US sales tax has no single number — the rate charged at checkout is a stack of state, county, city, and sometimes special-district taxes that changes from one side of a street to the other. This calculator does the one part that's actually math: add tax to a price you're about to charge, or back the tax out of a total you already have, once you know the combined rate that applies. It won't tell you what that rate is — that depends on where the sale happens and what's being sold — but it will get the arithmetic right every time you use it.
How it works
In add mode, you enter a pre-tax price and a rate. The tax is the price times the rate, and the total is the price plus that tax — the calculation most people picture when they think "sales tax."
Remove mode solves the opposite problem, and it's the one people get wrong by hand. If a total already includes tax — a receipt, a tax-inclusive listed price, a lump sum you collected — you can't just subtract the rate from the total, because the rate was applied to the pre-tax price, not to the total itself. Instead, the total equals the pre-tax price times (1 + rate), so dividing the total by (1 + rate) recovers the original pre-tax price. The tax is whatever's left after subtracting that pre-tax price from the total.
Both modes round each dollar figure to the cent from the unrounded math, so the tax and the total or pre-tax amount always add up correctly against each other, no matter which direction you're solving.
Worked example
A $100 pre-tax price with an 8.25% combined rate, in add mode:
- Sales tax: $100 × 8.25% = $8.25
- Total: $100 + $8.25 = $108.25
Now flip it: someone hands you a $107.99 total that already includes a 7.25% rate, and you need the pre-tax amount for your books. Divide, don't subtract:
- Pre-tax amount: $107.99 ÷ 1.0725 = $100.69
- Sales tax: $107.99 − $100.69 = $7.30
Notice the tax isn't 7.25% of $107.99 (that would overstate it at $7.83) — it's 7.25% of the pre-tax $100.69, which is exactly $7.30 within rounding. That gap is the whole reason remove mode exists as its own calculation instead of a quick mental shortcut.
How to interpret your result
The number you actually want depends on why you're calculating. Quoting a client or pricing a product: use add mode and the total is what you charge. Reconciling a receipt, extracting tax paid from a lump-sum reimbursement, or figuring out how much of a marketplace payout was tax you collected on someone's behalf: use remove mode and the pre-tax amount is your real revenue figure, not the total.
Whatever rate you enter is doing all the work, and getting it wrong by even a fraction of a point compounds across every transaction you run through it. The safest source is the rate your point-of-sale system or payment processor already calculates for a specific address, since combined rates are set at the jurisdiction level and can differ between two addresses a few blocks apart — same city, different total. Treat the 8.25% default here as a placeholder, not a rate for your business.
Methodology & sources
Add mode: salesTax = round2(amount × rate / 100), total = round2(amount + salesTax). Remove mode: preTaxAmount = round2(amount / (1 + rate / 100)), salesTax = round2(amount − preTaxAmount), with total equal to the tax-inclusive amount you entered. This is standard percentage-of-base arithmetic, not a tax rule — it doesn't encode exemptions, product-category carve-outs, or nexus thresholds, and it doesn't know which jurisdiction's rate should apply to a given sale.
For a sense of how much combined rates vary across the US, the Tax Foundation's State and Local Sales Tax Rates, 2026 report puts the population-weighted average combined state-and-local rate at 7.53%, with five states (Alaska, Delaware, Montana, New Hampshire, Oregon) levying no statewide sales tax at all and Louisiana topping the list at just over 10%. That spread is exactly why this tool asks you to supply your own rate instead of guessing one for you — look yours up for the specific sale before you rely on the result.