Sales tax is the tax system small businesses meet earliest and understand last. Unlike income tax, it is transactional: the state authorizes you to collect it (the seller's permit), expects you to collect it correctly on every taxable sale, and treats the collected money as its own from the moment it hits your account. The permit itself is easy; knowing where you owe one, and keeping up with the filing rhythm afterward, is the actual work.
Nexus Decides Where You Register
You need a permit in every state where you have nexus, the legal connection that lets a state tax you. Two kinds matter:
Physical nexus is presence: your location, employees, inventory (including inventory a marketplace stores for you in its warehouses), regular in-person sales, even trade show attendance beyond thresholds in some states. Your home state is always on the list.
Economic nexus arrived with the Supreme Court's decision in South Dakota v. Wayfair on 21 June 2018, which removed physical presence as the constitutional requirement for a state to impose a collection duty. Enough sales into a state now creates the obligation on their own. What counts as enough is set state by state, and the widely repeated shorthand of $100,000 or 200 transactions has been out of date for years in several of the states people quote it about. Cross a threshold and registration is due, usually within a defined window. The full mechanics are in sales tax nexus explained.
The practical sequence for a new seller: register at home before the first sale, then monitor out-of-state revenue by state and register as thresholds approach. Waiting until a state finds you converts a free registration into a back-tax assessment.
The Thresholds Are Not the Same Everywhere
Four states worth reading directly, because they are the ones most often quoted from memory and three of the four do not say what the shorthand says.
South Dakota, the state that brought the Wayfair case, no longer has a transaction test at all. Senate Bill 30 removed it with effect from 1 July 2023, and the Department of Revenue now states that only remote sellers with more than $100,000 in gross sales into South Dakota in the previous or current calendar year must be licensed. A seller with 900 small orders and $40,000 of revenue has no South Dakota obligation, where before July 2023 it did.
California uses $500,000 in total combined sales of tangible personal property for delivery in the state during the preceding or current calendar year, with no transaction count. Texas uses a safe harbour of $500,000 in total Texas revenue in the preceding twelve calendar months, also with no transaction count, and a seller below that is not required to hold a permit or collect. New York is the outlier in the other direction: it requires more than $500,000 of receipts from sales of tangible personal property delivered into the state and more than 100 such sales, measured over the immediately preceding four sales tax quarters. Both tests, not either.
The lesson is not that these four matter more than the others. It is that a single number cannot carry the answer for 45 states plus the District of Columbia, and a compliance calendar built on one will be wrong in both directions: registering where you did not have to, and missing the state where you did. Track revenue by destination state and read that state's own page before you register.
Registration cost varies too and is rarely the deciding factor. California's tax agency describes its online registration as free. Where a state does charge, it is generally a modest fee and sometimes a security deposit, and none of it is comparable to the cost of the ongoing filing calendar. Where the entity itself owes a recurring state charge for existing, that is a different obligation entirely; see franchise tax by state.
Marketplace Facilitator Laws Changed the Math
Every state with a sales tax now has a marketplace facilitator law: Amazon, Etsy, eBay, Walmart, and similar platforms must collect and remit sales tax on your marketplace sales themselves. For pure marketplace sellers this removes most collection work, with two caveats that catch people. First, several states still require the seller's own registration (and returns reporting marketplace sales as excluded) once nexus exists, particularly where FBA inventory creates physical nexus. Second, the moment you add a direct channel (your own site), collection on those sales is entirely yours. Mixed-channel sellers live in both worlds and should map obligations per state rather than assume the platform covers everything.
Compliance monitoring
If you would rather not do this yourself, we track every deadline for your entity and file on time, in every state where you are registered. Or keep reading and file it on your own. This guide covers everything you need either way.
Registering, Then Operating
Two operating details deserve emphasis. Destination sourcing: most states tax by the buyer's location for remote sales, which is why rate automation built into checkout and accounting beats manual tables. And the trust fund principle: collected sales tax is the state's money in your custody, in the same personal liability category as payroll withholding. It is never working capital, and the same logic that makes a responsible person personally assessable for unremitted payroll tax under the federal 941 and 940 rules runs through most state sales tax statutes.
Registration also needs the entity and the federal number in place first. Most state applications ask for the legal entity name exactly as filed, the formation date, the responsible officer, and the EIN. Applying with a trading name that does not match the state record is the most common cause of a rejected application, and the fastest way to lose a fortnight at the point where you are already over a threshold. Reconciling collected tax back to the ledger every period is a bookkeeping discipline rather than a tax one, and it is what makes the return itself a fifteen minute job.
