Sales Tax Nexus Explained: What Growing Businesses Need to Know Before They Expand

A business can owe sales tax in a state it has never set foot in. That single fact surprises more growing businesses than almost anything else in this guide, and it is usually discovered at the worst possible time: during a notice from a state tax authority rather than during planning.

The concept behind this is called nexus, and understanding it before you expand is far cheaper than untangling it after the fact.

What Nexus Actually Means

Nexus is the connection between a business and a state that is significant enough to create a tax obligation in that state. Historically, nexus meant physical presence: an office, a warehouse, an employee, or inventory stored in a state. If you had a physical footprint there, you owed sales tax there.

That is still true, but it is no longer the whole picture.

Economic Nexus: The Rule That Changed Everything

Following a 2018 Supreme Court decision, states gained the ability to require sales tax collection based purely on the volume of sales into that state, with no physical presence required at all. This is called economic nexus, and nearly every state with a sales tax now has one.

The specific thresholds vary by state, but the most common pattern is a combination of a dollar amount of sales and a transaction count within a twelve-month period, commonly built around figures like 100,000 dollars in sales or 200 separate transactions, whichever comes first. Some states use only a dollar threshold. A handful set the bar meaningfully lower or higher. Because these thresholds change and vary state by state, the specific number for any state you are selling into should always be confirmed directly rather than assumed.

Physical Nexus Still Matters

Even with economic nexus now in play, physical presence still creates an obligation on its own, and it can show up in less obvious ways than an office lease.

• An employee working remotely from a state where the business has no other presence
• Inventory stored in a third-party fulfilment warehouse, including many ecommerce fulfilment networks
• A contractor or salesperson regularly working within a state on the business’s behalf
• Attending trade shows or doing business in person within a state on a recurring basis

How to Know Where You Have Crossed a Threshold

This requires tracking sales by state, not just in total. A business selling nationally through an ecommerce platform can cross an economic nexus threshold in a new state every few months as it grows, and without deliberate tracking, that moment can pass unnoticed for a full year or more before anyone realises a filing obligation exists.

What to Do Once You Cross a Threshold

• Register with the state. You generally need to register for a sales tax permit before you begin collecting, not after.
• Start collecting sales tax on transactions in that state. Once registered, the correct rate needs to be applied at checkout or on invoices going forward.
• File on the state’s required schedule. Filing frequency, monthly, quarterly, or annually, is typically assigned based on your sales volume in that state.
• Remit what you collected. Sales tax collected from customers belongs to the state, not the business, and should be tracked as a liability rather than revenue from the moment it is collected.

Marketplace Facilitator Laws

If you sell through a marketplace such as Amazon, Etsy, or Walmart Marketplace, many states now require the marketplace itself to collect and remit sales tax on your behalf for sales made through that platform. This does not necessarily remove your own registration or filing obligation for sales made outside that marketplace, and the two systems need to be reconciled against each other rather than assumed to cancel out.

Common Mistakes

• Assuming nexus only applies if you have a physical office in a state
• Not tracking sales by state until a filing obligation has already been missed
• Registering in a state without updating checkout or invoicing systems to actually collect the tax
• Treating marketplace-collected tax and self-collected tax as the same thing without reconciling them
• Waiting for a notice from a state before addressing a known threshold crossing

The Bottom Line

Sales tax nexus is one of the more invisible risks a growing business carries, precisely because nothing forces you to notice it in the moment. The businesses that manage it well are the ones tracking sales by state as a routine part of monthly bookkeeping, not the ones scrambling to reconstruct a year of sales history after a state notice arrives.

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