Add tax to a price, strip tax back out of a total, or work out what rate was charged — pick what you're solving for below.
Quick answers to the questions people ask most about sales tax.
Multiply the price by the tax rate (as a decimal) to get the tax amount, then add that to the price. For example, $80 at 7.5% tax is $80 × 0.075 = $6 tax, for a total of $86.
Divide the total by (1 plus the tax rate as a decimal). For example, an $86 total at 7.5% tax means the pre-tax price was $86 ÷ 1.075 = $80.
Subtract the pre-tax price from the total to get the tax charged, divide that by the pre-tax price, then multiply by 100. $6 tax on an $80 item is (6 ÷ 80) × 100 = 7.5%.
Yes. Sales tax rates are set at the state, county, and sometimes city level in the US, so the same item can be taxed differently depending on where it's purchased.