The Mistakes That Generate Assessments
Mistake 01: Selling first, registering later
Why it happensThe permit feels like paperwork that can follow revenue.
ConsequenceUncollectable back tax paid from margin, plus penalties for unpermitted sales.
PreventionRegister at home before the first taxable sale; it is free almost everywhere.
Mistake 02: Ignoring economic nexus while growing
Why it happensOut-of-state sales accumulate quietly under many state thresholds.
ConsequenceMulti-state back-tax exposure discovered years later, often at diligence time.
PreventionTrack sales by state quarterly; register as thresholds approach.
Mistake 03: Skipping $0 returns
Why it happensNo sales, so surely no filing.
ConsequenceLate-filing penalties on empty returns, and eventually permit revocation.
PreventionEvery assigned period gets a return; automate or calendar them.
Mistake 04: No exemption certificates on file
Why it happensWholesale buyers say "we're exempt" and the invoice goes out untaxed.
ConsequenceThe auditor assesses you for every undocumented exempt sale.
PreventionCertificate collected before the first untaxed sale, renewed on the state's cycle.
Mistake 05: Working from the 200-transaction rule of thumb
Why it happensThe Wayfair headline figures, $100,000 or 200 transactions, were repeated so widely that they became the answer for every state.
ConsequenceTwo errors at once: registering in states whose transaction test no longer exists, including South Dakota since July 2023, and missing states with a different dollar figure entirely, such as the $500,000 used by California and Texas.
PreventionKeep a per-state threshold table sourced from each revenue agency, and re-check it annually rather than trusting a summary.
Mistake 06: Assuming the marketplace covers everything
Why it happensFacilitator laws genuinely do move collection to the platform, so the seller sees tax being collected and stops looking.
ConsequenceDirect-channel sales collected nothing, and in states where platform-stored inventory creates physical nexus the seller's own registration was required from the first unit stored.
PreventionMap obligations per state and per channel, and treat the day you launch a direct site as a nexus event in every state you already sell into.
Three Sellers in Practice
The three below are composites of sellers in this position. The state thresholds and dates are the real ones; the business facts are illustrative.
Example 1: Foxglove Ceramics, Etsy plus its own site
A Texas maker sells on Etsy (facilitator collects) and her own site (she collects). She registers in Texas pre-launch, configures destination-based rates at checkout, and watches state-by-state totals quarterly. When California direct sales approach the threshold, she registers there before crossing it.
Outcome: Zero assessments, because registrations preceded obligations. The entire system ran on one quarterly review.
Example 2: Kestrel Supply Co. and the South Dakota transaction test
A Nashville hardware seller ships small orders nationwide. In 2022 it registered in South Dakota because it had crossed 200 separate transactions there on about $38,000 of revenue, and it has filed monthly returns ever since. The transaction test was removed with effect from 1 July 2023, and the state's remaining test is more than $100,000 of gross sales. On its current volume the company has no South Dakota registration requirement at all, and has spent three years filing returns it did not need to file. Deregistering is a decision to take carefully, since it has been collecting tax from South Dakota customers and that money is the state's either way, but the underlying point stands: thresholds move, and nobody writes to tell you.
Outcome: Three years of unnecessary monthly filings, caught only on an annual review of each state's own guidance rather than a summary table.
Example 3: Halcyon Bath Goods approaches $500,000 in California
A Chicago direct-to-consumer brand tracks sales by destination monthly. California receipts run at roughly $34,000 a month, so the $500,000 threshold arrives around month fifteen of the current run rate. The finance lead registers in month thirteen rather than waiting for the crossing, configures destination-based rates including district taxes, and starts filing on the frequency the state assigns. Registering two months early costs the filing effort for two periods. Registering two months late would have meant collecting nothing on roughly $68,000 of taxable sales and paying the tax on them out of margin, since you cannot go back to customers for it. At a combined rate near 9% that is about $6,100 of pure margin, before penalties and interest.
Outcome: The registration preceded the obligation, so no month was ever sold untaxed. The only cost was two extra returns.
