How this works
Sales tax is a percentage-based consumption tax added to the price of taxable goods and services at the point of sale. The math is trivial — multiply the pre-tax amount by the rate to get the tax, add to get the total — but the tricky part in real life is which rate applies, since US sales tax is one of the most fragmented tax systems in the world: 45 states levy a state sales tax, most also have county and city add-ons, and many have special districts for transit, hospitals, or stadiums. A purchase in Chicago, IL faces a combined 10.25% rate from state, county, city, and the regional transit authority. The "sales tax rate" you owe is the sum of all of those layers, and it can change at the city limits.
The tool above does the arithmetic for whatever total rate you enter; figuring out the right rate is on you. Common reference points: California state base is 7.25% (highest US state base; cities can add up to ~3% on top), Tennessee state is 7% but localities push it to ~9.5%; Oregon, Montana, New Hampshire, Delaware and Alaska have no state sales tax (Alaska localities can have their own); New York City's combined is 8.875%; Texas combined typically lands at 8.25%. Most retail e-commerce now collects based on the destination address ("destination sourcing") thanks to the 2018 Wayfair Supreme Court ruling, so the rate you pay online matches what you'd pay in your local store.
A reverse-extract feature handles the common case where you have a receipt with a tax-included total and need to know how much was tax. The formula is pre_tax = total / (1 + rate/100), and tax = total − pre_tax. This comes up constantly for expense reports, restaurant tips (you typically tip on the pre-tax amount), and back-calculating profit margins on tax-inclusive sticker prices common in countries like Japan and the UK. For VAT systems (most of Europe, the UK, Canada GST, Australia GST), the math is identical — the tool works for any consumption tax with a flat percentage rate; the difference is purely terminology and which body collects it.
The formula
pre_tax is the price before sales tax. rate is the combined sales tax percentage at your location (sum of state, county, city, and any special-district rates). total is the amount you actually pay or paid (price with tax included). The tool below switches between the two formulas via the mode toggle so you don't have to remember which one to apply.
Example calculation
- Add 8.25% sales tax to a $120 pre-tax purchase.
- Tax = 120 × 0.0825 = $9.90. Total = 120 + 9.90 = $129.90.
- Reverse: a receipt shows a $54.18 total at 8.25% tax. What was the pre-tax amount?
- Pre-tax = 54.18 / 1.0825 = $50.05. Tax = 54.18 − 50.05 = $4.13. The $4.13 of tax is what to deduct on a business expense report.
Frequently asked questions
How do I find my exact local sales tax rate?
Each US state's Department of Revenue publishes a rate-lookup tool keyed by ZIP code or street address — the address-level lookup is necessary because rates can change at city limits and even within ZIPs. For Avalara, TaxJar, and Stripe Tax users, the tax engine handles this automatically based on shipping/billing address. For one-off lookups, the cleanest free source is the Tax Foundation's annual state-and-local rate report (national overview) plus the state DoR site (precise local rate). Avoid generic "what's the sales tax in X city" web results — they're often outdated or miss special-district add-ons (transit, stadium, fire). For a business collecting tax, you must use accurate per-address rates and remit the right amount to each jurisdiction; for personal calculations (returns, expense reports) the combined rate from the receipt is what you actually paid.
How is sales tax different from VAT?
Both are consumption taxes that end up paid by the final consumer, but the collection mechanism differs. Sales tax is collected once, at the final retail sale to the consumer. VAT is collected at every step of the supply chain — manufacturer adds VAT when selling to wholesaler, wholesaler adds VAT when selling to retailer, retailer adds VAT when selling to consumer — but each business in the chain reclaims the VAT it paid on its inputs, so the net tax paid is the same as a retail-only sales tax. The math the consumer sees is identical: pre-tax price × (1 + rate/100) = total. Differences that matter to consumers: VAT-inclusive sticker prices are the norm in EU/UK/Japan (price you see is what you pay), while US sales tax is added at checkout (sticker doesn't match register total). For businesses, VAT compliance is much more complex: every transaction generates VAT input credits and outputs that must reconcile.
What items are typically exempt from sales tax?
Varies wildly by jurisdiction, but common exemptions in the US include: unprepared groceries (most states), prescription drugs (almost all), some medical devices, and clothing under a price threshold (a few states like NY, MA, NJ). Several states hold annual "tax-free weekends" around back-to-school for clothing, footwear, and supplies. Online sellers must apply the right exemption rules for each destination — most automated tax engines handle this. For business-to-business sales, resale certificates exempt the buyer from collecting tax (because they'll collect when they re-sell). For nonprofits, charitable purchases are often exempt with proper documentation. Always check the local rules — some categories that "feel" like they should be exempt (e.g. period products) only became exempt recently in many states, and others that "feel" taxable (e.g. food at a restaurant) usually are.