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Sales Tax Calculator

Add tax to a price, or reverse-engineer the pre-tax amount from a tax-inclusive total.

Sales-tax math is grade-school arithmetic, but the reverse case trips people up: given a $108 receipt and an 8% rate, the pre-tax amount is 108 ÷ 1.08 = 100, not 108 − 0.08 × 108 = 99.36. The widget below handles both directions accurately, with a switch at the top so it’s clear which one you’re running.

Pre-tax
$100.00
Tax
$8.00
Total
$108.00

How to use

  1. Pick the direction

    "Add tax" goes from pre-tax to total. "Find pre-tax" goes from a tax-inclusive total back to the pre-tax amount.

  2. Enter amount and rate

    Both fields accept any positive decimal — 6.625% for New Jersey, 8.875% for New York City, etc.

  3. Read all three numbers

    The widget always shows pre-tax, tax, and total. The highlighted box is the one you were solving for.

Frequently asked questions

Why isn't reversing tax just subtracting the percentage?
Because the tax was applied to a different base. The pre-tax amount × (1 + rate) = total. Solving for pre-tax gives pre-tax = total ÷ (1 + rate). Subtracting the percentage uses the larger total as the base and consistently under-estimates the pre-tax figure.
Does this know my local sales-tax rate?
No — there are over 13,000 sales-tax jurisdictions in the US alone. Look up your rate once and the calculator handles the math from there.
Can I model compound taxes (e.g., GST + PST in Canada)?
Yes — calculate it in two steps. Add the first tax, take the result, then add the second tax on the new total or on the original pre-tax base, depending on which model your province uses.
Does the calculator store my data?
No. Every computation runs in your browser.

About

Where this calculator helps most

Receipts where tax was bundled into the line items (rare in the US, common in Europe / Australia / Japan VAT regimes), expense-report exports that need pre-tax columns, or back-of-the-envelope estimates when you only have a tax-inclusive total.

Round-trip accuracy

Adding tax and then reversing it round-trips to within IEEE 754 double precision — typically 15-16 significant digits. The calculator doesn't introduce additional rounding.