diff --git a/app/models/billable_period.rb b/app/models/billable_period.rb
index 79f4b3eaba..635a0b9a28 100644
--- a/app/models/billable_period.rb
+++ b/app/models/billable_period.rb
@@ -15,14 +15,16 @@ class BillablePeriod < ActiveRecord::Base
   end
 
   def bill
-    # Will make this more sophisicated in the future in that it will use global config variables to calculate
+    fixed = Spree::Config[:account_invoices_monthly_fixed]
+    rate = Spree::Config[:account_invoices_monthly_rate]
+    cap = Spree::Config[:account_invoices_monthly_cap]
+
     return 0 if trial?
-    if ['own', 'any'].include? sells
-      bill = (turnover * 0.02).round(2)
-      bill > 50 ? 50 : bill
-    else
-      0
-    end
+    return 0 unless ['own', 'any'].include?(sells)
+
+    bill = fixed + (turnover * rate).round(2)
+    return bill unless cap > 0
+    [bill, cap].min
   end
 
   def label
diff --git a/spec/models/billable_period_spec.rb b/spec/models/billable_period_spec.rb
index 1ad974d804..b53a0bc36b 100644
--- a/spec/models/billable_period_spec.rb
+++ b/spec/models/billable_period_spec.rb
@@ -1,15 +1,18 @@
 require 'spec_helper'
 
-describe Customer, type: :model do
+describe BillablePeriod, type: :model do
+
+  require 'spec_helper'
+
   describe 'ensure_correct_adjustment' do
     let!(:start_of_july) { Time.zone.now.beginning_of_year + 6.months }
     let!(:user) { create(:user) }
     let!(:invoice) { create(:order, user: user) }
-    let!(:billable_period) { create(:billable_period, owner: user, begins_at: start_of_july, ends_at: start_of_july + 12.days) }
+    let!(:subject) { create(:billable_period, owner: user, begins_at: start_of_july, ends_at: start_of_july + 12.days) }
 
     before do
-      allow(billable_period).to receive(:bill) { 99 }
-      allow(billable_period).to receive(:adjustment_label) { "Label for adjustment" }
+      allow(subject).to receive(:bill) { 99 }
+      allow(subject).to receive(:adjustment_label) { "Label for adjustment" }
       Spree::Config.set({ account_bill_inc_tax: true })
       Spree::Config.set({ account_bill_tax_rate: 0.1 })
     end
@@ -17,11 +20,101 @@ describe Customer, type: :model do
     context "when no adjustment currently exists" do
       it "creates an adjustment on the given order" do
         expect(invoice.total_tax).to eq 0.0
-        expect(billable_period.adjustment).to be nil
-        billable_period.ensure_correct_adjustment_for(invoice)
-        expect(billable_period.adjustment).to be_a Spree::Adjustment
+        expect(subject.adjustment).to be nil
+        subject.ensure_correct_adjustment_for(invoice)
+        expect(subject.adjustment).to be_a Spree::Adjustment
         expect(invoice.total_tax).to eq 9.0
       end
     end
   end
+
+
+  describe "calculating monthly bills for enterprises" do
+    let!(:subject) { create(:billable_period, turnover: 100) }
+
+    context "when a fixed cost is included" do
+      before { Spree::Config.set(:account_invoices_monthly_fixed, 10) }
+
+      context "when a percentage of turnover is included" do
+        before { Spree::Config.set(:account_invoices_monthly_rate, 0.5) }
+
+        context "when the bill is capped" do
+          context "at a level higher than the fixed charge plus the product of the rate and turnover" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 65) }
+            it { expect(subject.bill).to eq 60 }
+          end
+
+          context "at a level lower than the fixed charge plus the product of the rate and turnover" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 55) }
+            it { expect(subject.bill).to eq 55 }
+          end
+        end
+
+        context "when the bill is not capped" do
+          before { Spree::Config.set(:account_invoices_monthly_cap, 0) }
+          it { expect(subject.bill).to eq 60 }
+        end
+      end
+
+      context "when a percentage of turnover is not included" do
+        before { Spree::Config.set(:account_invoices_monthly_rate, 0) }
+
+        context "when the bill is capped" do
+          context "at a level higher than the fixed charge" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 15) }
+            it { expect(subject.bill).to eq 10 }
+          end
+
+          context "at a level lower than the fixed charge" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 5) }
+            it { expect(subject.bill).to eq 5 }
+          end
+        end
+
+        context "when the bill is not capped" do
+          before { Spree::Config.set(:account_invoices_monthly_cap, 0) }
+          it { expect(subject.bill).to eq 10 }
+        end
+      end
+    end
+
+    context "when a fixed cost is not included" do
+      before { Spree::Config.set(:account_invoices_monthly_fixed, 0) }
+
+      context "when a percentage of turnover is included" do
+        before { Spree::Config.set(:account_invoices_monthly_rate, 0.5) }
+
+        context "when the bill is capped" do
+          context "at a level higher than the product of the rate and turnover" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 55) }
+            it { expect(subject.bill).to eq 50 }
+          end
+
+          context "at a level lower than the product of the rate and turnover" do
+            before { Spree::Config.set(:account_invoices_monthly_cap, 45) }
+            it { expect(subject.bill).to eq 45 }
+          end
+        end
+
+        context "when the bill is not capped" do
+          before { Spree::Config.set(:account_invoices_monthly_cap, 0) }
+          it { expect(subject.bill).to eq 50 }
+        end
+      end
+
+      context "when a percentage of turnover is not included" do
+        before { Spree::Config.set(:account_invoices_monthly_rate, 0) }
+
+        context "when the bill is capped" do
+          before { Spree::Config.set(:account_invoices_monthly_cap, 20) }
+          it { expect(subject.bill).to eq 0 }
+        end
+
+        context "when the bill is not capped" do
+          before { Spree::Config.set(:account_invoices_monthly_cap, 0) }
+          it { expect(subject.bill).to eq 0 }
+        end
+      end
+    end
+  end
 end