The Basic Formula for Sales Tax

Sales tax is calculated by taking the price of what you buy and multiplying it by the tax rate for your location. The formula is: Purchase Price × Tax Rate = Sales Tax Amount. Then you add that tax to the original price to get your total cost at checkout.

For example, if you buy an item for $100 in a place with a 7% sales tax rate, you multiply $100 by 0.07 to get $7 in tax. Your total cost is $107. The tax rate changes depending on which state, county, or city you are in — there is no single rate across the country.

Most stores calculate this automatically at the register or checkout, so you do not have to do the math yourself. But understanding how it works helps you know what you will actually pay before you reach the counter.

Key Takeaways

  • Multiply the item price by the tax rate (shown as a decimal) to find the tax amount, then add it to the original price.
  • Sales tax rates vary by state and sometimes by county or city within a state, so the same item costs different amounts in different places.
  • Not all items are taxed the same way — groceries, medicine, and clothing may be taxed at lower rates or not taxed at all depending on your state.
  • Online purchases are taxed based on where the item ships to, not where the seller is located, though some online retailers may not charge tax.
  • You can find your local tax rate through your state's tax department website or by asking a store in your area.

Converting the Tax Rate to a Decimal

Tax rates are usually shown as a percentage, but to do the math you need to convert that percentage to a decimal. If your tax rate is 8%, you move the decimal point two places to the left to get 0.08. A 6.5% rate becomes 0.065. A 10% rate becomes 0.10.

Once you have the decimal, multiply it by the price. A $50 item in an 8% tax area costs $50 × 0.08 = $4 in tax, for a total of $54. A $200 purchase in a 6.5% tax area costs $200 × 0.065 = $13 in tax, for a total of $213.

Why Tax Rates Differ by Location

Each state sets its own sales tax rate, and that rate can range from 0% (in states like Oregon, Montana, New Hampshire, and Delaware) to over 7%. But the rate you pay is not just the state rate — it often includes county and city taxes added on top.

For example, Colorado's state sales tax is 2.9%, but Denver adds 3.62%, bringing the total to 6.52%. In Tennessee, the state rate is 4%, but some counties add up to 2.75%, so the total can reach 6.75%. This means two stores in the same state can have different tax rates depending on which county or city they are in.

You can find your exact local rate by searching "[your city] sales tax rate" or by visiting your state's Department of Revenue website. Most states list rates by county and sometimes by city.

Items That May Be Taxed Differently

Not everything you buy is taxed at the standard rate. Many states do not tax groceries, or tax them at a lower rate than other goods. Medicine and medical equipment are often untaxed or taxed at a reduced rate. Some states do not tax clothing, or only tax clothing above a certain price.

The rules vary widely. In New York, groceries are not taxed, but in California they are. In Pennsylvania, clothing under $110 is not taxed, but clothing above that is. Some states tax prepared food differently than raw ingredients.

When you are shopping, the store's system knows which items fall into which category and applies the correct rate automatically. If you want to know whether a specific item is taxed in your state, your state's tax department website usually has a list of what is and is not taxed.

Calculating Tax on Multiple Items

When you buy several items, you can calculate the tax two ways. The first way is to add up all the prices, then multiply the total by the tax rate. If you buy a $30 shirt, a $20 pair of pants, and a $15 hat, your subtotal is $65. At 7% tax, you owe $65 × 0.07 = $4.55 in tax, for a total of $69.55.

The second way is to calculate tax on each item separately, then add all the taxes together. This gives the same answer: ($30 × 0.07) + ($20 × 0.07) + ($15 × 0.07) = $2.10 + $1.40 + $1.05 = $4.55. Stores use the first method because it is faster, but both are correct.

If some items are taxed at different rates — for example, if groceries are not taxed but other items are — you separate them into groups, calculate tax on each group at its rate, then add everything together.

Sales Tax on Online and Mail Orders

Online purchases are taxed based on where the item is being shipped, not where the seller is located. If you order something online to be delivered to an address in Texas, Texas sales tax applies, even if the seller is in a state with no sales tax.

However, not all online sellers charge sales tax. Large retailers like Amazon and Walmart charge tax on most items, but some smaller sellers may not, depending on their size and where they are based. The rules changed in 2018 to require more online sellers to collect tax, but enforcement varies.

When you check out online, the tax is usually calculated and shown before you complete your purchase, so you know your final cost. If you do not see tax added and you are ordering to a state that has sales tax, contact the seller to ask whether tax will be added.

Frequently Asked Questions

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

No. Most states do not tax groceries, prescription medicine, or medical devices. Some states do not tax clothing. A few states have no sales tax at all. The items that are taxed and the rate depend on your state and sometimes your county or city.

What if the price tag does not match what I pay at checkout?

The difference is almost always sales tax. Price tags show the item's price before tax. At checkout, the store adds the sales tax for your location. If the total seems wrong, ask the cashier to show you the breakdown of price and tax.

Can I get sales tax back if I return an item?

Yes. When you return an item, the store refunds both the item price and the tax you paid on it. The refund appears as the full amount you paid, including tax.

Is sales tax the same everywhere in my state?

No. Most states have different rates in different counties or cities. Two stores in the same state can charge different tax rates. You can find your exact local rate by searching your city name and "sales tax rate" or by checking your state's tax department website.

How do I know what tax rate to use when I am shopping online?

The online store's checkout page automatically calculates tax based on the address you enter for delivery. You do not need to look up the rate yourself — it will be shown in your order summary before you pay.