US · Journal
Sales Tax Nexus: What US E-commerce Founders Get Wrong
US sales tax nexus explained for e-commerce founders — economic vs physical nexus after Wayfair, marketplace facilitator rules and the mistakes that cost most.
US sales tax nexus explained for e-commerce founders — economic vs physical nexus after Wayfair, marketplace facilitator rules and the mistakes that cost most.
Sales tax nexus is the connection between your business and a US state that obliges you to register, collect and remit that state's sales tax — and since the Supreme Court's 2018 Wayfair decision, you can create it purely through sales volume into a state, with no office, warehouse or person there at all. The mistakes that cost e-commerce founders the most are assuming nexus needs a physical presence, assuming a marketplace handles everything, and waiting until a state sends a notice before registering. This guide explains the principles so you can find your real obligations before they find you — without relying on specific thresholds that vary by state and change.
The United States has no national sales tax. Instead, most states (and many local jurisdictions within them) levy their own sales tax, each with its own rules, rates, registration process and filing schedule. A business only has to collect a given state's sales tax if it has nexus there — a sufficient connection to justify that state imposing its rules on you.
For decades, nexus essentially meant physical presence. If you had no people, property or inventory in a state, that state generally could not require you to collect. That single assumption is now out of date — and it is the root of most founder errors.
There are two ways to create nexus today, and you can trigger either one:
Understanding both is non-negotiable for any e-commerce business selling across state lines.
Physical nexus is created by a tangible link to a state. The common triggers for an online seller include:
The inventory point catches a large number of sellers by surprise. Using a national fulfilment network can place your stock in numerous states simultaneously, each potentially creating a registration and collection obligation regardless of where your company is based. Founders who use third-party logistics should specifically ask where their inventory is held, because that map often defines their physical-nexus footprint.
In South Dakota v. Wayfair, Inc. (2018), the U.S. Supreme Court overturned the long-standing rule that a seller needed physical presence to be required to collect sales tax. The Court held that a state could require collection based on the seller's economic activity in the state — its volume of sales or number of transactions — even with no physical presence at all. The decision itself is published by the Supreme Court of the United States.
In the wake of Wayfair, essentially every state with a sales tax adopted an economic nexus standard. The principle is the same everywhere: cross a defined level of sales into the state — measured by revenue, by transaction count, or by either — and you create nexus and must register, collect and remit.
The crucial caution: the specific thresholds, the measurement period, and whether transaction count even counts vary from state to state, and states change them. Some have moved away from transaction-count tests; some measure gross sales while others measure taxable or retail sales; the look-back window differs. For that reason this article does not quote specific numbers — any figure should be checked against each state's current published rules at the time you assess, because relying on an out-of-date threshold is itself a common and expensive mistake.
Most states have also enacted marketplace facilitator laws. These shift the duty to collect and remit sales tax on marketplace sales onto the marketplace itself, rather than the individual seller. If you sell through a large marketplace, the marketplace generally collects and remits the tax on those transactions for you.
This is genuinely helpful — but it is where a second big mistake lives. Marketplace facilitator relief is not a blanket exemption:
The safe mental model: a marketplace handling its own collection does not mean your business has no sales tax footprint. It means part of your footprint is covered, and the rest is still yours.
Once you have nexus in a state, a sequence of obligations follows, and each step has its own pitfalls.
The administrative load scales quickly with the number of states, which is why many growing sellers move to automated tax software and professional oversight rather than tracking dozens of state portals by hand. The IRS provides general small business and self-employed tax guidance, though sales tax itself is administered at the state level by each state's department of revenue.
Nearly every avoidable sales tax problem traces back to a handful of misconceptions:
The through-line is that nexus is dynamic. A footprint that was clean last year can trigger obligations in several new states after a strong sales quarter or a change in fulfilment, so it needs periodic review rather than a single setup pass.
For an e-commerce founder, a workable routine looks like this:
We never state a current state threshold or rate we cannot verify against that state's official guidance; where a number varies or has changed, we confirm it before relying on it. You can model the impact of expanding into new states with our calculators as a first step.
Next Tax Source works with US, UK and UAE businesses, and our US state and sales tax team handles nexus analysis, registrations and multi-state filings for e-commerce sellers. We map where you have physical and economic nexus, separate your marketplace and direct obligations, and keep the position under review as you grow into new states.
A US-licensed professional — a CPA or Enrolled Agent — reviews and signs off the position before anything is filed. Agents and software prepare the workpapers; a qualified human approves them, and we confirm every state threshold and rate against current official guidance rather than assuming.
If you sell across state lines and are not certain where you have obligations, an early review is far cheaper than a multi-state catch-up after a state notice. Book a consultation and we will assess your nexus footprint and tell you plainly where you need to register, what is already covered, and what needs confirming. Our pricing is published up front.
Nexus is the connection between your business and a US state that obliges you to register for, collect and remit that state's sales tax. There is no national US sales tax — each state sets its own rules. You can create nexus through physical presence (an office, employees, or inventory stored in the state) or, since the 2018 Wayfair decision, through economic activity alone, meaning enough sales into the state even with no physical footprint there.
Possibly yes. After the Supreme Court's 2018 Wayfair decision, states can require collection based on economic nexus — your volume of sales or transactions into the state — with no physical presence required. Almost every state with a sales tax adopted an economic-nexus standard. The specific thresholds and how they are measured vary by state and change over time, so you should check each state's current published rules rather than rely on a remembered figure.
Only for sales made through that marketplace. Marketplace facilitator laws shift collection and remittance for marketplace transactions onto the marketplace, which is genuinely helpful — but it is not a blanket exemption. Sales through your own website or other direct channels remain your responsibility, marketplace sales may still count toward your economic-nexus measurement in some states, and registration can still be required. Mixed-channel sellers must assess their direct-sales obligations themselves.
Liability generally accrues from when nexus was created, not from when the state notices you, so waiting usually means owing back tax plus interest and penalties — and the cost of catching up grows the longer you leave it. Collecting tax without being registered, or missing required filings (including zero returns when no tax is due), also draws penalties. It is far cheaper to identify obligations and register proactively than to remediate after a notice.
Not as fixed figures in an article. The thresholds, the measurement period, whether transaction count is included, and which sales are measured all vary by state and change over time. We never publish a current state figure we cannot verify against that state's official guidance. Book a consultation and a US-licensed professional (CPA or Enrolled Agent) will check the current rules for the states that matter to you, then review and sign off any registrations and filings.