A sales tax ID number is a state-issued identifier that authorizes your business to collect sales tax from customers on taxable purchases and remit it to the state. Any business making taxable sales in a state that imposes a sales tax needs one before its first transaction there, and you may need a separate one in every state where you have a tax obligation. The rules around when the obligation kicks in, what the credential is called, and what happens if you skip it are where most of the confusion lives.
What the Number Actually Is
A sales tax ID is a unique number your state’s taxing authority assigns when you register to collect sales tax. It ties your business to the state’s tax system so you can collect, report, and remit the correct amount on each filing cycle.
It is not the same as your federal Employer Identification Number. An EIN identifies your business to the IRS for federal purposes and works nationwide. A sales tax ID is state-specific and only authorizes collection of that state’s sales and local taxes. Businesses operating across state lines often hold one EIN and several sales tax IDs.
The name on the credential varies by state. You may see it called a Seller’s Permit, a Sales Tax License, a Certificate of Authority, or a Sales and Use Tax Permit. All of them do the same job: confirm that your business is registered with the state and legally permitted to charge customers sales tax at checkout.
Who Needs to Register
Your obligation to register in a given state depends on whether you have “nexus” there. Nexus is just a sufficient connection to the state that triggers a legal duty to collect its sales tax. There are two flavors.
Physical Nexus
Physical nexus is the traditional test. If your business has a tangible presence in a state, you have nexus there. That includes an office, a retail store, a warehouse, inventory stored at a fulfillment center, employees working in the state, or sales reps attending trade shows. Every state with a sales tax recognizes physical presence as a nexus trigger.
Economic Nexus
Economic nexus is the newer standard, established by the U.S. Supreme Court’s 2018 decision in South Dakota v. Wayfair, Inc.1Oyez. South Dakota v. Wayfair, Inc. The Court overturned the older physical-presence requirement and held that states can require tax collection from remote sellers who do a significant volume of business in the state, even with no physical footprint there.
The most common threshold is $100,000 in gross sales into a state during the current or prior calendar year. Some states also trigger nexus at 200 separate transactions, though that count has been shrinking. As of early 2026, only about 16 states still use a transaction-count threshold; most have moved to a sales-dollar-only test.
Once you cross either the physical or economic threshold in a state, you are required to register and start collecting. Waiting until someone notices is not a viable plan, since states routinely share data with marketplace platforms and payment processors to identify unregistered sellers.
What Counts as a Taxable Sale
Registration is not just for businesses selling physical products. Many states tax certain services, digital goods, and software subscriptions, and the categories vary enormously. Some states tax almost no services; others tax dozens of categories including landscaping, dry cleaning, security services, interior design, and gym memberships. Software-as-a-service is taxable in a growing number of states. If you sell services or digital products, check taxability in each state where you have nexus before assuming you are exempt.
The Five States Without a Sales Tax
Alaska, Delaware, Montana, New Hampshire, and Oregon do not impose a statewide sales tax, so businesses operating exclusively in those states do not need a state sales tax ID for this purpose. Alaska is a partial exception because some local jurisdictions within the state levy their own sales taxes, which may require local registration. If you sell into other states, the nexus rules above still apply to those out-of-state sales.
Selling Through a Marketplace
If you sell through Amazon, Etsy, eBay, or a similar platform, you may not need to collect sales tax on those transactions yourself. Every state with a sales tax now has a marketplace facilitator law that shifts the collection and remittance responsibility from the individual seller to the platform for sales made through it. The marketplace calculates the tax, charges the customer, and sends the money to the state.
That does not always mean you can skip registration. Some states still require marketplace sellers to hold their own sales tax permit even when the platform is collecting on their behalf. And if you also sell through your own website or at craft fairs, you are responsible for collecting tax on those direct sales. The marketplace facilitator law only covers transactions that flow through the platform.
In most states, the platform bears the audit liability for tax it was supposed to collect, unless the error traces to incorrect information you provided. The safest approach is to register in any state where you have nexus, regardless of whether a marketplace is handling some of your sales.
How to Register
Registration happens through the state’s Department of Revenue, Department of Taxation, or equivalent agency. Almost every state offers online registration through a taxpayer portal, and the process takes anywhere from a few minutes to a few business days.
Have this information ready:
- Legal business name, any trade names, physical address, and mailing address.
- Your EIN, or your Social Security Number if you are a sole proprietor without an EIN.
- Your business structure: sole proprietorship, partnership, LLC, or corporation.
- Names, addresses, and sometimes Social Security Numbers for all principal officers, partners, or members.
- Expected monthly or annual sales volume, which the state uses to assign your initial filing frequency.
- The date you began or plan to begin making taxable sales in the state.
