State Sales Tax Nexus: When Your Business Must Collect Sales Tax

If you sell across state lines in the United States, you face a critical compliance question that can cost you thousands in back taxes and penalties if you get it wrong: in which states must you collect sales tax?

The answer hinges on a legal concept called state sales tax nexus—a sufficient connection to a state that triggers your obligation to collect and remit its sales tax. If you're just getting started with sales tax, our guide to sales tax for small businesses in the US covers the fundamentals. Here, we're diving into the nexus rules that determine where you owe it.

Before 2018, establishing nexus was straightforward: you needed a physical presence. The Supreme Court's South Dakota v. Wayfair decision changed everything, expanding sales tax obligations based purely on your economic activity within state borders.

This shift hit online sellers hard. If you operate an e-commerce business, hire remote employees, or use fulfillment centers in multiple states, you almost certainly have sales tax nexus in states where you've never set foot.

Let's walk through what nexus actually means, how to figure out where you owe sales tax, and what happens when you miss a threshold.

What Is Sales Tax Nexus?

Nexus is the legal term for a sufficient connection—economic or physical—that gives a state authority to require you to collect and remit its sales tax. Without nexus, a state can't compel you to act as its tax collector, no matter how much you sell there.

There are two main categories.

Physical Nexus

You have physical nexus when your business has a tangible presence in a state. This includes:

• An office, store, or warehouse
• Employees (including remote staff who work in the state)
• Inventory stored anywhere in the state—including at third-party fulfillment centers
• Company vehicles operating in the state
• Business equipment or property
• Temporary presence like trade shows or pop-up shops (though rules vary by state)
• Affiliate nexus: Related entities or independent reps acting on your behalf

If you use Amazon FBA, your inventory is scattered across a dozen or more states. You have physical nexus in most of them—and likely didn't know it.

Economic Nexus

Since Wayfair, most states enacted economic nexus laws. These establish nexus based on sales volume or transaction count, regardless of physical presence. The Federation of Tax Administrators tracks state-by-state thresholds, which commonly are:

• $100,000 in annual sales to customers in the state, OR
• 200 transactions per year

But "common" doesn't mean universal. Some states use only dollar thresholds, others $250,000 or $500,000. Some measure on a rolling 12-month basis; others reset each calendar year. Some count only taxable sales; some count everything. Check the FTA tracker or your state's department of revenue website for specifics.

How to Figure Out Your Nexus Exposure

Step 1: Map Your Physical Presence

List every state where you have:

• A physical location (yes, even a home office where a remote employee works)
• Inventory stored or in transit
• Employees or contractors
• Any other physical foothold

You have physical nexus in each of these states and must collect their sales tax (if the state has one and your products or services are taxable).

Step 2: Track Sales by State

Your accounting software should track customer locations and report sales by state. Review this data at least quarterly.

Compare your revenue and transaction count against each state's economic nexus thresholds. The goal is catching the threshold approach so you can register proactively.

Step 3: Stay Current on Changes

State nexus laws change. New thresholds get enacted. Court decisions shift the landscape. Set an annual reminder to review your nexus status after any major business change—new employee location, new fulfillment center, acquisition, or significant shift in sales channel.

When Nexus Is Triggered: What to Do

Once you establish nexus in a state, you move into execution mode.

Register for a Sales Tax Permit

You must register before collecting tax. Go to the state's department of revenue website. You'll need:

• Your business name and legal structure
• Federal EIN
• Estimated annual sales in the state
• Date you plan to start collecting

Determine What's Taxable

Not everything is taxable in every state. Software, services, digital goods, and clothing all vary by jurisdiction. You need to know whether your specific offerings are taxable, exempt, or reduced-rate in each state.

Configure Your Sales System

Set your point-of-sale or e-commerce platform to charge the correct rate based on customer location (destination-based) or your location (origin-based). Most platforms support this, but setup matters.

Collect From Day One

Start collecting from the effective date the state specifies. Don't collect retroactively unless explicitly instructed.

File and Remit on Schedule

File returns and remit collected tax according to the state's schedule (monthly, quarterly, or annual). The state usually specifies based on your expected volume.