What Happens When You Sell Without a Permit
Sales tax has a feature that makes late discovery unusually painful: you cannot go back and collect it. Income tax assessed late is tax you always owed on money you always had. Sales tax assessed late is tax you were supposed to add to somebody else's invoice, and that invoice was settled a year ago. The assessment comes out of margin.
Work the arithmetic on a mid-sized case. A seller crosses a state's threshold in March and registers eighteen months later after a nexus questionnaire arrives. Sales into that state over the unregistered period were $600,000. At a combined state and local rate of 8%, the tax that should have been collected is $48,000. None of it was, so all of it is paid from the seller's own money, before the penalty and interest the state adds on top. On a business running a 12% net margin, that single assessment consumes the profit on $400,000 of sales.
Two smaller numbers matter as well. A $0 return skipped in a state that assigned you monthly filing typically attracts a minimum late-filing penalty in the tens of dollars per period, which is trivial once and meaningful across twelve periods and four states, and repeated non-filing leads to permit revocation. And an undocumented exempt sale is assessed as a taxable one: $180,000 of wholesale shipments with no resale certificates on file at an 8% rate is a $14,400 assessment for a paperwork failure on sales that were genuinely exempt.
The pattern in all three is the same. The cost is never the registration, which is free or close to it in most states. The cost is the interval between the obligation starting and the registration happening, and the only control you have over that interval is knowing where your sales are going. That is why the quarterly review by destination state is the whole discipline, and why a business that is also weighing entity structure should read what is an LLC and LLC taxes alongside this: the sales tax obligation follows the selling activity, not the tax classification, and it exists whether the business is a sole proprietorship, an LLC or a corporation.
Register where nexus lives, file every period, never spend the tax
The permit is the easy part. The discipline is knowing where your sales create nexus, filing on every assigned date including the empty ones, and treating collected tax as the state's money from the moment of sale.
Frequently asked questions
What is a seller's permit?
The state registration (also called a sales tax permit, sales and use tax license, or resale license depending on the state) that authorizes a business to collect sales tax from customers and remit it. It is required before making taxable sales in a state where you have nexus, and registration is free or cheap in most states.
Do I need a seller's permit for an online business?
Yes, wherever you have nexus: always your home state, plus any state where your sales cross that state's economic nexus threshold. The thresholds differ. South Dakota uses more than $100,000 of gross sales and dropped its 200-transaction test in 2023; California and Texas use $500,000; New York requires more than $500,000 and more than 100 sales. If you sell only through marketplaces like Amazon or Etsy, facilitator laws shift most collection to the platform, but some states still require your own registration.
How much does a sales tax permit cost?
Free in most states; the exceptions charge modest fees (commonly $5 to $100, and a few require deposits). The real cost is the ongoing obligation: collecting correctly, filing on the state's assigned frequency even for $0 months, and keeping exemption certificates for wholesale sales.
What is the difference between a seller's permit and a resale certificate?
The permit lets you collect tax from your customers. A resale certificate is what you hand your suppliers to buy inventory tax-free, because tax will be collected on the final sale. You generally need the permit first; the certificate quotes its number. Using resale certificates for non-resale purchases is a fast route to an audit.
What happens if I sell without a permit?
States assess the uncollected tax against you personally plus penalties and interest, and selling without a permit is itself an offense in most states. Since you cannot retroactively collect from past customers, the tax comes out of your margin. Registering late is always cheaper than being found.
How often do I file sales tax returns?
The state assigns monthly, quarterly, or annual frequency based on your volume, and adjusts it as you grow. Returns are due even for zero-sales periods once registered; skipping a $0 return still generates penalties in most states. Software or your compliance calendar should carry every assigned date.
Do service businesses need seller's permits?
Depends on the state and the service. Most states tax tangible goods and a defined list of services (repair, lodging, digital goods increasingly). Pure professional services usually stay exempt, but mixed transactions (a designer selling printed materials) often cross the line. Check your state's taxable-services list before assuming exemption.
Selling taxable goods? Register before the first sale.
Entity, EIN, and the state registrations lined up in the right order, with compliance monitoring tracking every filing frequency the states assign you.
This guide is written from the official sources below. Fees, forms, and deadlines change; confirm the current requirement with the agency before you file.
Disclosure. File.Business is a private filing service, not a government agency and not a law firm. We prepare and submit filings at your direction, and nothing on this page is legal or tax advice. Filing fees, deadlines, and statutory references are current as of the last-updated date shown above and can change. Confirm current requirements with the relevant state agency before you file.
