The basic formula for sales tax

Sales tax is a percentage of the purchase price that you owe to your state or local government at the time of sale. To calculate it, multiply the price of the item by the tax rate, then add that amount to the original price.

The formula is: Purchase Price × Tax Rate = Sales Tax Amount. Then add the sales tax to the purchase price to get your total cost.

For example, if you buy an item for $100 and the sales tax rate is 8%, you multiply $100 by 0.08 to get $8 in sales tax. Your total cost is $100 + $8 = $108.

Key Takeaways

  • Sales tax rates vary by state and sometimes by county or city, so the same item costs different amounts in different places.
  • You calculate sales tax by multiplying the item price by the tax rate as a decimal (8% becomes 0.08).
  • Some items are exempt from sales tax in most states, including groceries, prescription medications, and medical equipment.
  • Online purchases are subject to sales tax in most states, though the rate depends on where the item ships to, not where the seller is located.
  • Sales tax is collected at the point of sale — the cashier or checkout system calculates and adds it automatically in most cases.

Why sales tax rates differ by location

Sales tax is not uniform across the country. State rates range from 0% (in states like Delaware, Montana, New Hampshire, and Oregon) to over 7% in some states. Within states that have sales tax, individual counties and cities often add their own local tax on top of the state rate.

For example, Colorado's state sales tax is 2.9%, but Denver adds 3.62%, making the total rate 6.52% in that city. The same item bought in a different Colorado county might have a different total rate. When you see a sales tax rate listed, it usually reflects the combined state and local rate for that specific location.

How to find the sales tax rate for your area

Your state's Department of Revenue website lists the current state rate and explains which items are taxed. To find the exact rate in your city or county, search "[your state] sales tax rate" or "[your city] sales tax rate" online. Most state revenue departments have a tax rate lookup tool where you enter your zip code and see the combined rate.

If you are buying online, the seller's checkout page should show you the tax rate applied to your order. That rate is based on the shipping address you provide, not on where the seller operates. If the rate shown seems wrong, double-check your zip code in the checkout form.

Items that are usually exempt from sales tax

Most states do not charge sales tax on certain categories of goods. The most common exemptions are groceries (unprepared food), prescription medications, and medical devices prescribed by a doctor. Some states also exempt clothing, school supplies, or energy sources like electricity and natural gas.

Exemptions vary significantly by state. For instance, some states tax groceries while others do not. Prepared food — meals at restaurants or hot food from a deli — is almost always taxed, even in states that exempt unprepared groceries. If you are unsure whether an item is taxed, check your state's Department of Revenue website or ask the cashier before you pay.

Calculating tax on multiple items

When you buy more than one item, you can calculate the total sales tax in two ways. The first way is to add up all the prices, then multiply the total by the tax rate. The second way is to calculate the tax on each item separately, then add all the tax amounts together. Both methods give the same result.

For example, if you buy three items for $20, $30, and $50 (total $100), and the tax rate is 7%, you multiply $100 by 0.07 to get $7 in tax. Your total cost is $107. In a real store, the register does this automatically and shows you the subtotal, tax amount, and total on your receipt.

Sales tax on online and mail orders

Online retailers must collect sales tax on orders shipped to states where they have a physical presence or meet certain sales thresholds. The tax rate applied is based on the shipping address you provide, not the seller's location. If you order something online and it ships to your home, you pay the sales tax rate for your zip code.

Some online sellers may not collect sales tax at checkout, but that does not mean the purchase is tax-free. Depending on your state's rules, you may owe "use tax" on the item — a tax you pay directly to your state instead. Most people do not pay use tax voluntarily, but some states pursue it for large purchases. Check your state's Department of Revenue website if you want to understand your state's use tax rules.

Working backward from a total price

If you know the final total and want to find out how much tax was included, you can work backward. Divide the total by (1 + the tax rate as a decimal). For example, if your total is $107.50 and the tax rate is 7%, divide $107.50 by 1.07 to get $100.47 as the pre-tax price. The tax amount is $107.50 minus $100.47, which is $7.03.

This calculation is useful if you are reviewing a receipt and want to verify the math, or if you are tracking business expenses and need to separate the tax from the purchase price for accounting purposes.

Frequently Asked Questions

Do I have to pay sales tax on everything I buy?

No. Most states exempt groceries, prescription medications, and medical equipment. Some states also exempt clothing or school supplies. Prepared food, alcohol, and tobacco are almost always taxed. Check your state's Department of Revenue website to see the full list of exemptions where you live.

Why is the total on my receipt different from what I calculated?

The most common reason is rounding. When tax is calculated on each item separately (rather than on the subtotal), small rounding differences can add up. Also, some items may be exempt from tax while others are not, so the tax rate does not apply to the entire purchase. Review your receipt to see which items were taxed.

Do I owe sales tax on items I buy out of state?

You owe sales tax based on where the item is shipped to, not where you buy it. If you order something online and have it shipped to your home, you pay the tax rate for your state and zip code. If you travel to another state and buy something in a store there, you pay that state's tax rate at the register.

What is the difference between sales tax and use tax?

Sales tax is collected by the seller at the point of sale. Use tax is a tax you owe to your state on items you buy from out-of-state sellers who did not collect sales tax. Most people do not pay use tax voluntarily, but your state may pursue it for large purchases. Ask your state's Department of Revenue about use tax rules in your area.

Can I get a refund of sales tax I already paid?

In most cases, no. Sales tax is final once you pay it. However, if you return an item and get a refund, the store will refund the tax as well. Some states offer sales tax refunds for specific situations, such as purchases made for business use or by nonprofit organizations, but these are exceptions. Check with your state's Department of Revenue if you think you may be may have access to to a refund.