What Is Sales Tax Nexus? A Guide for Multi-State Businesses | KealyWalker

Most companies do not know they have a nexus problem until a state finds it for them. By then, the question is not whether you owe — it is how many years back the clock runs.

Sales tax nexus is the legal connection between your business and a state that requires you to collect and remit sales tax there. Get it wrong — by ignoring it, misunderstanding it, or simply not keeping up as the rules change — and you are looking at back taxes, interest, and penalties calculated from the date your obligation began, not the date you discovered it.

This guide explains exactly how sales tax nexus works in 2026, what triggers it, how the rules differ by state, and what your business should do if you think you may have exposure you have not yet addressed.

Key takeaway

Since the Supreme Court's 2018 South Dakota v. Wayfair decision, you can have a sales tax obligation in a state you have never set foot in. Economic activity alone — crossing a state's revenue or transaction threshold — is enough. As of 2026, every state with a sales tax has economic nexus rules in place.

What Is Sales Tax Nexus?

Nexus — from the Latin for "connection" — is the legal standard that determines whether a state can require your business to collect and remit sales tax on transactions made to customers in that state. Without nexus, a state cannot compel you to collect. With nexus, the obligation is immediate and ongoing.

For most of U.S. history, nexus required physical presence: an office, a store, a warehouse, employees, or equipment in the state. A business selling from New York to customers in Ohio had no Ohio sales tax obligation unless it had some form of physical footprint there. That changed fundamentally in 2018.

The Wayfair Decision Changed Everything

On June 21, 2018, the Supreme Court decided South Dakota v. Wayfair, Inc., overturning a 1992 ruling that had limited states to taxing only sellers with physical presence. The Wayfair decision held that states can require sales tax collection based on economic activity alone — sales volume, transaction counts, or both — regardless of whether the seller has any physical presence in the state.

The practical consequence: if your business sells goods or certain services into a state above that state's threshold, you have nexus, you are required to register, and you are required to collect and remit sales tax. Whether you know about it or not.

Within months of the Wayfair decision, states moved rapidly to enact economic nexus laws. By 2026, every state that imposes a sales tax has an economic nexus framework. The thresholds, measurement periods, and specific rules vary — but the principle is uniform.

The Two Types of Sales Tax Nexus

Physical Nexus

Physical nexus — the original standard — is created by having a tangible presence in a state. Common physical nexus triggers include:

• A retail location, office, or showroom

• A warehouse or distribution center — including third-party fulfillment centers

• Remote or traveling employees, contractors, or sales representatives

• Inventory stored in the state, including through Amazon FBA or other 3PL networks

• Equipment or property located in the state

• Attendance at trade shows or events, in some states

Physical nexus does not require a permanent facility. A single employee working remotely from a state can create nexus. Inventory at a third-party logistics warehouse — including Amazon fulfillment centers — creates physical nexus in the state where that warehouse sits, independent of whether you have crossed any economic threshold. This catches e-commerce sellers off guard more than any other nexus trigger.

Economic Nexus

Economic nexus is triggered by sales activity into a state that exceeds a defined threshold — typically a dollar amount of revenue, a number of transactions, or both — during a defined measurement period, usually the prior or current calendar year.

The most common threshold, established by South Dakota in the case that bears its name, is $100,000 in annual sales or 200 separate transactions into the state. Most states adopted this standard following Wayfair. But 2026 has brought meaningful variation.

2026 update: transaction thresholds are disappearing

As of January 2026, 16 states have eliminated the 200-transaction threshold and now use revenue-only thresholds. Illinois removed its transaction threshold on January 1, 2026. Kentucky will remove its on August 1, 2026. If your prior nexus analysis relied on transaction counts to stay under a threshold in these states, that analysis needs to be updated.

Economic Nexus Thresholds Vary Significantly by State

Not every state uses the $100,000 / 200-transaction standard. Several major states apply substantially different thresholds.

Two critical nuances: First, some states require you to meet only one threshold to have nexus; others — including New York — require you to meet both the revenue and transaction threshold. Second, the measurement period matters. Some states look at the prior calendar year; others look at a rolling 12-month period; others look at either the current or prior year, whichever triggers first.

These differences mean that a business with nexus in 20 states cannot apply a single rule set. Each state requires its own analysis.

What Triggers Economic Nexus — and What Counts Toward the Threshold?

Beyond the headline threshold numbers, the specific transactions that count toward a state's nexus threshold vary. Understanding what is and is not included matters, particularly for businesses with a mix of taxable and exempt sales.

What generally counts

• Retail sales of tangible personal property shipped to customers in the state

• Sales of taxable digital goods and services, in states that tax them

• Marketplace sales, in many states — even if a marketplace facilitator is collecting the tax on your behalf

• Exempt sales, in most states — the sale counts toward the threshold even if no tax is owed

What generally does not count

• Sales for resale (though the exempt sale may still count toward the threshold in some states)

• Sales made through a marketplace facilitator where the facilitator is legally responsible for collection — in some states

• Sales of services that are exempt in the destination state

The marketplace facilitator question is particularly important for businesses that sell through Amazon, Etsy, eBay, or similar platforms. In most states, marketplace sales count toward your economic nexus threshold even though the platform is collecting the tax. You may be registered in fewer states than you technically have nexus in.

How Economic Nexus Interacts with Physical Nexus

Physical and economic nexus operate independently. If you have physical nexus in a state — because you have employees, inventory, or property there — you have nexus regardless of your sales volume. The economic nexus threshold is irrelevant once physical nexus exists.

