Sales tax nexus explained.

You started selling online because it felt simple. List a product, ship it, get paid. Then one afternoon you're reading a forum thread about "economic nexus" and "marketplace facilitator laws," and the ground feels like it just moved under your feet. Sales tax nexus is one of the most searched and least understood topics in ecommerce. This guide walks through what nexus means, how the two main types differ, how thresholds generally work, and where marketplace laws fit in — without pretending to be your tax advisor.

What "nexus" actually means

The word nexus is Latin for "connection." In sales tax, it describes the link between your business and a state that gives that state the right to require you to collect and remit sales tax. Without nexus, a state generally cannot compel you to collect on its behalf. With nexus, it typically can.

For decades, nexus was mostly about physical presence. If you had a warehouse, an office, or employees in a state, you had nexus there. Then ecommerce arrived, and sellers started reaching customers in states where they had no physical footprint at all. States responded by expanding the concept. Today, nexus is usually sorted into two buckets — physical and economic — and the practical rules sit at the intersection of the two.

Why this matters for a working seller: nexus determines where you may need to register, where you may need to collect, and where you may need to file — even if your only connection to a state is a customer's shipping address. It also sits underneath the numbers in our what you actually keep breakdown, because sales tax collected is not your money to keep.

Physical nexus versus economic nexus

Physical nexus

Physical nexus is the older, more intuitive idea. If your business has a tangible presence in a state, that state generally considers you connected to it. Common examples include:

• An office, warehouse, or storage location
• An employee, contractor, or agent working in the state
• Inventory stored in the state — including inventory held in a third-party fulfillment center
• Certain in-person activities such as trade shows, pop-ups, or installations

The inventory point catches many sellers off guard. If you ship products to a fulfillment center in a state, that state may treat you as having physical nexus there — even if you never set foot in it. Many Amazon FBA sellers first discover nexus this way.

Economic nexus

Economic nexus is the newer concept. It says that if you do enough business in a state — measured by sales dollars, transaction count, or both — you can create nexus there even with no physical presence at all. The theory is that a meaningful volume of economic activity is itself a connection.

Economic nexus is where most online sellers first encounter the topic. It is also where the rules vary the most, because each state sets its own threshold, its own measurement period, and its own rules about what counts.

How state thresholds generally work

Most states with economic nexus use a threshold test. A typical structure is a dollar amount of annual sales, a number of transactions, or both. Some states use an "or" test — either figure can trigger nexus. Others use an "and" test — both must be crossed. A few have dropped the transaction count entirely and rely on the dollar figure alone.

Because these rules differ from state to state and change over time, this guide intentionally does not provide a state-by-state table. A table like that would be out of date quickly and could easily be read as advice. The practical move is to know that thresholds exist, understand the two shapes they take, and confirm your specific numbers with each state's department of revenue directly.

One further layer worth knowing: measurement periods vary. Some states measure on a calendar year, some on a rolling twelve months, and some on a rolling four quarters. This matters because the same sales activity can cross a threshold on one state's clock and not on another's. Comparing "last year's total" against one state's threshold without matching its measurement window produces the wrong answer.

Marketplace facilitator laws — the part most sellers miss

Marketplace facilitator laws are the reason Amazon, Etsy, Walmart, and similar platforms now collect sales tax on many marketplace sales automatically. In most states that have adopted these laws, the marketplace — not the individual seller — is treated as the party responsible for collecting and remitting tax on sales made through its platform.

For sellers, this is genuinely helpful. It removes a large administrative burden for the transactions it covers. But it does not erase nexus, and it does not always eliminate every seller obligation. Three things sellers often miss:

• Registration and reporting may still apply. Some states require sellers to register, file zero returns, or maintain records even when the marketplace handles collection.
• Direct sales are not covered. If you also sell through your own website, wholesale, or a channel that is not a registered marketplace facilitator, those sales are generally your responsibility to assess and collect.
• Marketplace facilitator treatment varies. Not every platform is treated as a facilitator in every state, and not every product category is covered. The rules are state-specific.

This is why a seller can have nexus in a state and still have nothing to collect on marketplace sales there — while simultaneously having a collection obligation on direct sales in the same state. The two channels are assessed separately. Our platform fee comparison covers how the major marketplaces handle their side of this, which is a useful companion read for any seller running more than one channel.

When sellers typically look more closely at registration

There is no universal rule, but there are signals that commonly prompt sellers to examine registration requirements more carefully:

• You have physical nexus in a state — office, employee, inventory, or a long-term contractor.
• Your sales into a state have grown and you're unsure whether you've crossed its threshold.
• You sell through your own website or another non-marketplace channel into states where you have nexus.
• You've received a notice from a state's department of revenue.
• You're preparing to scale a channel and want to understand your footprint before volume increases.

