Sales Tax Calculator: How It Works
Sales tax is added at the point of sale rather than included in the shelf price across much of North America, which makes the total at the till different from the price on the label. This calculator handles both adding tax and extracting it, plus the combined state-and-local rates that make the arithmetic non-obvious.
Adding and removing
Add: Tax = Price × Rate ÷ 100, Total = Price + Tax.
Remove from a tax-inclusive total: Price = Total × 100 ÷ (100 + Rate).
A 47.99 item at 8.25%: tax = 3.96, total = 51.95. Working backwards from a 51.95 receipt: 51.95 × 100 ÷ 108.25 = 47.99. Subtracting 8.25% from 51.95 would give 47.66 — wrong by 33 cents, and the error scales with the amount.
Rates are stacked, not single
In the United States a quoted rate is usually the sum of several jurisdictions:
| Layer | Typical range |
|---|---|
| State | 0% – 7.25% |
| County | 0% – 2% |
| City / municipal | 0% – 2.5% |
| Special district (transit, stadium, health) | 0% – 2% |
Combined rates commonly land between 6% and 10%, and exceed 10% in some localities. Five states levy no statewide sales tax at all — Alaska, Delaware, Montana, New Hampshire and Oregon — though Alaska permits local sales taxes. Rates change, so verify the current combined rate for the specific address rather than the state.
Origin versus destination sourcing
For remote and online sales, most states apply destination-based sourcing: the rate is the buyer's location, not the seller's. A handful use origin-based sourcing for intrastate sales. This is why an online cart's tax changes when you change the shipping address, and why sellers shipping nationwide must handle thousands of rate combinations rather than one.
Economic nexus
Since the 2018 South Dakota v. Wayfair decision, a state can require an out-of-state seller to collect sales tax once the seller crosses a threshold of sales into that state — commonly 100,000 in revenue or 200 transactions per year, though thresholds vary and several states have dropped the transaction test. Physical presence is no longer required. Marketplace facilitator laws shift the obligation to the platform for sales made through it, which is why a marketplace often collects tax even when the individual seller is below any threshold.
What is commonly exempt
- Groceries — fully exempt in many states, taxed at a reduced rate in some, fully taxed in a few. Prepared food is almost always taxed even where groceries are not.
- Prescription medicine — generally exempt; over-the-counter treatment varies.
- Clothing — exempt in a small number of states, sometimes only below a price threshold per item.
- Services — historically untaxed in many states, though this is steadily narrowing.
- Resale purchases — exempt with a valid resale certificate, since the tax is collected at the final sale.
Sales tax holidays
Many states suspend tax on specific categories for a few days each year — commonly school supplies, clothing under a price cap, computers, or emergency preparedness goods. The eligible items, price caps and dates are defined narrowly, so a laptop may qualify while its case does not.
Sales tax versus VAT and GST
Sales tax is charged once, at the final retail sale to the consumer, and businesses buying for resale are exempt. VAT and GST are charged at every stage of the chain, with businesses reclaiming the tax on their inputs. The economic result is similar; the compliance burden and the invoice mechanics are very different.