Sales tax
Tax = amount × rate% · Total = amount + tax
US sales tax is added at checkout rather than shown on the shelf, and combined state + local rates range from 0% to about 10%. To work backwards from a tax-inclusive total: amount = total ÷ (1 + rate).
Adding and removing sales tax
To add tax, multiply the price by the rate and add it on: total = price × (1 + rate ÷ 100). To work backwards from a tax-inclusive total, divide by the same factor. Switch modes above to do either.
Sales tax rates differ by location — enter the combined rate that applies to you.