To calculate sales tax, multiply the item’s pre-tax price by the combined tax rate for the location of the sale, expressed as a decimal. A $200 purchase at an 8.25% rate produces $16.50 in tax and a $216.50 total. That’s the whole formula. The work that surrounds it is finding the right rate, deciding which items on your receipt the rate applies to, and knowing how to run the math backward when you only have the final total.
The Formula, Step by Step
Convert the rate from a percentage to a decimal by moving the decimal point two places left. 7.5% becomes 0.075. 6% becomes 0.06. 8.25% becomes 0.0825. Then multiply.
For a $150 purchase at 7.5%:
- Convert the rate: 7.5% becomes 0.075.
- Multiply the price by the decimal: $150 × 0.075 = $11.25 in tax.
- Add the tax to the price: $150 + $11.25 = $161.25 total.
If you only want the final total, multiply the price by 1 plus the rate in one step: $150 × 1.075 = $161.25. Same answer. Registers and checkout systems do this automatically, but running it by hand is useful for budgeting before a purchase or checking a receipt afterward.
Finding the Rate to Plug In
Sales tax rates stack. Most locations combine a state rate with add-ons from the county, city, and sometimes special districts like transit authorities or stadium bonds. A shopper in one zip code might pay 6% while someone a few miles away pays 9.5% because they’re inside a city that layers on its own tax. The number you need is the combined rate, not the state rate alone. Combined rates across the country run from zero in the states that don’t charge sales tax up to over 11% in parts of Louisiana, Arkansas, and Oklahoma.
Every state revenue department publishes a rate-lookup tool on its website, usually searchable by address or zip code. Those tools return the full combined rate for that exact spot, local add-ons included. If you’re a business collecting tax, use the rate for the delivery destination rather than your own address, because sales tax is generally owed where the buyer receives the goods.
Five states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire, and Oregon. Alaska is the odd one out because it lets local governments impose their own sales tax even though the state doesn’t, so some Alaskan cities do collect it. In the other four, sales tax simply isn’t part of the transaction.
Working Backward From a Total That Already Includes Tax
This is where people go wrong. If you have a receipt total that includes tax and you want to know the pre-tax price, the instinct is to multiply the total by the tax rate and subtract. That gives the wrong answer every time. The tax was originally calculated on the lower, pre-tax number, so applying the rate to the higher, tax-inclusive total overstates it.
The correct move is to divide the total by 1 plus the tax rate as a decimal. For a $108 receipt in an 8% area, divide $108 by 1.08. The pre-tax price was exactly $100 and the tax was $8. If you had multiplied $108 by 0.08 and subtracted, you would have landed at $99.36, close enough to look right and far enough off to cause trouble in expense reports or bookkeeping.
This reverse calculation is what businesses use to separate tax from gross receipts, what auditors use to verify reported figures, and what anyone splitting a restaurant bill needs when the receipt shows only the total.
Rounding When the Tax Lands Between Cents
Tax math often produces fractions of a cent. A $12.99 item at 8.75% comes to $1.136625 in tax. The standard rule used by most states rounds half a cent or more up to the next cent and drops anything below half a cent, so $1.136625 rounds to $1.14.
A separate wrinkle appeared in 2025 when the federal government stopped manufacturing pennies. Several states have passed or proposed laws on rounding cash transactions to the nearest nickel, but that rounding applies only after the full sales tax has already been calculated on the original price. The tax itself is still computed the same way regardless of how the final cash payment gets rounded.
Adjust for Items That Aren’t Taxed
Not everything on a receipt is taxable, and exemptions change the subtotal you multiply. Apply the tax rate only to the taxable items, then add the exempt items at face value.
Common Exemptions
The widest exemptions cover groceries and prescription medications. Most states exempt unprepared food bought at a grocery store, though prepared food and restaurant meals are almost always taxable. Prescription drugs are exempt in virtually every state. A smaller number of states also exempt clothing and footwear below a certain price. Specifics vary enough that checking your state’s revenue department website before assuming an exemption is worth the two minutes.
Businesses that buy goods purely for resale can avoid paying sales tax on the purchase by giving the supplier a resale certificate. The tax gets collected later from the end consumer instead.
Shipping and Delivery
Whether shipping is taxed depends on the state. In some states, delivery charges on taxable goods are themselves taxable and treated as part of the sale. In others, separately stated shipping charges are exempt even when the product is taxable. A few states split the difference based on whether shipping is a separate line item or bundled into the product price. Before calculating tax on an online order, check whether your state includes delivery fees in the taxable amount, because that changes the number you multiply.
Digital Products
Downloaded software, e-books, streaming subscriptions, and other digital goods sit in a shifting category. A majority of states with sales tax now tax at least some digital products, but what qualifies varies widely. Some states tax downloaded music but not streaming access. Others treat digital and physical goods identically. If you sell digital products across state lines, research each state’s specific rules.
When the Seller Didn’t Charge Tax
If you buy something taxable and the seller doesn’t charge sales tax, which happens with some out-of-state online purchases from smaller retailers, you technically owe an equivalent amount called use tax directly to your state. The rate is the same as your local sales tax rate, and the calculation is identical: price times rate. Many states have added a use tax line to the annual state income tax return to make reporting easier. If you paid sales tax to another state on the same purchase, you generally get a credit for that amount against your home state’s use tax, so you’re only paying the difference if your state’s rate is higher.
For businesses, use tax matters more. Equipment, supplies, and materials bought from out-of-state vendors that didn’t charge tax need to be tracked and self-reported, typically on the same return used for sales tax.