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Sales Tax Calculator

Add sales tax to a price, or work backwards from a total to find what the item cost before tax.

Enter an amount and your sales tax rate.

Which way?

Your full combined rate — state plus any county, city and district tax. A recent receipt is the quickest source.

Exact calculation. Given your inputs, this is the answer — no estimation involved.

How this calculator works

Adding tax is straightforward: multiply the price by the rate and add it on. A $49.99 item at 8.25% carries $4.12 of tax, for a total of $54.11.

Working backwards is where people go wrong. To find the pre-tax price from a total, you divide by 1 plus the rate — you do not subtract the percentage. Taking 8.25% off a $100 total gives $91.75, but the real pre-tax price is $92.38. The tax was charged on the smaller number, so subtracting it from the larger one takes off too much.

That gap widens with the rate. At 2% it is about four cents on $100; at 11% it is over a dollar. If you are separating tax on an expense claim or a set of receipts, the error compounds across every line.

Nothing here is rounded. Real registers round tax per line or per subtotal depending on state rule, so a receipt can differ from this by a cent or two.

The formula

Exactly what happens to your numbers, step by step.

  1. Adding tax

    tax   = price × rate
total = price + tax

  2. Removing tax

    price = total ÷ (1 + rate)
tax   = total − price

    Divide, never subtract. Subtracting the percentage from the total is the common mistake.

A worked example

A receipt totals $100.00 and the sales tax rate is 8.25%. What did the item cost?

What you enter

Total including tax
$100.00
Sales tax rate
8.25%

The working

The wrong way
$100 × (1 − 0.0825) = $91.75
The right way
$100 ÷ 1.0825 = $92.38
So the tax was
$100 − $92.38 = $7.62
Check it
$92.38 × 1.0825 = $100.00 ✓

$92.38 before tax, $7.62 of tax

The wrong method is off by 63 cents on a single $100 receipt. Note that the tax is $7.62 rather than $8.25 — because 8.25% was charged on $92.38, not on the $100 total.

Assumptions

Every result here rests on these. Change your inputs and the result changes with them.

  • A single tax rate applies to the whole amount.
  • The rate you enter is your full combined rate — state plus any county, city and district taxes.
  • Nothing is rounded, so the figures may differ by a cent or two from a printed receipt.

What this cannot tell you

  • It cannot look up your rate. A US sales tax rate is a state rate with county, city and special-district rates stacked on top, across more than eleven thousand taxing jurisdictions — two addresses on opposite sides of one street can pay different rates, and rates change on quarterly cycles. A dropdown of state rates would be correct about a component and wrong about the answer, which is worse than no number at all.
  • It does not know what is taxable. Most states exempt groceries and prescription drugs, some exempt clothing below a threshold, and rules differ for prepared food, digital goods and services.
  • Mixed baskets are not handled. If some items are taxable and some are exempt, run them separately.
  • Sales tax holidays, tribal jurisdictions, and special rates on vehicles, alcohol or lodging are not modelled.
  • This is US sales tax arithmetic. VAT and GST work the same way mathematically, but their registration, reclaim and invoicing rules do not.

Questions people ask

How do I calculate sales tax backwards from a total?

Divide the total by 1 plus the rate as a decimal. For 8.25%, divide by 1.0825. Do not subtract 8.25% from the total — that removes too much, because the tax was charged on the pre-tax price rather than on the total.

Why is subtracting the percentage wrong?

Because a percentage is always of something, and here it was of the smaller number. $92.38 plus 8.25% is $100. But $100 minus 8.25% is $91.75, since 8.25% of $100 is larger than 8.25% of $92.38. The difference is the tax on the tax.

What sales tax rate should I enter?

Your full combined rate. The quickest source is a recent receipt from the same area, which prints the rate or lets you derive it. Failing that, most state revenue departments publish an address-based rate lookup — address-based precisely because the rate can change street by street.

Which states have no sales tax?

Alaska, Delaware, Montana, New Hampshire and Oregon have no statewide sales tax. Alaska is the catch: it has no state rate but allows local ones, so many Alaskan towns do charge sales tax. The other four generally do not.

Does this work for VAT or GST?

The arithmetic is identical — adding and removing a percentage works the same way for VAT, GST or any inclusive tax. What differs is everything around it: registration thresholds, reclaiming input tax, and invoice requirements. Use it for the maths, not for compliance.

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Sources and review

This calculator uses standard arithmetic with no external rules or published rates, so there is nothing to cite beyond the formulas shown above.

Methodology version 1.0.0 · Last reviewed