US Sales Tax Economic Nexus: What Founders Actually Need to Track

Most states adopted some version of South Dakota's original safe harbor: $100,000 in sales, or 200 separate transactions, in the current or prior calendar year, whichever threshold you cross first triggers the obligation. That said, this isn't universal -- some states have removed the 200-transaction leg entirely and rely purely on the dollar threshold (Wyoming did this in 2024, for instance), some states use a higher dollar threshold like $250,000, and rules do shift over time as states adjust their statutes. Treat $100,000/200 transactions as the common baseline to be aware of, not a guaranteed figure for every state you sell into.

Economic nexus didn't replace physical presence nexus -- it added a second way to trigger the obligation. If your business has genuine physical presence in a state (an office, an employee, or notably, inventory stored in that state -- which matters directly for founders using Amazon FBA, since Amazon distributes inventory across its own fulfillment centers in multiple states), you can owe sales tax collection duties there regardless of your sales volume, purely from that physical presence. FBA sellers in particular sometimes don't realize their inventory sitting in an Amazon warehouse in a state creates nexus there independent of the economic thresholds discussed elsewhere on this page.

Founders focused on US federal tax obligations (Form 5472, income tax) sometimes don't realize state-level sales tax is a completely separate system with its own registration, collection, and filing requirements per state. It's entirely possible to be fully compliant on the federal side while quietly accumulating economic nexus obligations in several states without realizing it, especially if your sales are spread across many states in moderate amounts rather than concentrated in one place you'd naturally think to check.

States generally don't wait for you to self-report a missed nexus threshold -- if a state audit or notice determines you should have been collecting and weren't, you can be assessed for the uncollected tax retroactively, plus penalties and interest, and in some cases this liability falls on the business itself rather than being passed to customers after the fact (since you didn't collect it from them at the time of sale). This is meaningfully more expensive than proactive compliance would have been, which is the core argument for tracking exposure before it becomes a problem rather than waiting to see if a state ever notices.

Once you determine you have nexus in a state, you generally need to register with that state's tax authority, begin collecting the appropriate sales tax rate on sales into that state (rates and even what's taxable vary significantly by state and sometimes by locality within a state), and file periodic sales tax returns (monthly, quarterly, or annually depending on your volume and the state's rules). This is genuinely one of the more operationally complex parts of running a US-facing e-commerce business as a non-resident, and many founders use a dedicated sales tax compliance service or software specifically because manually tracking dozens of states' differing rates and filing calendars isn't realistic to do by hand at any meaningful sales volume.

The practical challenge is that nexus is triggered automatically the moment you cross a state's threshold -- there's no notification from the state telling you it happened. Founders selling across many states typically need either a dedicated nexus-tracking tool that connects to their sales platform (Shopify, WooCommerce, etc.) and monitors progress toward each state's threshold, or a disciplined manual process of reviewing state-by-state sales data periodically. Waiting until a state sends a notice (which usually means a penalty is already accruing) is the expensive way to find out you'd crossed a threshold months earlier.

Before 2018, a state generally couldn't require a business to collect its sales tax unless that business had a physical presence there -- an office, a warehouse, an employee. The Supreme Court's decision in South Dakota v. Wayfair overturned that rule, allowing states to establish 'economic nexus': the obligation to collect and remit sales tax based purely on your sales volume into that state, regardless of physical presence. For a non-resident founder running an e-commerce or digital-goods LLC with customers scattered across the US, this is directly relevant -- you can owe sales tax collection duties in a state you've never set foot in, purely because of how much you sold there.

If you sell primarily through a marketplace like Amazon, Etsy, or eBay rather than your own website, many states now have 'marketplace facilitator' laws that shift the sales tax collection duty onto the marketplace itself rather than you as the individual seller. This doesn't eliminate your need to understand nexus (some of your own sales may still count toward thresholds even if the marketplace handles collection on marketplace sales specifically), but it does meaningfully reduce the collection burden for marketplace-heavy sellers compared to those selling primarily direct-to-consumer through their own Shopify or similar storefront.