How sales tax works and how to calculate it

Sales tax is a percentage added to the price of goods (and some services) at the moment of a retail sale. In the United States the shelf price usually excludes it, the shop adds it at the till, and the rate you pay is a combination of state and local rates tied to where the sale happens. Working it out is simple multiplication, and working it backwards from a receipt is simple division. The sales tax calculator does both, and this guide explains the mechanics so you can check any receipt yourself.

What sales tax is

A sales tax is a consumption tax charged once, on the final sale to the customer. The seller collects it from you and passes it to the state, so it never shows up as a bill in your own name. That single collection point is the key difference from value-added tax, which is charged at every step of a supply chain. In the US there is no federal sales tax; it is set by states, and most states also let counties, cities and special districts add their own rates. Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire and Oregon, although some Alaskan towns charge a local one.

Why the rate depends on where you are

The rate on a receipt is usually a stack: a state rate plus one or more local rates. A purchase in a city with a 6% state rate and 2.25% of county and city rates is taxed at 8.25% combined. Two shops a few miles apart can therefore charge different amounts on the same item, and online orders are generally taxed at the rate for the delivery address. Because local rates change often and depend on exact boundaries, the only reliable source for a specific address is the state revenue department, not a national average. I built the calculator with separate state and local fields for exactly that reason: you type in the rates that apply to you, and it adds them.

Adding tax to a price

To add sales tax, multiply the pre-tax price by the rate as a decimal, then add the result:

• Tax = price × rate. At 8.25%, a $100 item carries $100 × 0.0825 = $8.25 of tax.
• Total = price × (1 + rate) = $100 × 1.0825 = $108.25.

Prices with cents work the same way: a $49.99 item at 7.5% has $3.749 of tax, which rounds to $3.75, for a total of $53.74. Shops round to the cent, and states set rules on whether tax is rounded per item or on the whole invoice, so a long receipt can differ from your own sum by a cent or two. That is normal. If you are also working out a sale price, apply the discount first and the tax second; the discount calculator handles that step, and How to calculate percentages covers the percentage arithmetic.

Taking tax out of a total

Going backwards is where most mistakes happen. If a receipt says $108.25 including 8.25% tax, the pre-tax price is not $108.25 minus 8.25%, which gives $99.32. The tax was calculated on the smaller, pre-tax number, so you have to divide: $108.25 ÷ 1.0825 = $100.00. The tax is the difference, $8.25. The calculator's remove-tax mode does this division, and its find-the-rate mode works the other way: give it a price before tax of $80 and a total of $86.40 and it reports 8%, because 86.40 ÷ 80 = 1.08.

Exemptions, holidays and use tax

What is taxed varies as much as the rate. Many states exempt or reduce tax on groceries, prescription medicine or clothing, and some run sales tax holidays, often before the school year, when selected items are tax-free for a few days. Services are taxed in some states and not in others. There is also use tax: if you buy something taxable without paying sales tax, for example from a seller that did not collect it, many states expect you to pay the equivalent use tax yourself. Since a 2018 Supreme Court decision (South Dakota v. Wayfair), states can require large online sellers to collect tax even without a physical presence, so this gap is much smaller than it used to be. On a federal return, people who itemise can choose to deduct state and local sales tax instead of state income tax, subject to the overall cap on state and local tax deductions; the IRS explains the details.

Sales tax vs VAT

Most of the world uses value-added tax (VAT) or a goods and services tax (GST) instead. VAT is charged at each stage of production, with businesses reclaiming the VAT they paid on inputs, so in the end the tax falls on the consumer, much like a sales tax. The visible difference is at the till: in the UK and EU, displayed consumer prices must include VAT, so the shelf price is the price you pay. For those prices use the VAT calculator, and see How VAT actually works for how the chain of reclaims works. The arithmetic for adding and removing tax is identical in both systems; only the rates and the rules about what is shown differ.