diff --git a/app/models/invoice.rb b/app/models/invoice.rb
index 19e25d5c9..a5c3f3f85 100644
--- a/app/models/invoice.rb
+++ b/app/models/invoice.rb
@@ -34,7 +34,7 @@ class Invoice < ActiveRecord::Base
 
   before_create :set_invoice_number
   before_create :apply_default_vat_rate, unless: :vat_rate?
-  before_create :save_total
+  before_create :calculate_total, unless: :total?
 
   attribute :vat_rate, ::Type::VATRate.new
   attr_readonly :vat_rate
@@ -150,14 +150,18 @@ class Invoice < ActiveRecord::Base
   end
 
   def subtotal
-    (items.map(&:item_sum_without_vat).sum).round(2)
+    invoice_items.collect { |line_item| line_item.item_sum_without_vat }.reduce(:+)
   end
 
-  def vat
+  def vat_amount
     return 0 unless vat_rate
     subtotal * vat_rate / 100
   end
 
+  def total
+    calculate_total unless total?
+  end
+
   private
 
   def apply_default_vat_rate
@@ -165,6 +169,6 @@ class Invoice < ActiveRecord::Base
   end
 
   def calculate_total
-    # (sum_without_vat + vat).round(2)
+    self.total = subtotal + vat_amount
   end
 end
diff --git a/test/models/invoice_test.rb b/test/models/invoice_test.rb
index fb7e66821..9222f83b8 100644
--- a/test/models/invoice_test.rb
+++ b/test/models/invoice_test.rb
@@ -59,12 +59,12 @@ class InvoiceTest < ActiveSupport::TestCase
   end
 
   def test_calculates_vat_amount
-    assert_equal BigDecimal('1.5'), @invoice.vat
+    assert_equal BigDecimal('1.5'), @invoice.vat_amount
   end
 
   def test_vat_amount_is_zero_when_vat_rate_is_blank
     @invoice.vat_rate = nil
-    assert_equal 0, @invoice.vat
+    assert_equal 0, @invoice.vat_amount
   end
 
   def test_calculates_subtotal