About the Sales Tax Calculator
Sales tax, VAT and GST are all consumption taxes, and the single most common mistake is working backwards. People subtract the rate from the tax-inclusive total, which always understates the tax and overstates the pre-tax price, because the tax was charged on the smaller pre-tax amount rather than on the total.
This calculator does both directions properly: forward to add tax to a net price, and reverse to divide it back out of a gross total. Rates are free-form, so it works for a US state sales tax, UK VAT, Australian GST, or any other percentage.