What Reverse Sales Tax Means
Reverse sales tax means starting with the final amount you paid and working backwards to find the original pre-tax price. Instead of adding tax onto a subtotal, you are removing tax from a total.
This comes up in expense reports, bookkeeping, refund reviews, reimbursement requests, and plain old receipt checking. Whenever you know the final charge but need the untaxed amount, this is the calculation you want.
The Formula
Original Price = Total Amount / (1 + Tax Rate / 100)
Tax Amount = Total Amount - Original PriceThe important thing is that you divide the total. You do not subtract the tax percentage from the final amount and call it done.
Worked Example
If the total is $54.12 and the combined sales tax rate is 8.25%, the steps are:
- Convert the rate to a decimal: 8.25 / 100 = 0.0825
- Add 1: 1 + 0.0825 = 1.0825
- Divide the total: $54.12 / 1.0825 = $50.00
- Subtract to find the tax: $54.12 - $50.00 = $4.12
Why Simple Subtraction Fails
Suppose you paid $108.00 total at an 8% rate. If you subtract 8% from $108.00, you get $99.36. That is not the original price. The real pre-tax amount is $100.00 because the tax was calculated on the original subtotal, not on the final total.
Where the Right Rate Matters
In the US, the right rate is usually the combined rate: state plus city, county, and any district add-ons. Using only the state rate can shift the answer enough to matter on larger receipts.
Start with our state and city rate pages if you need a state or local rate, or use the reverse sales tax calculator if you already know the number.