Selling Across State Lines? The Tax Obligation You May Have Already Triggered

For decades, the rules of sales tax were refreshingly simple for small businesses. If you had a physical presence in a state — a store, a warehouse, an office — you collected that state's sales tax. If you didn't, you generally didn't. A boutique in Ohio could ship a dress to a customer in Arizona without giving Arizona's tax authorities a second thought.

That era ended in June 2018, when the Supreme Court decided South Dakota v. Wayfair. The ruling dismantled the physical-presence standard and replaced it with something broader and far less visible: economic nexus. Under the new framework, simply reaching a certain volume of sales or transactions into a state can create a tax collection obligation — even if you've never set foot there.

For small and mid-size businesses, especially those selling online, this is one of the most commonly misunderstood compliance risks in the tax code today.

What Economic Nexus Actually Means

Economic nexus is a threshold-based standard. Each state sets its own rules, but the most common benchmark — modeled on South Dakota's original law — is $100,000 in gross revenue or 200 separate transactions delivered into the state over a calendar year.

Cross that line, and the state generally considers you to have nexus: a sufficient connection to require you to register, collect, and remit sales tax on sales to customers there. Importantly, most states count revenue from all your sales into the state, not just taxable ones, and many include marketplace-facilitated sales in the calculation even when a platform like Amazon or Etsy handles collection on your behalf.

The thresholds vary. Some states set the bar higher. A handful impose only a transaction count. Others exclude marketplace sales entirely. The point is that there is no single national rule — there are dozens of them, and they don't stand still.

A Scenario That Plays Out More Often Than You'd Think

Consider a hypothetical but entirely realistic example. A specialty food company based in Colorado builds a loyal online following. Through a mix of its own website and a growing wholesale relationship, it ships roughly $85,000 of product annually to customers in Texas — comfortably under that state's threshold, so no obligation there. But it also ships $120,000 to customers in New York and processes more than 300 individual New York orders.

Neither the owner nor the bookkeeper notices. Sales tax is collected only in Colorado. Then the company applies for a loan, and the lender's due diligence surfaces the gap. A voluntary disclosure agreement gets negotiated, back taxes are calculated, penalties are partially waived — but the episode still costs thousands of dollars and months of administrative distraction, all for obligations that could have been managed prospectively at a fraction of the cost.

The uncomfortable truth is that many businesses discover nexus the way this one did: accidentally, and after the fact.

Why This Catches Growing Businesses Off Guard

Three patterns show up repeatedly.

Growth itself creates the problem. A business that was safely under every state's threshold last year may blow through several of them this year. Success, quite literally, generates new compliance obligations.

Marketplaces create false confidence. Many owners assume that because Amazon, Walmart, or eBay collects sales tax on marketplace transactions, they're covered. Sometimes they are. Often they aren't — particularly for sales made through their own website to the same states.

Service businesses assume they're exempt. While sales tax traditionally applies to tangible goods, a growing number of states now tax digital products, SaaS subscriptions, and certain professional services. A consulting firm selling online training subscriptions may have nexus obligations it has never considered.

A Practical Checklist: Where Might You Already Owe?

If you sell beyond your home state, work through these steps:

1. Pull your sales data by state. Using shipping addresses, total your gross revenue and transaction counts for each destination state for the current and prior calendar years.

2. Compare against each state's thresholds. Roughly forty states plus several local jurisdictions impose economic nexus rules. The Tax Foundation and each state's department of revenue publish current thresholds.

3. Account for marketplace sales. Determine whether each state includes or excludes marketplace-facilitated sales when measuring your totals.

4. Review your product and service taxability. Confirm what you sell is actually taxable in each destination state — and check whether digital offerings have changed the picture.

5. Look for physical nexus, too. Inventory stored in a fulfillment center, a remote employee, or a trade show where you take orders can create nexus independent of the economic thresholds.

6. Consider voluntary disclosure. If you find historical exposure, most states offer programs that limit look-back periods and reduce penalties for businesses that come forward proactively — a far better outcome than waiting for an audit notice.

Turning a Compliance Headache Into a Manageable Routine

The businesses that handle multi-state sales tax well share a common trait: they treat it as a recurring process rather than a crisis. That means monitoring sales volumes against thresholds quarterly, registering promptly when a line is crossed, automating rate calculation where volume justifies it, and filing on schedule in each registered state.

Nexus rules are not going away, and they continue to evolve — several states have expanded them to cover more digital services in recent years. The businesses that stay ahead of these obligations protect themselves from penalties, keep their financial statements clean for lenders and buyers, and preserve the peace of mind that comes from knowing there are no surprises waiting in a filing drawer.

If your revenue map has changed in the last two years, now is the time to find out exactly where you stand. A structured nexus review is one of the highest-return compliance exercises a growing business can undertake — and considerably cheaper than the alternative.