You shipped your first order to Wyoming on a Tuesday and forgot about it. Six months later, you discover that single sale was the start of a tax obligation in a state you've never visited, run by a department of revenue you can't pick out of a lineup, with penalties accruing the entire time. Welcome to the post-Wayfair world.
Since the U.S. Supreme Court decided South Dakota v. Wayfair, Inc. in June 2018, every state with a sales tax has built its own version of "economic nexus" — the idea that you owe sales tax in a state because of how much you sell there, not because you have an office, warehouse, or employee inside its borders. For online sellers, software-as-a-service vendors, and even traditional businesses that occasionally ship out of state, the rules are no longer a side issue. They are a recurring compliance project.
This guide walks through what economic nexus actually means in 2026, which thresholds to watch, how marketplace facilitator laws change your math, and what to do when you discover you should have registered months or years ago.
What Economic Nexus Means in Plain English
Before Wayfair, a state could only force you to collect its sales tax if you had a physical presence there: an office, a warehouse, inventory, employees, or sometimes even a single trade show booth. That bright-line "physical presence" test was famously set by Quill Corp. v. North Dakota in 1992.
The internet broke the model. South Dakota, frustrated at watching tax revenue leak out the door to remote sellers, passed a law in 2016 that required out-of-state retailers to collect its 4.5% sales tax once they exceeded $100,000 in sales or 200 transactions delivered into the state. Wayfair, Overstock, and Newegg challenged it. The Supreme Court sided with South Dakota, killing the physical-presence rule and opening the door for every other state to follow.
Within two years, all 45 states with a state sales tax (plus the District of Columbia, Puerto Rico, and over a dozen home-rule cities and parishes) had passed their own economic nexus laws. Each one picked its own thresholds, its own measurement period, and its own definition of which sales count.
The result: a seller doing roughly $2 million a year across 50 states can easily be on the hook to register, collect, file, and remit in 20 or 30 jurisdictions — most of which they will never set foot in.
The Common $100,000 Threshold (and the States That Are Different)
The single most common threshold is $100,000 in sales delivered into the state during the current or preceding calendar year. It's the South Dakota number that the Supreme Court blessed, and most states copied it word for word.
But the simple "$100,000 rule" hides three important variables: what counts as "sales," what counts as the lookback period, and whether there is also a transaction-count test.
Sales-Volume Variations
States diverge on which dollars count toward the threshold:
- Gross sales — every dollar of revenue from buyers in the state, including non-taxable items, services, exempt sales, and even resale transactions. This is the most aggressive measurement and the most common.
- Retail sales — gross sales minus wholesale and resale transactions. Common in states that try to focus the rule on consumer-facing sellers.
- Taxable sales — only the dollars that would actually be subject to sales tax. The narrowest definition, and friendly to sellers of mostly exempt goods (groceries, prescription drugs, certain SaaS).
If you sell to a mix of consumers and wholesalers, the same revenue can put you over the threshold in State A on a gross basis but well under in State B on a taxable basis. There is no shortcut: you have to read each state's rule.
High-Threshold States
A handful of states deliberately set higher bars:
- California, New York, and Texas: $500,000. These are the three states most likely to catch a small seller off guard purely because of population — a $500,000 threshold is easier to hit than it sounds when you're shipping to the country's three largest economies.
- Tennessee, Alabama, Mississippi: $250,000 (varies by state and rule). Mississippi historically used $250,000; other states have moved up and down over time.
New York also keeps a quirky dual test: you must exceed $500,000 AND 100 transactions during the prior four sales tax quarters. Both prongs have to be met.
The 200-Transaction Trap (and Its Slow Death)
In the original South Dakota statute, the threshold was "$100,000 OR 200 transactions." That "or" matters: a seller doing 250 small orders averaging $30 each — only $7,500 of revenue — would still trip nexus.
Plenty of states copied the transaction count. It was a disaster for small Etsy sellers, eBay shops, and digital download businesses. A craft seller with $40,000 in annual revenue could end up registered in a dozen states with negative profit on the compliance work itself.
