How to Calculate Sales Tax
Sales tax is a percentage of a pre-tax price, added at the point of sale. This guide shows the formula, a worked example, and how to estimate sales tax before you buy — using any rate, with no location-specific tax tables.
Last reviewed: 2026-08-19
Sales tax formula
- Tax Amount = Price × (Tax Rate ÷ 100)
- Final Total = Price + Tax Amount
The tax rate is always a percentage of the pre-tax price. Convert it to a decimal (8% becomes 0.08) before multiplying. The final total is simply the price plus the tax amount. Try your own numbers with the Sales Tax Calculator.
Worked example
Suppose an item costs $100 before tax and the applicable rate is 8%.
- Tax = $100 × (8 ÷ 100) = $8
- Total = $100 + $8 = $108
The same arithmetic works for any price and any rate. A $250 item at 6.5% has a tax amount of $250 × 0.065 = $16.25 and a total of $266.25.
How to calculate sales tax step by step
- Find the pre-tax price of the item.
- Identify the sales tax rate that applies where the sale takes place.
- Convert the rate to a decimal by dividing by 100.
- Multiply the pre-tax price by that decimal to get the tax amount.
- Add the tax amount to the pre-tax price to get the final total.
Decimal rate conversion
Rates are written as percentages but used as decimals. Divide the percentage by 100: 5% becomes 0.05, 7.25% becomes 0.0725, 0% becomes 0. A rate of 0% means no sales tax applies, so the tax amount is zero and the total equals the price.
Calculating sales tax on multiple quantities
When you buy several identical items, find the pre-tax subtotal first, then apply the rate. For 4 items at $30 each with a 7% rate:
- Subtotal = $30 × 4 = $120
- Tax = $120 × 0.07 = $8.40
- Total = $120 + $8.40 = $128.40
Multiplying the unit price by the quantity and then by the rate gives the same tax amount; grouping the subtotal first keeps the working readable.
How to estimate sales tax before a purchase
To estimate sales tax before checking out, take the listed price and multiply it by the rate as a decimal. A $60 item in an area with a 6.5% rate has an estimated tax of about $3.90 and an estimated total of about $63.90. The estimate is only as accurate as the rate you use, so confirm the rate for the specific location and product — rates can change and may differ by category.
Tax amount vs final total
The tax amount and the final total are different numbers and people sometimes read the wrong one. The tax amount is the dollar value of the tax alone; the final total is what you actually pay, including the tax. If a receipt shows a tax amount of $8 on a $100 item, the final total is $108 — not $100 or $8.
Common mistakes
- Applying the rate to the total. If a total already includes tax, you cannot find the tax by multiplying the total by the rate. See how to remove sales tax from a total for the correct reverse calculation.
- Forgetting to convert the percentage. Multiplying by 8 instead of 0.08 gives a tax eight times too large. Always divide the percentage by 100 first.
- Using the wrong rate. Rates vary by location and sometimes by product category. Confirm the rate for the specific sale rather than assuming.
- Confusing tax with a discount. A discount reduces the price before tax; sales tax is added after. Run both with the Discount Calculator and the Sales Tax Calculator.
For value-added tax, which works on a similar percentage basis, use the VAT Calculator; for general percentage work, the Percentage Calculator.