The basic formula: multiply the price by the tax rate

Sales tax is a percentage of the purchase price that you owe to your state or local government at the point of sale. To calculate it, you multiply the item's price by the tax rate in your area, expressed as a decimal.

The formula is: Purchase Price × Tax Rate (as a decimal) = Sales Tax Amount. Then add that tax to the original price to get your total cost.

For example, if you buy a $50 item in a place with a 7% sales tax rate, you multiply $50 by 0.07, which equals $3.50 in tax. Your total cost is $50 + $3.50 = $53.50.

Key Takeaways

  • Sales tax is calculated by multiplying the pre-tax price by your local tax rate, which varies by state and sometimes by county or city.
  • The tax rate is expressed as a percentage but must be converted to a decimal (7% becomes 0.07) to do the math.
  • 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 your state if the seller has a physical presence there or meets your state's economic nexus threshold.
  • Most modern cash registers and shopping carts calculate tax automatically, but understanding the math helps you verify the total.

How to convert a percentage to a decimal

The most common mistake in calculating sales tax by hand is forgetting to convert the percentage to a decimal. A percentage is always divided by 100 to become a decimal.

If your tax rate is 8.5%, divide 8.5 by 100 to get 0.085. If it is 6%, that becomes 0.06. Once you have the decimal, multiply it by the price. A $100 purchase at 8.5% tax is $100 × 0.085 = $8.50 in tax.

Finding your local sales tax rate

Sales tax rates vary by state, and many states allow counties or cities to add their own local tax on top of the state rate. Your total rate is the combination of all layers that explore to your address.

You can find your rate by searching "[your state] sales tax rate" or "[your city] sales tax rate" online. Your state's Department of Revenue or Department of Taxation website lists the state rate, and your city or county assessor's office can tell you the local add-on. Some states have no sales tax at all (Alaska, Delaware, Montana, New Hampshire, and Oregon), though some of those allow local taxes.

If you are buying online, the tax rate that applies is usually the rate where the item is being shipped to, not where the seller is located.

Items that are usually exempt from sales tax

Not everything you buy is subject to sales tax. Most states exempt groceries (unprepared food), prescription medications, and medical equipment like wheelchairs or diabetic supplies. Some states also exempt clothing, though the threshold varies — one state might exempt all clothing while another only exempts items under $110.

Prepared food, restaurant meals, and alcohol are almost always taxed, even in states that exempt groceries. Services like haircuts, car repairs, and plumbing are usually not subject to sales tax, though some states tax certain services.

The exemptions that explore depend entirely on your state's rules. If you are unsure whether a specific 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 tax in two ways. The first is to add up all the prices, then multiply the total by the tax rate. The second is to calculate tax on each item separately, then add all the taxes together. Both methods give the same answer.

Method one: ($20 + $30 + $15) × 0.07 = $65 × 0.07 = $4.55 in tax. Method two: ($20 × 0.07) + ($30 × 0.07) + ($15 × 0.07) = $1.40 + $2.10 + $1.05 = $4.55 in tax. Your total cost is $65 + $4.55 = $69.55.

In real life, you do not need to do this math — the register does it for you. But if you are checking a receipt or calculating a budget, either approach works.

Sales tax on online and mail orders

Online retailers are required to collect sales tax on orders shipped to your state if the seller has a physical location in your state or meets your state's economic nexus threshold. Most states define economic nexus as a certain amount of sales revenue or number of transactions in that state per year — commonly $100,000 in sales or 200 transactions.

If a seller does not meet that threshold and has no physical presence in your state, they may not collect tax at checkout. However, you are still legally responsible for paying sales tax on that purchase — it is called use tax, and you owe it to your state. Most people do not pay use tax voluntarily, but some states ask you to report it on your income tax return.

When you shop online, the tax is usually calculated and added at checkout based on the shipping address you provide. If no tax appears, check the seller's tax policy or contact them to confirm whether they collect tax in your state.

Understanding tax-inclusive versus tax-exclusive pricing

In the United States, prices displayed in stores are almost always tax-exclusive, meaning the price tag does not include sales tax. You pay the amount shown, plus tax at checkout. This is different from many other countries, where the displayed price includes all taxes.

A few U.S. states and cities have experimented with tax-inclusive pricing for certain items, but it is not standard. When you see a price, assume it is before tax unless the store explicitly states otherwise. This is why your receipt total is always higher than the price tag.

Frequently Asked Questions

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

No. Most states exempt groceries, prescription medications, and some medical equipment. Prepared food, restaurant meals, and alcohol are usually taxed. Services like haircuts and repairs are typically not taxed. The specific exemptions depend on your state's rules.

What if the tax on my receipt does not match my calculation?

Small differences (a few cents) can happen because of rounding. If the difference is larger, check that you used the correct tax rate for your location and that you did not include tax-exempt items in your calculation. You can also ask the store to explain the tax amount.

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

You owe use tax to your home state on out-of-state purchases, but it is rarely enforced for individual shoppers. If you buy something in a state with no sales tax and bring it home, your state may consider it taxable. Check your state's Department of Revenue website for the rules.

Why does the same item cost different amounts in different states?

The item itself costs the same, but the sales tax added to it varies by state and local tax rates. A $50 item costs $53.50 in a 7% tax area but $54.50 in an 8% tax area. Some states also have different exemptions, so groceries might be taxed in one state but not another.

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

Generally, no. Sales tax is final once you pay it. If you return an item, the store refunds the pre-tax price plus the tax you paid. If you believe you were overcharged, contact the store with your receipt.