How sales tax is added in this tool

The sales tax calculator has two directions and one rate field. You type the percent. The site does not store a table of the 50 states, and it does not fill in California, New York, or any other jurisdiction.

When the amount you enter is before tax, the calculator uses amount with tax = pre-tax × (1 + tax percent ÷ 100). One hundred dollars and 8 percent produce $108.00. The tax amount is the difference after both figures are rounded to the nearest cent with half-up rounding.

When the amount you enter already includes tax, the calculator uses pre-tax = amount with tax ÷ (1 + tax percent ÷ 100). One hundred eight dollars and 8 percent return $100.00. On some other rates, rounding to the cent can leave a one-cent difference on the way back.

The pre-tax amount is the number before sales tax. The with-tax amount is the number after sales tax. Those labels stay on the readout, so the direction is visible. The calculator does not add tax to a tip unless you are on the tip page and you chose that rule.

Rates change by city and by year. The honest input is the percent on the receipt or the percent you were told to use. This guide does not estimate a state rate, and it does not compute a paycheck withholding.