The trend in 2025 and 2026 is unambiguous: states are killing the transaction count. By January 2026, at least 16 states had eliminated their transaction thresholds, including Illinois (effective January 1, 2026), Indiana, Louisiana, North Carolina, South Dakota itself, and Wyoming. Most of them now use a clean revenue-only threshold.
But "most" is not "all." Connecticut still uses $100,000 AND 200 transactions (both required). New York still uses $500,000 AND 100 transactions. A few states still use the original "or" formulation. You cannot assume the transaction count is gone — check each state where you sell.
Lookback Period Variations
Even when the dollar amount is the same, states measure it over different windows:
- Previous calendar year only — common, and easier to track.
- Current calendar year only — a moving target; you can trip nexus mid-year.
- Either the current OR the preceding calendar year — once you trip, you stay tripped for at least the next year.
- Trailing 12 months — a rolling window, the hardest to track manually.
- Quarterly — used by a few states for the registration trigger.
If you sell into a state seasonally — say, a holiday-heavy gift business — a calendar-year measurement protects you if your spike is across two years (Nov-Dec to Jan), while a rolling 12-month measurement does not.
Marketplace Facilitator Laws Change the Math
Right after Wayfair, states realized they had an easier collection target than chasing tens of thousands of small remote sellers individually: the marketplaces themselves. By 2026, every state with a sales tax has a marketplace facilitator law requiring platforms like Amazon, eBay, Etsy, Walmart Marketplace, Shopify (in some configurations), Airbnb, and Uber Eats to collect and remit sales tax on behalf of their third-party sellers.
For sellers, this is mostly good news — and partially a trap.
The good news: If you sell exclusively through a marketplace that collects on your behalf, the marketplace handles the tax. You generally do not need to register in every state where your buyers live, because the marketplace already has.
The trap: Most states still count your marketplace sales toward your own economic nexus thresholds. Here's the scenario that catches sellers:
- You sell $250,000 a year on Amazon, which collects sales tax for you in all 45 states.
- You also run a Shopify store that does $80,000 a year.
- State X has a $100,000 threshold measured on gross sales including marketplace sales.
- Your Amazon sales into State X are $90,000. Your Shopify sales into State X are $15,000. Total: $105,000.
- You have economic nexus in State X — and your Shopify sales are NOT covered by Amazon's collection. You owe registration, collection, and filing for the $15,000 channel.
This is the rule in most states. A handful of states (the count keeps changing) exclude marketplace sales when measuring your direct-channel nexus, but you cannot assume that. Treat marketplace sales as counting unless the state explicitly says otherwise.
The same principle applies in reverse: if you have direct-channel nexus in a state, your marketplace can still collect on the marketplace orders, but you also have to file a return reporting your own direct sales, even if the tax collected by the marketplace is recorded somewhere on the return as a deduction. You don't escape filing; you just escape collecting.
What to Actually Do: A Practical Compliance Routine
Here is a workable monthly and quarterly process for a growing online business.
1. Pull a Sales-by-State Report Every Month
Whatever platform you use — Shopify, WooCommerce, BigCommerce, Stripe, your accounting system — you need a recurring report that shows gross sales by state (and ideally taxable vs. exempt) for the trailing 12 months. If you sell on multiple channels, you need the consolidated number.
This is the single most important habit. Without it, you are guessing.
2. Compare Against a State Threshold Chart
Maintain a simple spreadsheet or use a tax compliance tool (Avalara, TaxJar, Numeral, Anrok for SaaS, etc.) that lists each state's threshold, lookback period, and whether transaction counts apply. The official state-by-state guide from the Sales Tax Institute is widely used and updated as states change rules.
Flag any state where your trailing-12-month sales are above 75% of the threshold. That's your warning list — the states where you're a few months away from registration.
3. Register Promptly When You Cross
When you trip a threshold, most states require registration "by the next transaction" or "by the first day of the following month." A few give you a 30- or 60-day grace period. Almost none give you longer than that.
