A sales tax ID number doesn’t have one uniform look. Each state designs its own numbering system, so the format depends entirely on which state issued the permit. Some sales tax IDs are short numeric strings of seven or eight digits; others run to eleven or thirteen. Some mix letters and numbers, some carry a two-letter prefix, and some embed part of the business’s federal EIN. There’s no national standard the way there is for a federal Employer Identification Number.
How the Format Varies by State
Purely numeric IDs are the most common style, but the digit count is all over the map. A permit issued in one state might be a seven-digit number, while a permit issued next door might be thirteen digits. A handful of states break the number into segments with dashes or hyphens, which looks a bit like the format of an EIN but carries no relationship to it.
Alphanumeric formats show up too. Some states add a two-letter prefix that identifies the account type or the jurisdiction, producing an ID that leads with letters and continues with numbers. Other states build part of the business’s federal EIN directly into the state sales tax number, which lets the state agency cross-reference federal filings with state sales tax accounts. And plenty of states assign a completely independent number that bears no resemblance to any federal identifier at all.
Because the systems are so different, two businesses in different states can hold sales tax IDs that look nothing alike. Neither is more “correct” than the other. Whatever number is printed on the certificate the state issued is the sales tax ID for that state, in the format that state uses.
You Can’t Judge a Sales Tax ID by Its Format
The practical consequence of all this variation is that you can’t look at a sales tax ID and tell whether it’s valid based on how it’s arranged. There’s no check digit rule that applies nationwide, no length that’s always correct, and no pattern you can compare against. A number that looks unusual to you may be perfectly standard in the state that issued it.
If you’re a wholesaler or supplier and a customer hands you a resale certificate, don’t try to eyeball the ID number. Verify it. Many states offer free online lookup tools through their tax agency websites where you can enter a sales tax ID and confirm whether it’s active. These tools generally verify only IDs issued by that particular state — they don’t validate out-of-state permits or federal tax numbers. If you accept a resale certificate with an invalid or expired ID and the transaction is later audited, you can be held responsible for the sales tax that should have been collected.
Sales Tax ID vs. Federal EIN
The two numbers get confused all the time, but they’re separate things issued by separate agencies. An EIN is a nine-digit number formatted as XX-XXXXXXX, assigned by the IRS for federal tax purposes like income tax and payroll reporting.1Internal Revenue Service. Understanding Your EIN The XX-XXXXXXX format is fixed and always the same.
A sales tax ID is issued by a state tax agency, and it exists for one purpose: collecting and remitting sales and use tax within that state. Its format is whatever the state decided on. A business can hold an EIN and never need a sales tax ID (if it doesn’t sell taxable goods or services), and a sole proprietor can need a sales tax ID even if they use a Social Security number instead of an EIN for federal filings.2Streamlined Sales Tax. Registration FAQ
So if the number you’re looking at is nine digits in an XX-XXXXXXX pattern, it’s an EIN, not a sales tax ID. Anything else, and you’re likely looking at a state-issued number whose format is set by that state.
Where the Number Appears
After registration, the state issues the sales tax ID number along with a physical or digital document. The document goes by different names depending on the state: certificate of authority, seller’s permit, or sales tax license. The function is the same regardless of the name. The ID number is printed on that document, and most states require you to display the certificate at each location where you make taxable sales.
The same number goes on any resale certificate you give to a supplier when buying inventory tax-free. People sometimes call it a “resale number” or “resale permit,” but it isn’t a separate registration — your sales tax ID is the number that goes on the resale certificate. The certificate is just a form; the ID is what gives it legal weight.
One ID per State
A business selling in multiple states will end up with a separate sales tax ID from each state where it’s registered. Since each state uses its own format, the collection of IDs may look like an unrelated grab-bag of account numbers. That’s normal. What matters is keeping them straight, because you’ll need the correct one every time you file a return or issue a resale certificate in that jurisdiction.
Registration in more than one state has become common because of economic nexus. Since the Supreme Court’s 2018 decision in South Dakota v. Wayfair, states can require registration from businesses that have no physical presence there. The most common threshold is $100,000 in annual sales into the state, though a few states set higher bars at $500,000. Some states also count transaction volume, requiring registration after 200 or more separate sales in a year, though several have recently dropped the transaction test and rely on the dollar threshold alone.3Streamlined Sales Tax. Remote Seller State Guidance An online seller shipping nationwide can trigger registration requirements in dozens of states at once, each generating its own sales tax ID in its own format.
Five states don’t impose a statewide sales tax at all, so a business selling exclusively in those states wouldn’t hold a state sales tax ID from them.
If You Can’t Find Your Number
The sales tax ID is on the certificate of authority or seller’s permit the state issued when you registered. If you’ve misplaced the certificate, most state tax agencies let you log in to their online portal to look up the account number, request a replacement certificate, or download a digital copy. The number itself doesn’t change — it stays attached to the account as long as the account is open and in good standing.
If your business structure changes, you move, or you add locations, you generally have to update the registration with the state, and in some cases that triggers a new ID rather than an amendment to the existing one. And if you buy an existing business, don’t assume you inherit the seller’s sales tax ID. Most states require the new owner to register for a fresh permit, which means a fresh number in whatever format that state uses.