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Bug with tax calculation and discount price

Hello,

After reading a lot of threads about problem with tax calculation with discount price I found no solution about what is happening to me.

As you can see in the screenshot joined the price total after discount is different between the 3 products. This is a 30% discount on each products. The first and the last seems good but the second one has a different total. I don't know why. Thanks for your help !

EDIT :

Add a screenshot of my tax configuration settings

enter image description here

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2
  • Can you post a screenshot of your settings under system->configuration->tax settings?
    – simonthesorcerer
    Commented Jan 15, 2014 at 11:20
  • try and set Tax Calculation Method Based On to unit price instead of Total
    – Sander Mangel
    Commented Feb 18, 2014 at 21:24

2 Answers 2

Reset to default
1

Issue: The result of tax is a bit more than being expected when the tax setting is as follows in system->configuration->tax settings

Tax Calculation Method Based On: Unit Price
Apply Customer Tax: After Discount

Resolution: I rewrite the method _calcUnitTaxAmount in model Mage_Tax_Model_Sales_Total_Quote_Tax

It was:

$discountRate = ($unitTax/$price) * 100;<br/>
$baseDiscountRate = ($baseUnitTax/$basePrice) * 100;

After rewrite, it is

$discountRate = $inclTax == 1 ? ($unitTax/($price - $unitTax)) * 100 : ($unitTax/$price) * 100;<br/>
$baseDiscountRate = $inclTax == 1 ? ($baseUnitTax/($basePrice - $baseUnitTax)) * 100 : ($baseUnitTax/$basePrice) * 100;

Then the result in the totals is correct.

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4
  • can you please explain in term of tax have to be calculate in magento store
    – Ami Kamboj
    Commented Jun 2, 2014 at 10:12
  • 1
    The first level tax calculation is Tax Calculation Method Based On which includes CALC_UNIT_BASE, CALC_ROW_BASE, CALC_TOTAL_BASE. Then the process of calculation goes into seperately. <br/> In CALC_UNIT_BASE, it does another level calculation by Apply Customer Tax: Before Discount / After discount. The bugs happens in After discount.
    – Amier
    Commented Jun 2, 2014 at 10:21
  • you can also see the details and view point :magentocommerce.com/knowledge-base/entry/…
    – Ami Kamboj
    Commented Jun 2, 2014 at 10:27
  • Cool Thanks, It needs more time to figure the tax calculation out clearly.
    – Amier
    Commented Jun 2, 2014 at 10:35
0

In magento 1.8.1 are lots of rounding issues fixed (there are still a lot) so you should try making an update.

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