Reverse Sales Tax Calculator
Enter a total that already includes tax and the tax rate to find the original price before tax and exactly how much tax was added.
When a price already includes tax, you can't just subtract the tax percentage — the tax was added to the smaller pre-tax price, not the total. This calculator does the correct reverse calculation for you.
How to back sales tax out of a total
Divide the tax-inclusive total by one plus the tax rate. The result is the pre-tax price; the difference is the tax.
Pre-tax price = Total ÷ (1 + Tax rate ÷ 100)
Tax amount = Total − Pre-tax price
Tax amount = Total − Pre-tax price
| Term | Meaning |
|---|---|
| Total amount | The final price you paid, tax included |
| Tax rate | The sales tax, VAT or GST percentage applied |
| Pre-tax price | The original price before tax was added |
Worked example
A total of 107.00 at a 7% tax rate:
| Pre-tax = 107 ÷ 1.07 | 100.00 |
| Tax = 107 − 100 | 7.00 |
Notice that 7% of 100 is 7 — but 7% of the 107 total would be 7.49, which is why the reverse calculation matters.
Frequently asked questions
How do you calculate reverse sales tax?
Divide the total (which includes tax) by 1 plus the tax rate as a decimal. For 8% tax, divide by 1.08. The answer is the pre-tax price, and the rest is the tax.
Can I use this for VAT or GST?
Yes. The math is identical — enter your VAT or GST rate (for example 20% UK VAT, 10% Australian GST, or 5% Canadian GST) as the tax rate.
Why can't I just subtract the tax percentage?
Because the tax was calculated on the smaller pre-tax price, not the total. Subtracting the percentage from the total overstates the tax.
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For general information only. Rounding on receipts can cause a small difference from a retailer's exact figures. Not financial or tax advice.