After approval, the state issues your sales tax ID along with a formal permit or certificate. Many states require you to display this document at your business location.
What Registration Costs
Most states issue sales tax permits for free. A handful charge a small registration fee, running from zero to about $100 per location. Some states also require a refundable security deposit or surety bond, particularly for new businesses or those with a history of tax issues, which can range from a few hundred to several thousand dollars. Check with your specific state before registering so the cost does not catch you off guard.
Registering in Several States at Once
If you need to register in multiple states at the same time, the Streamlined Sales Tax Registration System (SSTRS) can consolidate the paperwork. This free system lets you register for sales tax in all 24 participating member states through a single online application.2Streamlined Sales Tax. Sales Tax Registration SSTRS Participating states include Georgia, Indiana, Michigan, New Jersey, North Carolina, Ohio, Washington, and Wisconsin, among others. You still file returns and pay tax directly to each state, but the registration step becomes one form. For non-member states, you register individually through each state’s own portal.
What You Use the Number For
Once you have the number, it appears on every return you file, every resale certificate you issue, and every piece of correspondence with the state taxing authority.
Collecting the Right Rate
Sales tax rates are rarely a single state percentage. Most transactions are taxed at a combined rate that includes the state rate plus any county, city, or special district taxes. One state can have hundreds of different combined rates depending on the delivery address. Getting this wrong is one of the most common compliance failures for businesses shipping to many locations.
Buying Inventory Tax-Free
Your sales tax ID also lets you buy inventory for resale without paying sales tax on the purchase. You give your supplier a resale certificate that includes your sales tax ID number, certifying that you intend to resell the goods. The supplier then sells to you tax-free, and tax gets collected only when the end customer buys the product. Misusing a resale certificate for personal purchases or non-resale business expenses is taken seriously by state auditors and can result in back taxes, penalties, and interest.
Exemption Certificates from Buyers
Your number is also relevant when you sell to exempt purchasers. Nonprofit organizations, government agencies, agricultural operations, and manufacturers purchasing raw materials often present exemption certificates to avoid tax on qualifying purchases. As the seller, you are responsible for collecting and retaining valid exemption certificates from these buyers. If you cannot produce one during an audit, the state will hold you liable for the uncollected tax.
Filing Returns
The state assigns your filing frequency based on how much tax you collect. Higher-volume businesses typically file monthly, mid-range businesses file quarterly, and very small sellers may file annually. These assignments are not permanent; the state can move you to a more or less frequent schedule as your sales change.
You must file a return for every assigned period, even if you made zero sales and owe no tax. Skipping a “zero return” is treated the same as failing to file. Keep detailed records of every sale, the tax collected, exemption certificates received, and resale certificates issued. Most states require you to retain these records for at least three to four years from the date the return was filed or the tax was due, whichever is later. The IRS recommends keeping business tax records for at least three years as a general baseline.3Internal Revenue Service. How Long Should I Keep Records?
What Happens If You Skip Registration
Selling taxable goods or services without a valid permit is not a gray area. States treat it as a serious compliance failure.
Penalties commonly include the full amount of uncollected tax you should have charged, interest on that amount (often at double-digit annual rates), and additional civil penalties that can reach thousands of dollars. Some states impose a per-day fine for each day you operate without a permit. In states that treat willful non-compliance as a criminal matter, you could face misdemeanor charges carrying fines and even jail time.
Officers and partners of a business entity can also be held personally liable for unpaid sales tax. This is one of the few areas where the corporate liability shield does not fully protect owners. If your LLC or corporation fails to collect and remit sales tax, the state may come after you individually for the balance, plus interest and penalties.
Late filing and late payment carry their own penalties even when you are properly registered. Most states charge a percentage-based penalty on the unpaid tax plus interest for each month the return or payment is overdue.
Renewals, Transfers, and Closing Down
In most states, your sales tax permit stays valid indefinitely as long as you keep filing returns and staying current on payments. A few states require periodic renewal. Colorado, for example, requires businesses to renew their sales tax license every two years and charges a $16 fee per location.4Department of Revenue – Taxation. Renew Your Sales Tax License Missing a renewal deadline means your permit expires and you are operating without a license until you fix it.
Sales tax permits generally cannot be transferred to a new owner. If you sell your business, the buyer needs to apply for their own permit. As the seller, confirm all outstanding returns are filed and all tax is paid before the transfer closes, since unpaid liabilities can follow the business assets in many states.
When you close your business or stop making taxable sales in a state, do not just stop filing. Formally close your sales tax account with the state, which usually involves filing a final return covering your last period of activity and then submitting a closure request through the state’s online portal or in writing. Leaving an account open means the state will keep expecting returns, and missing those returns generates penalties automatically.