Tax calculations for products with Specific prices set by percentage discount are wrong

[Jacek Es]

Hi,

PrestaShop v8.1.7

Tested on fresh installation

 

Settings:

Product base price: £0.30

Specific price by discount: -31% from 1000pcs

UK VAT @ 20%

Rounding mode: Round on each item

Rounding type: Round up away from zero, when it is half way there (recommended)

Currency decimal: 2

Free delivery

Quantity ordered: 1000 pcs

 

PrestaShop calculations:

Correct calculations should be:

Subtotal: £210.00

Total (VAT excl.): £210.00

Total (tax incl.): £252.00

 

Regards,

Jacek

 

 

[Nickz]

How do you set up the discount?

Per Group or generally?

[Jacek Es]

Discount is set at the product level for all groups:

 

Jacek

 

[Nickz]

did you set the - in front of the tax percentage?

[Jacek Es]

I don't see this option:

 

All the customers groups are set for Price display method: Tax excluded

 

I think the problem may be with the rounding. In my example when the base price is £0.30 and 31% discount is applied then it gives the discounted price of £0.207. When the currency is set to 2 Decimals the calculations are wrong. When I set the currency Decimals to 4 the order calculations are correct:

 

 

 

[Nickz]

Is that the only rule you set?

[Jacek Es]

Yes. This is a fresh installation and I have chosen the already preconfigured UK 20% VAT tax and added the Specific price by discount: -31% from 1000pcs. No additional rules

[Jacek Es]

It appears that the PS calculations may be correct based on the following:

 

Rounding mode: Round on each item

Product base price: £0.30

Discount applied at 1000pc: -31%

Price after discount excl. VAT: £0.207, rounded to £0.21

20% VAT applied to each item: £0.21 * 0.20 = 0.042, rounded to £0.04

Item price, incl. VAT: £0.21 + £0.04 = £0.25

Total for 1000pcs: £0.25 * 1000 = £250

 

In this example VAT is added to each item and then multiplied by quantities? Is there a way of changing this that first is a total calculated excl. VAT and then VAT is added? This would make the calculations more clear and avoiding rounding differences.

 

 

[Nickz]

I'm pretty sure that under the 1000s of modules one offers just that. If not a custom module is often not so expensive.
Just don't ask here. People doing modules sometimes believe you are Bill Gates.