The formulas
Total = price + tax = price × (1 + rate ÷ 100)
Price before tax = total ÷ (1 + rate ÷ 100)
On an $80 item with an 8.25% tax rate, the tax is $6.60 and the total is $86.60. Going the other way, a receipt total of $86.60 with 8.25% tax included means the original price was $86.60 ÷ 1.0825 = $80.00.
A common mistake when removing tax
You cannot find the pre-tax price by subtracting the tax rate from the total. On a $108 total with 8% tax, taking off 8% gives $99.36, which is wrong. The correct price is $108 ÷ 1.08 = $100, because the tax was calculated on the pre-tax price, not on the total.
Sales tax in the United States
There is no federal sales tax in the U.S. Sales tax is set by states, and many counties and cities add their own on top, so the combined rate depends on the exact location. A handful of states, including Delaware, Montana, New Hampshire and Oregon, have no statewide sales tax, though local taxes can apply elsewhere. Some items, such as certain groceries and clothing, may be taxed at a lower rate or exempt. Look up the current rate for your address before relying on an estimate.
VAT and GST
Many countries use value-added tax (VAT) or goods and services tax (GST) instead. Prices in those places often already include the tax. Choose "Total including tax" and enter the rate to find the price before tax and how much of the total is tax. The same formulas apply.