The basic formula: multiply the price by the tax rate
Sales tax is calculated by taking the item's price and multiplying it by the tax rate for your location. The result is the amount of tax you owe. If an item costs $100 and your sales tax rate is 8%, you multiply $100 by 0.08 to get $8 in tax. Your total cost is $108.
The tax rate varies by state and sometimes by county or city within a state. Some states have no sales tax at all. Others range from 4% to over 10%. You need to know the rate where you are making the purchase, not where you live.
Most of the time, the cashier or checkout system does this math for you. But understanding how it works helps you spot errors and plan your budget before you buy.
Key Takeaways
- Multiply the item price by the tax rate as a decimal (8% becomes 0.08) to find the tax amount.
- Tax rates vary by state, county, and sometimes city, so the same item costs different amounts in different places.
- Some items like groceries or prescription medications are exempt from sales tax in many states.
- When multiple items are taxed at different rates, calculate the tax on each group separately, then add them together.
- Online purchases may or may not be taxed depending on the seller's location and your state's rules.
Converting the tax rate to a decimal
Tax rates are usually shown as percentages. To use them in math, you convert the percentage to a decimal by dividing by 100. A 7% tax rate becomes 0.07. A 10.5% rate becomes 0.105. A 5% rate becomes 0.05.
Once you have the decimal, multiply it by the price. If a shirt costs $50 and the tax rate is 7%, you calculate: $50 × 0.07 = $3.50 in tax. The total you pay is $50 + $3.50 = $53.50.
This works the same way whether you are buying one item or many. Calculate the tax on each item (or group of items at the same rate), then add all the taxes together to get your total tax amount.
When different items have different tax rates
Some states tax groceries at a lower rate than clothing, or don't tax groceries at all. Prescription medications are often tax-exempt while over-the-counter drugs are taxed. When you buy a mix of items with different rates, you calculate the tax on each group separately.
For example: you buy groceries for $40 (taxed at 0%), a shirt for $30 (taxed at 8%), and a book for $15 (taxed at 0%). The tax is: ($40 × 0) + ($30 × 0.08) + ($15 × 0) = $0 + $2.40 + $0 = $2.40. Your total is $40 + $30 + $15 + $2.40 = $87.40.
The cashier's register knows which items are taxable in your state and applies the right rate to each one. If you are calculating by hand, check your receipt to see which items were taxed and at what rate.
Finding your local sales tax rate
Your state's sales tax rate is public information. You can find it by searching "[your state] sales tax rate" online, or by visiting your state's Department of Revenue website. Many states list both the state rate and any additional county or city rates that apply to your area.
Some locations have a single combined rate. Others require you to add the state rate plus the local rate. For example, if your state charges 6% and your county adds 2%, the total rate is 8%. A $100 purchase would be taxed at 8%, not 6%.
If you are shopping in a different state or county, the rate may be different from your home location. Gas stations, restaurants, and stores often post the local rate, or you can ask the cashier.
Sales tax on online and mail orders
Whether you pay sales tax on an online purchase depends on where the seller is located and your state's rules. If the seller has a physical location or warehouse in your state, they usually must collect sales tax from you. If they are located out of state and have no presence in your state, they may not collect tax at the checkout.
Some states require you to report and pay tax on out-of-state purchases yourself on your tax return, though this is rarely enforced for individual shoppers. Check your state's Department of Revenue website if you want to know the exact rule for your location.
Major online retailers like Amazon now collect sales tax in most states, even when they ship from out of state. Smaller sellers and marketplaces vary. The tax (or lack of tax) should show on your receipt or order confirmation.
Common items that are often tax-exempt
Many states do not tax certain items. Groceries and food for home consumption are exempt in most states, though prepared food and restaurant meals are usually taxed. Prescription medications are exempt in nearly all states. Clothing is tax-exempt in some states but taxed in others.
Medical equipment, educational materials, and items for people with disabilities may also be exempt depending on your state. Some states exempt items bought for resale by a business. The rules vary widely, so what is tax-exempt in one state may be taxed in another.
If you are unsure whether an item is taxable, check your receipt after purchase or contact your state's Department of Revenue. The cashier may also know, especially for common categories like groceries or medications.
Frequently Asked Questions
How do I calculate tax if the price tag doesn't show it?
Multiply the price by the tax rate as a decimal. If the tag says $25 and your tax rate is 9%, multiply $25 by 0.09 to get $2.25 in tax. Add that to the price: $25 + $2.25 = $27.25 total. You can also search your state's sales tax rate online if you don't know it.
Why is my receipt total different from what I calculated?
The most common reason is that some items on your receipt are tax-exempt while others are taxed. Groceries, medications, and clothing may be taxed at different rates or not taxed at all. Check which items show a tax amount on your receipt and recalculate using only those items.
Do I pay sales tax on used items?
Used items sold by individuals are usually not taxed. Used items sold by a business or reseller are often taxed at the same rate as new items, though some states have lower rates for used goods. Check your receipt or ask the seller if you are unsure.
What if I buy something in one state and use it in another?
You pay sales tax based on where you make the purchase, not where you use the item. If you buy something in a state with no sales tax and take it home to a state with sales tax, you do not owe tax. Some states ask you to report and pay tax on out-of-state purchases, but this is rarely enforced.