)
+            }
+            .sum { |applicator| applicator.enterprise_fee.compute_amount(line_item) }
+        end
+
+        # Added this block, finds relevant fees for whole order, calculates the tax on them, and returns the total tax
+        per_order_fees_total = calculator.per_order_enterprise_fee_applicators_for(order)
+          .select { |applicator| applicator.enterprise_fee.tax_category == rate.tax_category }
+          .sum { |applicator| applicator.enterprise_fee.compute_amount(order) }
+
+        # round_to_two_places(line_items_total * rate.amount) # Removed this line
+
+        # Added this block
+        [line_items_total, per_item_fees_total, per_order_fees_total].sum do |total|
+          round_to_two_places(total * rate.amount)
         end
       end
 
diff --git a/app/models/spree/calculator/default_tax_decorator.rb b/app/models/spree/calculator/default_tax_decorator.rb
deleted file mode 100644
index ccc73abb9f..0000000000
--- a/app/models/spree/calculator/default_tax_decorator.rb
+++ /dev/null
@@ -1,40 +0,0 @@
-require 'open_food_network/enterprise_fee_calculator'
-
-Spree::Calculator::DefaultTax.class_eval do
-  private
-
-  # Override this method to enable calculation of tax for
-  # enterprise fees with tax rates where included_in_price = false
-  def compute_order(order)
-    matched_line_items = order.line_items.select do |line_item|
-      line_item.product.tax_category == rate.tax_category
-    end
-
-    line_items_total = matched_line_items.sum(&:total)
-
-    # Added this line
-    calculator = OpenFoodNetwork::EnterpriseFeeCalculator.new(order.distributor, order.order_cycle)
-
-    # Added this block, finds relevant fees for each line_item, calculates the tax on them, and returns the total tax
-    per_item_fees_total = order.line_items.sum do |line_item|
-      calculator.per_item_enterprise_fee_applicators_for(line_item.variant)
-        .select { |applicator|
-          (!applicator.enterprise_fee.inherits_tax_category && applicator.enterprise_fee.tax_category == rate.tax_category) ||
-            (applicator.enterprise_fee.inherits_tax_category && line_item.product.tax_category == rate.tax_category)
-        }
-        .sum { |applicator| applicator.enterprise_fee.compute_amount(line_item) }
-    end
-
-    # Added this block, finds relevant fees for whole order, calculates the tax on them, and returns the total tax
-    per_order_fees_total = calculator.per_order_enterprise_fee_applicators_for(order)
-      .select { |applicator| applicator.enterprise_fee.tax_category == rate.tax_category }
-      .sum { |applicator| applicator.enterprise_fee.compute_amount(order) }
-
-    # round_to_two_places(line_items_total * rate.amount) # Removed this line
-
-    # Added this block
-    [line_items_total, per_item_fees_total, per_order_fees_total].sum do |total|
-      round_to_two_places(total * rate.amount)
-    end
-  end
-end
diff --git a/app/models/spree/calculator/flat_percent_item_total.rb b/app/models/spree/calculator/flat_percent_item_total.rb
index 8b897397e4..0d2dc7e0db 100644
--- a/app/models/spree/calculator/flat_percent_item_total.rb
+++ b/app/models/spree/calculator/flat_percent_item_total.rb
@@ -1,19 +1,24 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
+require 'spree/localized_number'
 
 module Spree
   module Calculator
     class FlatPercentItemTotal < Calculator
+      extend Spree::LocalizedNumber
+
       preference :flat_percent, :decimal, default: 0
 
+      localize_number :preferred_flat_percent
+
       def self.description
         Spree.t(:flat_percent)
       end
 
       def compute(object)
-        return unless object.present? && object.respond_to?(:item_total)
-
-        item_total = object.item_total
-        value = item_total * BigDecimal(self.preferred_flat_percent.to_s) / 100.0
+        item_total = line_items_for(object).map(&:amount).sum
+        value = item_total * BigDecimal(preferred_flat_percent.to_s) / 100.0
         (value * 100).round.to_f / 100
       end
     end
diff --git a/app/models/spree/calculator/flat_percent_item_total_decorator.rb b/app/models/spree/calculator/flat_percent_item_total_decorator.rb
deleted file mode 100644
index ae95f59ca2..0000000000
--- a/app/models/spree/calculator/flat_percent_item_total_decorator.rb
+++ /dev/null
@@ -1,15 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Calculator::FlatPercentItemTotal.class_eval do
-    extend Spree::LocalizedNumber
-
-    localize_number :preferred_flat_percent
-
-    def compute(object)
-      item_total = line_items_for(object).map(&:amount).sum
-      value = item_total * BigDecimal(preferred_flat_percent.to_s) / 100.0
-      (value * 100).round.to_f / 100
-    end
-  end
-end
diff --git a/app/models/spree/calculator/flat_rate.rb b/app/models/spree/calculator/flat_rate.rb
index 3cfb94dd4c..a2d6d9c55b 100644
--- a/app/models/spree/calculator/flat_rate.rb
+++ b/app/models/spree/calculator/flat_rate.rb
@@ -1,17 +1,24 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
+require 'spree/localized_number'
 
 module Spree
   module Calculator
     class FlatRate < Calculator
+      extend Spree::LocalizedNumber
+
       preference :amount, :decimal, default: 0
       preference :currency, :string, default: Spree::Config[:currency]
 
