The sales tax formula
Sales tax is a percentage added to the price of goods and services at the point of sale. Adding it is straightforward:
Going the other way — finding the original price hidden inside a tax-inclusive total — is the reverse calculation:
The rate must be written as a decimal in the math: 7% becomes 0.07. The calculator above accepts a percentage and converts it for you.
Worked example
Adding tax. A $50 item in a place with a 7% combined rate:
Reversing tax. You paid $53.50 and want to know the pre-tax price at 7%:
US sales tax varies by location
There is no federal sales tax in the United States. Each state sets its own base rate, and counties and cities frequently add local taxes on top, so the combined rate at the register depends on exactly where the sale happens. A handful of states — including Oregon, Delaware, Montana and New Hampshire — have no statewide sales tax at all. Always confirm the combined rate for the specific jurisdiction.