The practical consequence: a business that has crossed the economic nexus threshold in a state but has no physical presence there has nexus based on economic activity. A business with a remote employee in a state but $50,000 in annual sales there has physical nexus regardless of whether it crossed the economic threshold.

Both types of nexus create the same obligation: registration, collection, and remittance.

The 3PL nexus trap

If you use Amazon FBA, or any third-party fulfillment network, your inventory is physically stored in warehouses across multiple states. That physical inventory creates physical nexus in each state where a warehouse holds your goods — independent of your sales volume into that state. Many e-commerce sellers have nexus in 15 to 20 states from their fulfillment network alone and do not know it. A nexus study that does not account for your fulfillment footprint is incomplete.

What Happens After Nexus Is Established

Once you have nexus in a state — whether physical or economic — a sequence of obligations follows:

1. Registration

You are required to register with the state tax authority before you begin collecting sales tax. Most states call this a Sales Tax Permit, a Seller's Permit, or a Certificate of Authority. Registration is required before collection begins — collecting without a permit creates its own exposure.

The registration process, timeline, and requirements vary by state. Some states issue permits immediately online. Others take weeks. Some require a security deposit. A few require in-state registered agents.

2. Rate determination

Sales tax rates are not uniform. They are set at the state level, the county level, the city level, and in some states, at the special taxing district level. The rate that applies to any given transaction depends on the delivery address of the buyer — not the location of your business.

A single zip code can contain multiple taxing jurisdictions with different rates. In states like Louisiana, Colorado, and Alabama, local rate complexity is significant. Getting the rate wrong — even by fractions of a percent — creates exposure on every transaction.

3. Filing cadence

Each state assigns a filing frequency based on your estimated or actual sales tax liability in that state: monthly, quarterly, or annually. That frequency is not fixed — as your sales volume grows, states reassign you to a more frequent filing schedule. Missing a reassignment and continuing to file quarterly when a state has moved you to monthly creates late filing penalties even if the underlying tax was correct.

4. Remittance

Each filing must be accompanied by a remittance of the tax collected. The remittance must match the return — discrepancies generate notices. Many states require electronic filing and ACH payment for larger filers.

5. Exemption certificate management

If any of your customers are tax-exempt — resellers, manufacturers, government entities, nonprofits — you are required to collect valid exemption certificates from them and maintain them on file. Each state has its own form requirements, content requirements, and renewal schedules. An invalid or missing certificate shifts liability to you on audit.

The Statute of Limitations: How Far Back Can States Go?

In most states, the statute of limitations for sales tax assessment is three to four years. That means if you had nexus in a state for the past three years and never registered, the state can assess you for the full three years of uncollected tax, plus interest, plus penalties.

For businesses that have been selling across state lines since before 2018 and never revisited their nexus footprint, the potential lookback exposure can be material.

The most effective way to resolve historical exposure is through a Voluntary Disclosure Agreement — a formal agreement with the state in which you proactively come forward, typically receive a limited lookback period of two to three years, and may receive penalty abatement. We manage VDA processes for clients across all states.

Six Situations That Should Trigger an Immediate Nexus Review

If any of the following applies to your business, your nexus footprint deserves a review now rather than later:

• You have expanded sales into new states in the past two years and have not updated your nexus analysis

• You have started using a third-party fulfillment service, an Amazon FBA program, or any new warehouse arrangement

• Your annual revenue has grown significantly — crossing state thresholds that were previously out of reach

• You have hired remote employees or contractors in states where you do not currently collect sales tax

• You sell through a marketplace and have not confirmed whether marketplace sales count toward nexus thresholds in your customer states

• You have never had a formal nexus study conducted, and you sell in more than three or four states

What Is a Nexus Study and Do You Need One?

A nexus study is a structured analysis of your business activity — sales data, transaction counts, employee locations, fulfillment footprint, contractor relationships — across every state where you have any commercial presence. The output is a state-by-state determination of where you have nexus, where you have potential historical exposure, and where you are clear.

A proper nexus study is not a self-assessment. It requires current knowledge of each state's rules, an understanding of how your specific business model, product mix, and sales channels interact with those rules, and access to your transaction data at the state-by-customer level.

At KealyWalker, we conduct nexus studies as the first step in every new client engagement. The study drives everything that follows: which states require registration, whether historical exposure warrants a VDA, and what the ongoing compliance calendar looks like.

Common nexus review mistake

Many businesses run a nexus review once — when they first cross a threshold — and do not revisit it. Nexus is not static. Your fulfillment footprint changes. Your sales volume grows. States change their rules. A nexus analysis that was accurate in 2022 may significantly undercount your current exposure. We recommend a formal nexus review at least annually for any business selling in more than five states.

How KealyWalker Approaches Sales Tax Nexus

KealyWalker manages the full sales tax compliance cycle — nexus studies, multi-state registration, monthly and quarterly filings, remittance management, exemption certificate programs, voluntary disclosure agreements, notice handling, and audit defense.

We are platform-agnostic. We connect to your existing billing system, ERP, or tax engine — NetSuite, Dynamics, Salesforce, QuickBooks, SureTax, or a custom-built platform — via data feed and take it from there. No system changes required.

Every client has direct access to the team managing their account. Flat-rate pricing. No per-filing or per-state fees.

• If you have reason to believe your nexus footprint is larger than your current registration reflects, the right time to address it is before a state initiates contact — not after. A 20-minute conversation is enough to understand where you stand.