How to use this calculator
Choose add tax or reverse tax. Enter the amount and the applicable percentage. The result shows pre-tax amount, tax and total.
The math behind it
Add: tax = base × rate ÷ 100; total = base + tax Reverse: base = total ÷ (1 + rate ÷ 100); tax = total − base
A worked example
100 before tax at 8.25% becomes 108.25. Reversing 108.25 at the same rate recovers a pre-tax amount of 100.
Assumptions & precision
A single user-entered rate applied to the entire entered taxable amount. No automatic local rates, product exemptions, tax-on-tax, multi-rate baskets or jurisdiction-specific rounding rules. Not tax filing guidance. Currency changes display only; no exchange-rate conversion. Money is rounded only for display using the currency’s fractional digits. Results above 10¹⁵ are rejected.
A common question
Can I subtract the tax percentage from a tax-inclusive total?
No. The rate is based on the pre-tax price. Divide the total by 1 plus the rate to recover that base.