We have a Magento store running 1.9 Community version.

We have a number of discount codes we publish in magazines, this morning we noticed however instead of giving a 10% discount it's giving a little bit more than it should...

Check this screenshot:


10% of £97.87 = £9.79 - no problem

£97.87 minus the discount rate £9.79 does not equal £86.12

This is the settings for the code: https://i.stack.imgur.com/vSxf1.png What are we doing wrong here? I am at a total loss.


2 Answers 2


Here's what happens:

  • You have 20% VAT.
  • Your discount is set to be calculated on price including VAT: 9.79
  • Your product price excluding VAT: 81.55
  • Your discount is set to apply at subtotal, subtotal is excluding VAT: 81.55 - 8.79 = 71.77
  • Grand total is subtotal after discount plus VAT: 71.77 * 1.20 = 86.12

So your fix is to calculate discount price excluding VAT or apply at subtotal including tax.


Maybe the discount it is subtracting adds some tax? There's a setting in config->sales->tax that says to calculate tax before or after discount and the setting below it specifies whether you calculate tax in the discount.

  • I've done the maths on this, it was also my first thought. It does not matter either way, the amount will be the same.
    – Ste Hughes
    Mar 4, 2015 at 15:26
  • They shouldn't be the same if you change the setting.. are you sure you are using the correct configuration scope?
    – Robin
    Mar 4, 2015 at 15:41
  • we have the same problem - choosing subtotal always uses excl tax
    – snh_nl
    Apr 26, 2017 at 12:10

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