I have had a long discussion with Chris at CT regarding VAT calculations on discounted orders.
In my example I have a product = £15 @ 20% VAT
£12.5 * 1.2 = £15 (£2.50 VAT included).
Now I want to give a £4 discount. As VAT is calculated on the discounted sale price my thinking is that the taxable total would be £15 - £4 = £11. VAT would therefore be £1.83.
Chris believes this is wrong and it can only be one of these two scenarios:
(12.5 - 4) * 1.2 That makes a total of 10.2. VAT of 1.70
(12.5 * 1.2) - 4 That makes a total of 11. VAT of 2.5
I think neither of those scenarios give the correct VAT amount although the equations do balance out.
In CT it is not clear whether the value you put in as the discount amount includes or excludes VAT and I think the percentage amount only appears to apply to the tax inc price but not the taxed amount itself? Having done a bit of research I think the calculations should be more along the lines of:
1) If the discount is a percentage, the percentage is applied to each component. So a 50% discount would be: £7.50 of which £1.25 is VAT = £12.50 (base) + £2.50 (vat) - £6.25 (base) - £1.25 (vat).
2) If the discount is a flat amount, it needs to have the VAT component reverse-calculated A £4 discount would be: £11 of which £1.83 is VAT = £12.50 (base) + £2.50 (vat) - (£3.33 (base) + £0.67 (vat)).
Where this gets more complicated are sales which include vattable and non vattable products (such as books) and whether the discount applies to an individual line item or the cart total as a whole.
Has anyone else had issues with VAT on discounts in CT and worked out a solution.. or is my logic completely wrong!!