+      localize_number :preferred_amount
+
       def self.description
-        Spree.t(:flat_rate_per_order)
+        I18n.t(:flat_rate_per_order)
       end
 
-      def compute(object=nil)
-        self.preferred_amount
+      def compute(_object = nil)
+        preferred_amount
       end
     end
   end
diff --git a/app/models/spree/calculator/flat_rate_decorator.rb b/app/models/spree/calculator/flat_rate_decorator.rb
deleted file mode 100644
index d7abe3cf1b..0000000000
--- a/app/models/spree/calculator/flat_rate_decorator.rb
+++ /dev/null
@@ -1,13 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Calculator::FlatRate.class_eval do
-    extend Spree::LocalizedNumber
-
-    localize_number :preferred_amount
-
-    def self.description
-      I18n.t(:flat_rate_per_order)
-    end
-  end
-end
diff --git a/app/models/spree/calculator/flexi_rate.rb b/app/models/spree/calculator/flexi_rate.rb
index 9e8f16cc00..fe80c45883 100644
--- a/app/models/spree/calculator/flexi_rate.rb
+++ b/app/models/spree/calculator/flexi_rate.rb
@@ -1,30 +1,39 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
+require 'spree/localized_number'
 
 module Spree
   module Calculator
     class FlexiRate < Calculator
+      extend Spree::LocalizedNumber
+
       preference :first_item,      :decimal, default: 0.0
       preference :additional_item, :decimal, default: 0.0
       preference :max_items,       :integer, default: 0
       preference :currency,        :string,  default: Spree::Config[:currency]
 
+      localize_number :preferred_first_item,
+                      :preferred_additional_item
+
       def self.description
-        Spree.t(:flexible_rate)
+        I18n.t(:flexible_rate)
       end
 
-      def self.available?(object)
+      def self.available?(_object)
         true
       end
 
       def compute(object)
         sum = 0
-        max = self.preferred_max_items.to_i
-        items_count = object.line_items.map(&:quantity).sum
-        items_count.times do |i|
-          if i == 0
-            sum += self.preferred_first_item.to_f
-          elsif ((max > 0) && (i <= (max - 1))) || (max == 0)
-            sum += self.preferred_additional_item.to_f
+        max = preferred_max_items.to_i
+        items_count = line_items_for(object).map(&:quantity).sum
+        # check max value to avoid divide by 0 errors
+        unless max == 0
+          if items_count > max
+            sum += (max - 1) * preferred_additional_item.to_f + preferred_first_item.to_f
+          elsif items_count <= max
+            sum += (items_count - 1) * preferred_additional_item.to_f + preferred_first_item.to_f
           end
         end
 
diff --git a/app/models/spree/calculator/flexi_rate_decorator.rb b/app/models/spree/calculator/flexi_rate_decorator.rb
deleted file mode 100644
index de112f4f0b..0000000000
--- a/app/models/spree/calculator/flexi_rate_decorator.rb
+++ /dev/null
@@ -1,30 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Calculator::FlexiRate.class_eval do
-    extend Spree::LocalizedNumber
-
-    localize_number :preferred_first_item,
-                    :preferred_additional_item
-
-    def self.description
-      I18n.t(:flexible_rate)
-    end
-
-    def compute(object)
-      sum = 0
-      max = preferred_max_items.to_i
-      items_count = line_items_for(object).map(&:quantity).sum
-      # check max value to avoid divide by 0 errors
-      unless max == 0
-        if items_count > max
-          sum += (max - 1) * preferred_additional_item.to_f + preferred_first_item.to_f
-        elsif items_count <= max
-          sum += (items_count - 1) * preferred_additional_item.to_f + preferred_first_item.to_f
-        end
-      end
-
-      sum
-    end
-  end
-end
diff --git a/app/models/spree/calculator/per_item.rb b/app/models/spree/calculator/per_item.rb
index a2ce2f4348..10c7965c0d 100644
--- a/app/models/spree/calculator/per_item.rb
+++ b/app/models/spree/calculator/per_item.rb
@@ -1,25 +1,34 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
+require 'spree/localized_number'
 
 module Spree
   module Calculator
     class PerItem < Calculator
+      extend Spree::LocalizedNumber
+
       preference :amount, :decimal, default: 0
       preference :currency, :string, default: Spree::Config[:currency]
 
