Reckonary / Finance / Reverse sales tax
Price before tax
Sometimes all you have is the final total on a receipt and you need to know the listed price before tax — for an expense report, a refund, or bookkeeping. A reverse sales tax calculator does exactly that: it takes the tax-included total and your local rate and pulls out both the pre-tax price and the tax that was added.
The tax was charged on the pre-tax price, not on the total, so you can't just multiply the total by the rate. Instead you divide it back out. Pre-tax price equals the total divided by (1 + rate/100), and the tax is whatever's left when you subtract the pre-tax price from the total. The ledger bar under the result shows how much of what you paid was tax.
Say a receipt shows $107.00 and your combined sales tax rate is 7%. Dividing 107 by 1.07 gives a pre-tax price of $100.00, which means $7.00 of the total was tax. Set the rate to 0% and the pre-tax price simply equals the total, since nothing was added.
What does a reverse sales tax calculator do?
It starts from the total you actually paid, with tax already included, and works backward to show the listed pre-tax price and how much of that total was tax.
What's the formula?
Pre-tax price equals the total divided by (1 + rate/100). The tax is the total minus that pre-tax price. For a $107 total at 7%, the pre-tax price is $100.00 and the tax is $7.00.
Why not just multiply the total by the tax rate?
Because the tax was charged on the pre-tax price, not on the total. Multiplying the total by the rate overstates the tax, so you have to divide the total out first.
Where do I find my sales tax rate?
Rates depend on your state, county, and sometimes city, so they vary widely. Check your receipt or your state revenue department's site for the combined rate that applies at the point of sale.
Last reviewed June 2026. Sales tax rates vary by location — check your local rate.