A client of us had a very annoying bug which we can't figure out. It involves discount and tax in the quote.

It happens when an item in the cart get discount applied. The discount will be applied as it should. But the tax of the discount is also given as a extra discount.


When ordering 2 items of 29,95 euro a discount of 4,95 euro is applied. This results in a total of 25 euro * 2 items. Including tax. this is correct. Normal calculation

When the cart is updated in any way for some reason the item price is now 24.14 euro. while the price and discount stay the same. After update

this is a difference of 0,86 euro. Which happens as follows:
4,95 euro discount is considered including tax (121%)
0,86 is the amount of tax on the discount 0,86 euro = (4,95 / 1.21) * 0.21

This tax should not be removed from the total price. But for some reason is removed. The total when proceeding is 48,28 euro including tax Totals wrong

The settings are to apply tax after discount. tax discount settings

What we have tried

  • Both coupons and pricerules apply
  • Customer group does not matter
  • Both the frontend and the backend have this problem.
  • The problem appeared when we updated from magento to
  • All prices are including tax
  • All settings are checked at all levels
  • Turn off all modules

Can anybody help me?

  • Ah, after 26 months I have faced the same issue, did you find the solution? – Adnan Sep 8 '18 at 1:08
  • I'm afraid I don't know anymore :( – janw Sep 10 '18 at 10:19

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