To calculate sales tax for online orders, multiply the taxable portion of your cart by the combined state and local tax rate at your delivery address. That combined rate stacks a state base rate with any county, city, or special-district taxes, and it can range from under 5% to over 10% depending on where the package is going. The math is simple once you have the two inputs; the work is in finding the right rate and knowing which items in your cart are actually taxable.
The Formula
The basic calculation:
Tax owed = Taxable subtotal × Combined tax rate
Say you’re ordering $120 worth of taxable goods shipped to an address with a combined rate of 8.25%. Convert the percentage to a decimal (0.0825), then multiply: $120 × 0.0825 = $9.90 in sales tax. The order total comes to $129.90 before shipping.
If your cart mixes taxable and exempt items, only the taxable items enter the formula. A $120 order where $80 is taxable clothing and $40 is exempt groceries produces: $80 × 0.0825 = $6.60.
Find the Combined Rate for Your Delivery Address
The most important number in the calculation is the combined sales tax rate for the specific address where the order arrives. Most states use destination-based sourcing, meaning the rate is determined by the delivery location rather than where the seller ships from. A handful of states use origin-based sourcing for in-state transactions, but for purchases from out-of-state sellers the destination rule applies almost universally. Two people ordering the same item from the same retailer can owe different amounts of sales tax based solely on where they live.
A combined rate typically stacks two or three layers: a statewide rate, a county rate, and sometimes a city or special-district surcharge funding things like public transit or stadium bonds. The statewide rate is easy to find. The local layers are what catch people off guard. A state with a 6% base rate might have pockets where the combined rate hits 9% or higher once local taxes stack up. Five states (Alaska, Delaware, Montana, New Hampshire, and Oregon) have no statewide sales tax at all, though some localities in Alaska impose their own.
Every state with a sales tax runs a rate lookup tool on its revenue department website. You type in a street address or zip code, and the tool returns the total combined rate for that exact location. These databases reflect current local ordinances and newly approved tax levies, so they’re more reliable than third-party calculators. Use the full street address when possible: zip codes can span multiple tax jurisdictions, and a zip-code-only lookup may return the wrong rate.
Which Items in Your Cart Are Taxable
Not everything gets taxed at the same rate, and some items aren’t taxed at all. States carve out exemptions and reduced rates for certain product categories, and those categories vary widely.
Groceries are the most common example. Many states exempt unprepared food entirely, some tax it at a reduced rate, and others tax it at the full rate. Prepared food, including a deli sandwich or a restaurant order through a delivery app, is almost universally taxable. Prescription medications and medical devices are exempt in most states. Clothing gets more varied treatment: a few states exempt all clothing, others exempt items under a certain dollar amount, and most tax clothing at the standard rate. For high-value apparel it’s worth checking whether your state applies any special rules.
Digital products (streaming subscriptions, e-books, downloaded software) occupy a gray area that has gradually become less gray. A strong majority of states now tax at least some categories of digital goods, though the specifics differ. Some tax downloaded music but not streaming. Others tax all digital products at the full rate. A few still exempt most digital transactions. If your order includes both a physical product and a digital one, they may each carry a different tax treatment within the same checkout.
One timing note: about 20 states hold sales tax holidays each year, most commonly for back-to-school shopping in July or August. During these windows, qualifying items (typically clothing, school supplies, and computers under specified price caps) are exempt from state sales tax and sometimes local taxes too. Price thresholds commonly fall at $100 for clothing, $50 for school supplies, and $1,500 for computers, though each state sets its own limits. These holidays apply to online purchases shipped to that state, so timing a large order around one can save real money.
How Shipping Fits Into the Math
Whether shipping is taxable depends on your state, and the rules are genuinely messy. Roughly two-thirds of states with a sales tax treat delivery charges as taxable to some degree, but the conditions vary. Some tax shipping whenever the underlying product is taxable. Others only tax shipping when the charge isn’t listed separately on the invoice. A few exempt delivery charges entirely.
When shipping is taxable, add it to the subtotal before applying the rate:
Tax owed = (Taxable subtotal + Shipping) × Combined tax rate
For a $100 taxable order with $8.99 shipping in a state that taxes delivery, at a 7.5% rate: ($100 + $8.99) × 0.075 = $8.17 in tax. Most online retailers handle this correctly in their checkout systems, but it explains why the tax line sometimes looks slightly higher than the product prices alone would suggest.
Why Some Checkouts Show No Tax
A seller only collects sales tax from you if they have a legal connection to your state, known as nexus. In 2018 the Supreme Court decided South Dakota v. Wayfair, allowing states to require tax collection from sellers who have no physical presence but do enough business in the state. After that, every state with a sales tax enacted an economic nexus law, generally triggered once a seller crosses a dollar threshold in annual sales within the state. The South Dakota law at the center of the case set the line at $100,000 in gross sales or 200 separate transactions per year, and many states adopted similar thresholds.1Supreme Court of the United States. South Dakota v. Wayfair, Inc. A small independent seller who falls below whatever threshold applies in your state generally won’t collect tax on your order.
Marketplaces work differently. If you buy through Amazon, eBay, Etsy, Walmart’s marketplace, or a similar platform, the platform itself collects the tax, not the individual seller. Every state with a sales tax now requires marketplace facilitators to collect and remit on behalf of their third-party sellers. That’s why you almost always see tax on Amazon orders even when the actual seller is a tiny shop that would never hit the nexus threshold on its own. If you find the same item on that seller’s independent website with no tax at checkout, the seller likely hasn’t crossed the nexus threshold in your state for their off-platform sales.
Use Tax: What You Owe When the Seller Doesn’t Charge
If a seller doesn’t collect sales tax on your order, you generally still owe the equivalent tax to your state. It’s called use tax, it exists in every state with a sales tax, and the rate is identical to the sales tax rate you’d otherwise pay. The obligation falls on you, the buyer, to report and remit it.
In practice, most individuals ignore use tax on small purchases, and states have historically had little ability to enforce it on consumer-level transactions. But the obligation is real. Many states include a use tax line directly on the individual income tax return, and some provide a lookup table based on your income so you can estimate what you owe without tracking every receipt. If you’re audited and untaxed purchases surface, you’ll owe the back tax plus penalties and interest.
Use tax matters most on large purchases. Buying a $2,000 laptop from an out-of-state seller with no nexus in your state at an 8% rate means $160 you technically owe. Whether to self-report on a $15 book is a question of compliance; on big-ticket items, the calculus shifts quickly.
International orders sit outside the sales tax question and bring their own layer of duties, customs fees, and carrier brokerage charges once the de minimis exemption for low-value shipments was suspended in February 2026.2The White House. Continuing the Suspension of Duty-Free De Minimis Treatment for All Countries State use tax can still apply on top of those charges if the overseas seller didn’t collect.
If the Tax Charged Looks Wrong
Run the numbers against the official combined rate for your delivery address using your state’s rate lookup tool. Common causes of overcharges include the retailer applying the wrong jurisdiction’s rate, taxing an exempt item, or including shipping in the taxable base when the state doesn’t require it.
Contact the seller or marketplace first. Most large retailers and platforms will refund overcharged tax once you identify the error. Provide your order confirmation, delivery address, and the correct rate from the state’s lookup tool. If the seller refuses or doesn’t respond, you can file a refund claim with your state’s department of revenue; most states have a consumer process for recovering overpaid sales tax, though it typically requires documentation of the purchase and the specific overcharge. If you had an exemption certificate (for resale, nonprofit status, or similar) and the seller still charged tax, send the certificate directly and request a credit.