The registration itself is usually free or cheap (under $100). The painful part is the ongoing filing — even if you have zero sales in a quiet month, you typically still have to file a zero return. Missing zero returns is a leading cause of late-filing penalties.
4. Track Your Filing Frequency
Each state assigns you a filing frequency (monthly, quarterly, or annually) based on your expected tax liability. Higher-volume states will start you on monthly filing; smaller states often default to quarterly or annual. Watch your mail and your state portal — frequency assignments change as your sales grow, and missing the change date causes problems.
5. Reconcile Sales Tax Collected Against Sales Tax Owed Every Month
Sales tax collected is not your money. It is a liability you hold in trust for the state. Sloppy bookkeeping that mixes collected sales tax with revenue is the single fastest way to dig yourself into a hole — you spend the money, then discover at filing time you owe it back.
The cleanest approach: book sales tax collected to a separate liability account (something like Liabilities:Sales-Tax-Payable:CA), and reconcile that balance against your filed return amount every period. If the numbers don't match, you have a bug somewhere — usually a non-taxable item misclassified as taxable, or a tax-rate change you missed.
What If You Should Have Registered Months Ago?
Many sellers discover, mid-audit or while reading something like this article, that they have been over the threshold in three or seven or twelve states for a year or more. The panic move is to file forward and hope nobody notices. The smart move is a Voluntary Disclosure Agreement (VDA).
A VDA is a formal program offered by virtually every state where you raise your hand, admit you were not registered, agree to register going forward, and pay the back taxes you should have collected — usually with a capped lookback period (often three or four years instead of unlimited) and with most penalties waived. Interest still applies.
The critical timing rule: you must approach the state first. If the state contacts you with an audit notice or even an informal inquiry first, you are no longer eligible for the VDA program. That single rule is why proactive sellers come out far better than reactive ones.
If you owe taxes in multiple states, the Multistate Tax Commission (MTC) runs a coordinated VDA program that lets you apply once and negotiate with many states under similar terms. Your identity is kept anonymous to each state until you have agreed to register, which protects you during negotiation.
The catch with a VDA is that you usually have to pay the back taxes out of pocket — you can't go back and collect tax from customers from two years ago. That's why VDAs hurt more the longer you wait. The math gets worse every month.
The State-Level Edge Cases to Know
A few specific traps come up enough to flag:
- Home-rule states (Alabama, Colorado, Louisiana, Alaska). Some cities and counties run their own sales tax separately from the state. You can be registered with the state and still be out of compliance in a city. Colorado has been simplifying this through its SUTS system but it's still a minefield.
- Alaska has no statewide sales tax but several local jurisdictions do, and they banded together as the Alaska Remote Seller Sales Tax Commission. Different thresholds, different filings.
- Streamlined Sales Tax (SST) member states — about half the states — share a simplified registration and a free certified service provider option that can reduce your compliance cost dramatically for small sellers. Worth checking if your states are members.
- Digital goods, SaaS, and services. What counts as "tangible personal property" in one state may be exempt in another. SaaS is taxable in roughly 20 states, exempt in the rest. Digital downloads (books, music, software) follow yet another patchwork. If you sell anything other than physical goods, taxability research is its own project.
- Trailing nexus. Even if you drop below a state's threshold, many states require you to keep filing for a "trailing" period — often the remainder of the current year plus the full following year — before you can deregister.
Keep Your Multistate Records Clean from Day One
Sales tax compliance lives or dies on the quality of your underlying books. If you can produce a clean, by-state, by-channel revenue report on demand, the work is annoying but manageable. If your books are a tangle of merged platforms, miscategorized refunds, and inconsistent product codes, every state filing becomes archaeology.
Beancount.io gives you plain-text, version-controlled accounting where every transaction is auditable and every state's tax liability can be tagged, queried, and reconciled with a simple report. Because the data is in human-readable text — not a proprietary database — you can build the by-state, by-channel reports you need without waiting on someone else's roadmap. Get started for free and keep your multistate compliance work on solid ground from the first sale.