How to Use a Sales Tax Calculator for Any State
A guide to finding the correct sales tax rate, adding tax to a price, working backwards from a total, and calculating sales tax on online purchases.
Finding the Correct Sales Tax Rate
Sales tax rates in the United States vary by state, county, and city. The rate you need is the combined rate for the specific location where the sale takes place — or, for online purchases shipped to you, the combined rate for your delivery address.
State tax authority websites publish current tax rate tables. Most states provide searchable databases where you can enter a zip code or city and find the combined state, county, and city rate. The Tax Foundation also maintains a regularly updated map and database of combined rates by jurisdiction.
When using a sales tax calculator, enter the full combined rate for your location rather than just the state rate. Using only the state rate will understate your actual tax if your county or city also has a local rate. The combined rate is the number that matters for your actual purchase.
Adding Sales Tax to a Price
To add sales tax to a pre-tax price, multiply the price by the tax rate expressed as a decimal and add the result to the original price. A $200 purchase with a 7.5% combined tax rate: multiply $200 by 0.075 to get $15, then add to $200 for a total of $215.
Alternatively, multiply the pre-tax price by one plus the rate: $200 times 1.075 equals $215 directly, which is the same result with one fewer step.
When budgeting for a large purchase, calculate the tax before you shop so you know the true out-of-pocket cost. A $1,500 appliance in a 9% tax location costs $1,635 including tax — the $135 in tax is significant enough to affect your budget decision. Running the calculation in advance prevents surprises at checkout.
Working Backwards From a Total Price
If you see a total price and want to know how much of it is tax, divide the total by one plus the rate to find the pre-tax price, then subtract to find the tax amount.
Example: you paid $107.50 at a store in a location with a 7.5% tax rate. Divide $107.50 by 1.075 to get $100. The pre-tax price was $100 and the tax was $7.50.
This reverse calculation is useful when comparing prices across jurisdictions. An item priced at $107.50 all-in at one store versus $103.00 all-in at another store in a different tax location — working backwards from each total reveals the pre-tax prices and helps you make an accurate comparison.
State vs Local Sales Tax
The sales tax rate you encounter is nearly always a combination of a state rate and one or more local rates. The state portion funds state government services. The local portion — county, city, special district — funds local services and often specific voter-approved projects.
Some jurisdictions have surprisingly complex rate structures. In some major cities, there are overlapping layers: state, county, city, and special transit district taxes all add together. Being aware of this helps you understand why the combined rate is higher than the state rate alone.
When traveling between states, you will notice the rate changes immediately at the border. This affects large purchases significantly. Someone buying a $20,000 car in a state with 8% tax pays $1,600 in sales tax. The same car in a neighboring state at 4% costs only $800 in tax — a $800 difference for the same vehicle.
Sales Tax on Online Purchases
Since the 2018 South Dakota v. Wayfair Supreme Court decision, online retailers are required to collect sales tax in states where they have sufficient economic presence, called economic nexus. This effectively ended the era when many online purchases were tax-free. Most major online retailers now collect tax in all states that have a sales tax.
The rate applied to an online purchase is determined by the destination — your shipping address — not the seller's location. If you live in a city with a 9% combined rate and order from an online retailer, the retailer should charge 9% on your purchase.
For online marketplaces like Amazon or eBay with many third-party sellers, the platform typically handles sales tax collection and remittance on behalf of sellers in states where marketplace facilitator laws apply. You should see tax collected at checkout. If you are not charged tax on a taxable item from an online retailer, technically you owe use tax to your state — though enforcement for individuals is rare, it is a real legal obligation in most states.