How to Calculate Sales Tax

Updated October 24, 2026

To add sales tax, multiply the price by 1 plus the tax rate: $49.99 at 8.25% is $49.99 × 1.0825 = $54.11. To take tax out of a total, divide instead: $108.25 ÷ 1.0825 = $100.00. Subtracting 8.25% of the total, a very common mistake, gives the wrong answer.

The three sales tax questions

1. What will this cost with tax?

Convert the rate to a decimal (8.25% is 0.0825), add 1, and multiply.

On coolca.lc's main calculator you can also type it the way you'd say it: $49.99 + 8.25% gives $54.11. See how percentages work.

2. What was the price before tax?

This is the one people get wrong. If a receipt says $108.25 with 8.25% tax included, it's tempting to take 8.25% off: $108.25 − $8.93 = $99.32. But the tax was 8.25% of the price, not of the total, so that undercounts. Divide by 1 plus the rate instead:

You'll need this for expense reports that ask for the pre-tax amount, for checking that a "tax included" price is fair, and for working out tax on a business purchase.

3. What tax rate was I charged?

Divide the total by the price, subtract 1, and turn it into a percentage:

The answer can come out a hair off the real rate, here 8.24% instead of 8.25%, because the total on a receipt is rounded to the cent. On a bigger purchase, the rounding matters less and the rate comes out exact.

How sales tax works in the US

US sales tax isn't one rate. It's usually a state rate plus county, city and sometimes special-district rates, added together into a combined rate for each location. Two stores a few miles apart can charge different rates, and the rate on your receipt is the combined one for where you bought it.

• Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire and Oregon. Alaska lets local governments charge their own, so some purchases there are still taxed.
• What's taxed varies. Many states exempt groceries or tax them at a lower rate, and treatment of clothing, prescriptions and services differs from state to state. A receipt can have taxed and untaxed items side by side.
• Rates change. Cities and counties adjust their rates from time to time. For a current rate, check your state's department of revenue, or work it out from a recent receipt with the formula above.

Prices in US stores are shown before tax, and tax is added at the register. That's why a $9.99 item never costs $9.99.

VAT, GST and tax-included prices

In much of the world, prices are shown with tax already included: value-added tax (VAT) in the UK and Europe, goods and services tax (GST) in places such as Australia and New Zealand. The math is the same, just used the other way around. To find the price before VAT, divide the price by 1 plus the VAT rate: a £120 price with 20% VAT is £100 before VAT, and £20 of it is tax. The Sales Tax Solver works for VAT and GST; the labels say "tax", and the formula doesn't mind what the tax is called.

Using the Sales Tax Solver

coolca.lc's Sales Tax Solver answers all three questions. It has three slots: Price, Tax % and Total. Fill in any two, and the third shows SOLVE.

Adding tax

1. Open Sales Tax.
2. Type the price, such as 49.99, and tap Price.
3. Type the rate, such as 8.25, and tap Tax %.
4. Tap Total, which shows SOLVE.

Removing tax

1. Type the total, such as 108.25, and tap Total.
2. Type the rate and tap Tax %.
3. Tap Price, which shows SOLVE.

Finding the rate

Store the price in Price and the total in Total, then tap Tax %.

Every slot keeps its value, so you can change the rate and see the new total at once, or save your local rate in a Memory preset to recall whenever you need it.

Questions