Registration is state-specific, and so is the filing cadence that follows. Many sellers find it helpful to map their nexus footprint once a year, the same way they review their platform fees and pricing. It is a maintenance task, not a one-time event.

Common challenges

Several challenges come up repeatedly for online sellers confronting sales tax nexus. What follows is a general description of each — not prescriptions.

Confusing nexus with taxability

Nexus and taxability are two different questions. Nexus asks "can this state require me to collect?" Taxability asks "is this product or service taxable in this state?" A seller can have nexus in a state and sell only products that are not taxable there. Both questions have to be answered, and they have different sources.

Assuming the marketplace handles everything

Marketplace facilitator laws are broad, but they are not universal. Sellers with direct channels, wholesale relationships, or platforms that are not registered as facilitators in a given state often have obligations that marketplace collection does not cover. It is a common source of surprise during an audit or a state inquiry.

Letting thresholds creep

Nexus is not always obvious when it arrives. A state can be crossed quietly in the middle of a busy quarter, and the seller may not notice until much later. Periodic tracking is the common defense — pulling state-level sales figures and comparing them against each state's current threshold on a regular cadence.

Mixing up measurement periods

Two states can have similar dollar thresholds but very different measurement windows. A seller comparing last year's total against one state's threshold may be comparing the wrong number entirely. Matching the seller's reporting period to the state's measurement period is part of getting the answer right.

Waiting for a notice

States do not always send a letter before back taxes are owed. Many sellers only discover a gap after a review, a marketplace request, or a notice arrives. Getting ahead of it — mapping the footprint before a problem appears — is the theme here, not reacting to it.

Assuming small volume means no obligation

Small sellers sometimes assume that low volume means nexus does not apply to them. In reality, physical nexus can apply from day one regardless of volume — a single inventory location in a state can create nexus even for a seller with modest sales. Economic thresholds matter for sellers without physical presence; physical nexus does not wait for a threshold to be crossed.

An illustrative scenario

The following example is illustrative — it demonstrates how a seller might approach a nexus review, not what outcome to expect. It is not advice, and the details are hypothetical.

What to verify directly

Several aspects of sales tax nexus involve rules set by individual states and, in some cases, federal or marketplace policies. Sellers typically verify the following directly with the relevant party:

• Each state's current threshold — dollar amount, transaction count, or both, and whether the test is "and" or "or"
• Each state's measurement period — calendar year, rolling twelve months, or rolling four quarters
• Registration requirements in each state — including whether registration is required even when the marketplace collects
• Filing cadence — monthly, quarterly, or annual, which varies by state and often by volume
• Taxability of specific products or categories — some products are exempt, some are reduced-rate, and the treatment varies
• Marketplace facilitator rules per platform — which platforms are treated as facilitators in which states
• Voluntary disclosure programs — some states offer reduced exposure for sellers who come into compliance proactively

Because these rules change and vary by state, verification should be done at the time of decision rather than assumed from general knowledge or older summaries.

Beyond the US — the same idea, different words

If you sell into Canada, the European Union, Australia, or the UK, the underlying concept applies — when does a foreign seller become obligated to collect local consumption tax? — but the terminology and rules are different. None of these markets use the word "nexus."

Each framework has its own threshold structure, registration process, filing cadence, and rules about when marketplaces collect on the seller's behalf. The concepts parallel the US model in shape, but the specific rules — and the terminology — differ enough that a US-focused guide cannot substitute for market-specific reading.

If you sell into multiple Tier 1 markets, the practical approach is to treat each market separately. The US question ("do I have nexus in this state?") has a Canadian analogue ("am I over the small supplier threshold for GST/HST?"), an EU analogue ("do I need to register for VAT, and does OSS apply?"), and an Australian analogue ("have I crossed the ATO's GST turnover threshold?"). All four questions are answered by pulling sales data by market and comparing it against the current published thresholds.

Guides for the Canadian, EU, Australian, and UK frameworks are planned. In the meantime, each market's tax authority publishes its own registration and threshold guidance, and sellers with cross-border activity typically bring the specific figures to a qualified professional.

The general principle

Sales tax nexus is a moving map. It changes as your sales activity changes, as your operational footprint changes, and as states update their rules. Sellers who stay oriented to it — reviewing state-level sales figures, checking thresholds on a regular cadence, and bringing questions to a professional when the rules are unclear for their situation — tend to avoid the surprises that catch others during an audit or a state inquiry.

None of this is dramatic work. It is pulling reports, comparing numbers against published thresholds, and maintaining a list of states where the business has a connection. But the pattern across sellers who handle it well is consistently the same: they map the territory before they need the map, not after.