Sales tax basics founders get wrong

Sales tax is a tax your customer pays on certain purchases, which you collect at checkout and then send to the state. The money is never yours. You are acting as a collector for the government, holding the tax briefly before passing it on. That framing matters, because the most expensive sales tax mistakes come from treating it like revenue or ignoring it entirely.

This is general education, not tax advice. Sales tax rules vary by state and product, and the details change. The goal here is to help you understand the shape of the problem so you can ask the right questions and know when to bring in a specialist.

Most founders get one thing wrong: they assume sales tax only applies where their office is. The real question is where you have created an obligation to collect, and that can be in states you have never set foot in.

Nexus: where you actually owe

Nexus is the connection between your business and a state that requires you to collect that state's sales tax. There are two common kinds. Physical nexus comes from having something tangible in a state: an office, an employee, inventory in a warehouse. Economic nexus comes from selling enough into a state even with no physical presence there.

Economic nexus is the one that catches people. Since a 2018 Supreme Court decision, states can require you to collect sales tax once your sales into that state cross a threshold. A common threshold is $100,000 in sales or 200 transactions in a year, though it varies by state. Cross it, and you are expected to register and collect, regardless of where you are based.

• An office, store, or employees in a state create physical nexus
• Inventory stored in a state, including in a fulfillment warehouse, can create nexus
• Hitting a state's sales or transaction threshold creates economic nexus
• Each state sets its own thresholds and its own list of what is taxable

Register, collect, remit

Once you have nexus in a state, the process has three steps. First you register with that state's tax authority for a sales tax permit. Collecting before you register is generally not allowed, so registration comes first. Then you collect the correct tax on each sale, which depends on the customer's location and what you sold. Finally you remit, meaning you file a return and send the state the money you collected, usually monthly, quarterly, or annually depending on your volume.

What is taxable is not obvious. Many physical goods are taxable, but software, professional services, and digital products are treated differently from state to state. A subscription that is taxable in one state may be exempt in another. This is why a tool that calculates the right rate at checkout earns its keep once you sell across state lines.

The mistake that gets expensive

The common pattern looks like this. A company grows, sells nationwide, and never thinks about sales tax because nobody flagged it. Two years later they realize they crossed economic nexus thresholds in eight states and should have been collecting all along. Now they owe the back tax, plus penalties and interest, and they cannot go back and collect it from customers who have moved on.

Say you should have collected 7 percent on $500,000 of sales into a state. That is $35,000 you never charged your customers, and now the state wants it from you, with penalties on top. Multiply across several states and a problem you could have avoided becomes a number that affects whether the business is fundable or even solvent.

The fix is to look early. Map where your customers are, track your sales by state, and check your numbers against each state's thresholds at least once a year. Catching nexus the quarter you cross it is a registration form. Catching it two years late is a cleanup project.

When to bring in a specialist

Sales tax is a specialty, and a good advisor pays for themselves by keeping you out of the expensive scenario above. Bring one in when you start selling into multiple states, when you sell software or digital products where taxability is murky, or when you suspect you may already be behind. Many states offer voluntary disclosure programs that reduce penalties for companies that come forward before being audited, which is far better than waiting to be found.

You do not need to become a sales tax expert. You do need to know it exists, watch your sales by state, and ask for help before a quiet obligation grows into a loud one.