About this tool
The Reverse Sales Tax Calculator works backward from a tax-inclusive total. You already know what you paid and the sales tax rate, and you want to split that figure into the original pre-tax price and the tax portion — useful for expense reports, bookkeeping, and separating tax on a receipt that only shows the grand total.
The formula is pre_tax = total ÷ (1 + rate ÷ 100), and tax = total − pre_tax, which is algebraically the same as tax = total × rate ÷ (100 + rate). Both the pre-tax price and the tax are rounded to the nearest cent, and the tax is computed as total minus the rounded pre-tax so the two pieces always add back up to the exact total you entered — any one-cent rounding drift is absorbed into the tax component rather than left as a mismatch.
All calculation happens in your browser, so nothing is sent anywhere. As with a forward sales-tax calculation, the rate can be split into a state rate and a local (county/city) rate; the tool uses their sum as the denominator. The effective-rate readout (tax ÷ pre-tax × 100) should equal the combined rate, confirming the reverse split is consistent.