Marketplace Facilitator Laws: A Small Reprieve

If you sell through Amazon, Etsy, eBay, or Walmart Marketplace, the marketplace may be responsible for collecting and remitting sales tax on your behalf. Most states have enacted marketplace facilitator laws that shift this burden to the platform. The IRS provides guidance on which sales channels fall under these laws.

But don't ignore these sales channels:

• Confirm which sales are covered by marketplace facilitator laws (some states carve out exceptions)
• Don't double-collect tax
• Still track marketplace sales when calculating whether you've hit economic nexus thresholds
• Collect tax yourself on direct sales through your own website where you have nexus

Common Nexus Pitfalls

Amazon FBA and Inventory Nexus

Using Fulfilled by Amazon creates physical nexus in nearly every state where Amazon has a fulfillment center. Many sellers don't realize this until audit. If you use FBA, you have nexus broadly.

Remote Employees

Hiring a remote employee in a new state creates physical nexus. Before hiring in a new state, factor in the sales tax registration requirement.

Trade Shows and Events

Selling at trade shows, pop-ups, or conferences can create temporary physical nexus. Check state rules before you exhibit.

Affiliate Programs

Affiliates and referral partners in certain states may create affiliate nexus for your business. Know where your affiliates operate.

Economic Threshold Creep

If you monitor thresholds only once a year, you might miss when you should have registered months earlier. Set up monthly or quarterly reviews of sales by state. Consider building this into your financial planning cycle.

Frequently Asked Questions

Q: If I hit an economic nexus threshold mid-year, when do I start collecting?

A: This varies by state. Some require collection from the threshold date; others give 30 days notice or allow collection to begin next fiscal period. Check your state's rules. Once you register, the state will clarify.

Q: Do I owe back sales tax on sales before I registered?

A: In most cases, yes. If you had nexus but didn't know it, you typically owe back tax, plus interest and penalties. This is where a voluntary disclosure agreement (coming forward proactively before audit) is invaluable. It usually caps look-back to 3-4 years and reduces or eliminates penalties.

Q: My state has no sales tax. Do I still have nexus in other states?

A: Yes. Nexus is state-by-state, not based on your home state. If you have physical presence or hit economic thresholds in other states, you have nexus there regardless of your own state's tax environment.

Q: Does nexus apply to business-to-business sales?

A: Generally no. B2B sales are often exempt if the buyer provides a reseller's permit or exemption certificate. However, some states carve out exceptions, and some B2B services are taxable. Know the rules for your specific offerings.

Q: Can I lose nexus if my sales drop below the threshold?

A: Losing nexus is usually harder than gaining it. Most states require you to remain registered once established, even if sales drop. Some allow closure if you're below threshold for a full calendar or fiscal year. Check with each state.

Q: Do I need a separate accountant for each state's sales tax?

A: No. But you do need visibility into sales by state and a reliable way to file and remit in multiple jurisdictions. Many small business accountants handle multi-state sales tax. Alternatively, use a sales tax automation service that integrates with your e-commerce platform.

Q: What if I'm unsure whether I have nexus in a particular state?

A: Contact the state's department of revenue or consult a multistate tax professional. It's far cheaper to clarify upfront than deal with audit. Many states won't penalize you if you come forward voluntarily and correct the mistake.

Managing Multi-State Compliance Going Forward

As your business grows—new employees in new states, new fulfillment arrangements, expansion to new sales channels—your nexus exposure shifts. Make nexus assessment part of your annual business planning cycle, not a one-time checkbox. Especially if you're managing accounts across multiple locations.

Without automation, you're doing the same filing, remittance, and record-keeping work in parallel for each state. That's how small business owners end up filing late, missing thresholds, or discovering years later they owed tax never collected.

Use accounting software that supports multi-jurisdiction tracking to flag nexus thresholds, calculate the correct rate for each transaction, and file across all registered states. Many platforms now integrate with your cash basis or accrual accounting system and streamline the multi-state reporting.

Stay aware. When in doubt, ask the state directly.