What is economic nexus for e-commerce sellers?
Economic nexus means a state can require an out-of-state seller to register and collect sales tax based on selling activity into that state alone, with no physical presence — the position established by the 2018 South Dakota v. Wayfair decision. Each state sets its own threshold and they change, so what the seller needs is reliable tracking of sales by state; whether a registration obligation has been triggered is a determination for their CPA or tax adviser.
Since the 2018 South Dakota v. Wayfair Supreme Court decision, states can require out-of-state sellers to collect sales tax based on economic activity alone — no physical presence required. This is called "economic nexus," and it's one of the most common blind spots for growing e-commerce businesses.
How It Catches Businesses Off Guard
Each state sets its own threshold — commonly a certain dollar amount of sales or number of transactions within the state per year. Cross that threshold, and you may owe sales tax registration and collection obligations in that state, even if you've never set foot there and have no employees or warehouses located in it.
Because thresholds are state-specific and change over time, a business selling well across multiple states can accumulate nexus obligations in several states without anyone flagging it — until an audit or a compliance review surfaces it.
Why This Matters for Your Bookkeeping
Nexus tracking isn't a one-time setup — it needs to be monitored continuously as sales grow and shift across states and channels (your own storefront, Amazon, other marketplaces). Bookkeeping that tracks revenue by state, not just in aggregate, is what makes this visible in the first place.
Physical Nexus Did Not Go Away
Economic nexus was added to the rules; it did not replace the older one. Physical presence still creates an obligation, and for e-commerce sellers the most common form of it is not an office or an employee — it is inventory. Stock held in a third-party fulfilment warehouse can constitute physical presence in that state, and a fulfilment network may move your inventory between states without asking you.
That is the version of this problem that surprises people most, because the trigger is a logistics decision somebody else made. If you use a fulfilment network, knowing which states have held your stock is part of knowing your footprint.
The Marketplace Facilitator Confusion
Most states now require marketplaces to collect and remit sales tax on transactions made through them. That genuinely removes a large part of the collection burden for marketplace sellers — and it is the source of the most common misreading in this whole area.
Two things are easy to conflate. Whether the marketplace collects the tax is one question. Whether those sales still count toward the threshold that creates your own registration obligation is a separate question, and the answer varies by state. A seller who reads "the marketplace handles it" as "I have no obligation anywhere" can be registered-and-not-know-it in several states — particularly if they also sell through their own storefront, where nobody is collecting on their behalf.
The bookkeeping consequence is specific: marketplace and direct sales have to be distinguishable by state, not merged into one revenue figure. Merged, the question cannot be answered at all.
Obligations Start Before Anyone Notices Them
A threshold is crossed on a particular day, and the obligation attaches from a point defined by that state's rules — not from the day someone reviews the position. That gap is where liability accumulates, and it is why a periodic review is worth more than an annual one: the cost of finding out late is the uncollected tax plus whatever the state adds, on sales where you never charged the customer.
There is also a tail. In several states an obligation persists for a period after activity drops below the threshold, so falling out of a state is not automatically the end of it.
What Your Books Have to Produce
None of the above is answerable from a ledger that records total revenue. What makes the question answerable at all:
- Sales recorded by destination state, as they post rather than at year end.
- Marketplace sales separable from direct sales, per state.
- Transaction counts as well as dollar amounts, because some thresholds use both.
- Exemption and resale documentation attached to the transaction it belongs to.
- Where inventory has been held, if you use a fulfilment network.
That is bookkeeping, and it is the part we do. It turns "are we registered where we should be?" from an investigation into a report.
What to Do About It
- Track sales by state, not just total revenue
- Review your nexus footprint periodically as you grow, not just once
- Work with a sales tax filing service or tax advisor for actual registration and filing once nexus is triggered
This is general information, not tax advice for your specific situation — sales tax rules vary by state and change over time, so confirm your specific obligations with a qualified tax advisor.
How We Help
Our e-commerce accounting support includes tracking sales by state and channel, so this visibility exists in your books before it becomes a surprise.
Once your adviser has identified the states where you are registered and required to file, the returns themselves become recurring preparation work. Our sales tax return preparation covers assembling the period’s transaction data by state, reconciling the liability to your ledger and preparing the return for your review and filing. Which states you must register in stays a determination for your tax adviser.