+      localize_number :preferred_amount
+
       def self.description
-        Spree.t(:flat_rate_per_item)
+        I18n.t(:flat_rate_per_item)
       end
 
-      def compute(object=nil)
+      def compute(object = nil)
         return 0 if object.nil?
-        self.preferred_amount * object.line_items.reduce(0) do |sum, value|
-          if matching_products.blank? || matching_products.include?(value.product)
-            value_to_add = value.quantity
-          else
-            value_to_add = 0
-          end
+
+        number_of_line_items = line_items_for(object).reduce(0) do |sum, line_item|
+          value_to_add = if matching_products.blank? || matching_products.include?(line_item.product)
+                           line_item.quantity
+                         else
+                           0
+                         end
           sum + value_to_add
         end
+        preferred_amount * number_of_line_items
       end
 
       # Returns all products that match this calculator, but only if the calculator
diff --git a/app/models/spree/calculator/per_item_decorator.rb b/app/models/spree/calculator/per_item_decorator.rb
deleted file mode 100644
index e385ad8bf8..0000000000
--- a/app/models/spree/calculator/per_item_decorator.rb
+++ /dev/null
@@ -1,27 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Calculator::PerItem.class_eval do
-    extend Spree::LocalizedNumber
-
-    localize_number :preferred_amount
-
-    def self.description
-      I18n.t(:flat_rate_per_item)
-    end
-
-    def compute(object = nil)
-      return 0 if object.nil?
-
-      number_of_line_items = line_items_for(object).reduce(0) do |sum, line_item|
-        value_to_add = if matching_products.blank? || matching_products.include?(line_item.product)
-                         line_item.quantity
-                       else
-                         0
-                       end
-        sum + value_to_add
-      end
-      preferred_amount * number_of_line_items
-    end
-  end
-end
diff --git a/app/models/spree/calculator/price_sack.rb b/app/models/spree/calculator/price_sack.rb
index d3a05e0229..ac6bf0b653 100644
--- a/app/models/spree/calculator/price_sack.rb
+++ b/app/models/spree/calculator/price_sack.rb
@@ -1,32 +1,39 @@
+# frozen_string_literal: false
+
 require_dependency 'spree/calculator'
 # For #to_d method on Ruby 1.8
 require 'bigdecimal/util'
+require 'spree/localized_number'
 
 module Spree
   module Calculator
     class PriceSack < Calculator
+      extend Spree::LocalizedNumber
+
       preference :minimal_amount, :decimal, default: 0
       preference :normal_amount, :decimal, default: 0
       preference :discount_amount, :decimal, default: 0
       preference :currency, :string, default: Spree::Config[:currency]
 
+      localize_number :preferred_minimal_amount,
+                      :preferred_normal_amount,
+                      :preferred_discount_amount
+
       def self.description
-        Spree.t(:price_sack)
+        I18n.t(:price_sack)
       end
 
-      # as object we always get line items, as calculable we have Coupon, ShippingMethod
       def compute(object)
-        if object.is_a?(Array)
-          base = object.map { |o| o.respond_to?(:amount) ? o.amount : BigDecimal(o.to_s) }.sum
-        else
-          base = object.respond_to?(:amount) ? object.amount : BigDecimal(object.to_s)
+        min = preferred_minimal_amount.to_f
+        order_amount = line_items_for(object).map { |x| x.price * x.quantity }.sum
+
+        if order_amount < min
+          cost = preferred_normal_amount.to_f
+        elsif order_amount >= min
+          cost = preferred_discount_amount.to_f
         end
 
-        if base < self.preferred_minimal_amount
-          self.preferred_normal_amount
-        else
-          self.preferred_discount_amount
-        end
+        cost
       end
     end
   end
diff --git a/app/models/spree/calculator/price_sack_decorator.rb b/app/models/spree/calculator/price_sack_decorator.rb
deleted file mode 100644
index 389649f916..0000000000
--- a/app/models/spree/calculator/price_sack_decorator.rb
+++ /dev/null
@@ -1,28 +0,0 @@
-require 'spree/localized_number'
-
-module Spree
-  Calculator::PriceSack.class_eval do
-    extend Spree::LocalizedNumber
-
-    localize_number :preferred_minimal_amount,
-                    :preferred_normal_amount,
-                    :preferred_discount_amount
-
-    def self.description
-      I18n.t(:price_sack)
-    end
-
-    def compute(object)
-      min = preferred_minimal_amount.to_f
-      order_amount = line_items_for(object).map { |x| x.price * x.quantity }.sum
-
-      if order_amount < min
-        cost = preferred_normal_amount.to_f
-      elsif order_amount >= min
-        cost = preferred_discount_amount.to_f
-      end
-
-      cost
-    end
-  end
-end