Sales Tax Calculator Guide: Add Tax, Reverse Tax & State Rates
Learn how sales tax is added to a purchase, how to reverse-calculate the pre-tax price from a total, and why state and local rates can change the result.
Sales tax is a percentage-based charge added to many purchases. The rate may include state, county, city, and special district components, which is why the same item can cost different amounts in different locations.
A sales tax calculator is useful for two common tasks: adding tax to a pre-tax price and reversing tax from a total price to estimate the original pre-tax amount.
How Sales Tax Works
Sales tax is generally applied as a rate multiplied by the taxable price. If the taxable price is $100 and the sales tax rate is 7%, the tax is $7 and the total is $107.
Not every purchase is taxable in the same way. Some states exempt groceries, clothing, medication, or other categories. Local rates and product rules can also vary.
How to Add Sales Tax
To add tax to a price, convert the tax rate to a decimal, multiply by the pre-tax price, and add the tax amount to the original price.
Total = 240 + 18 = 258
Result: $258.00
How to Remove Sales Tax
Reverse sales tax starts with the total price and works backward to estimate the pre-tax amount.
Tax amount = 258 − 240 = 18
Result: $240 pre-tax price and $18 tax
Why Rates Vary by State
Sales tax rates vary because states and local governments set their own rules. Some states have no statewide sales tax, while others combine state and local rates. The final rate may depend on the delivery address, store location, product type, and local tax district.
Use the main Sales Tax Calculator for add-tax and reverse-tax math, or browse state-specific pages such as the California Sales Tax Calculator, Texas Sales Tax Calculator, and Florida Sales Tax Calculator.
Common Use Cases
- Retail purchases: estimate the final checkout total before paying.
- Budgeting: compare what a purchase will actually cost after tax.
- Receipts: back into the pre-tax price from a total amount.
- Small business estimates: model customer-facing totals before invoicing or point-of-sale setup.
- State comparisons: see how different state-level rates change the same purchase amount.
Frequently Asked Questions
How do I calculate sales tax?
Multiply the taxable price by the sales tax rate expressed as a decimal. For example, 100 dollars at 7% tax produces 7 dollars of tax.
How do I remove sales tax from a total?
Divide the total price by 1 plus the tax rate. For example, 107 dollars divided by 1.07 equals 100 dollars before tax.
Why is sales tax different by state?
Sales tax rates vary because states, counties, cities, and special districts can set different rules and rates.
Can I use the calculator for state-specific sales tax?
Yes. Use the main Sales Tax Calculator for general math or the state-specific sales tax calculators for state-focused pages.
Add tax to a price, remove tax from a total, and compare state-specific sales tax calculator pages.
Open Sales Tax Calculator →