Picture a business headquartered in Ohio that sells products online to customers in 30 states. It has no office, warehouse or employee anywhere else, so the owner assumes it only needs to worry about Ohio sales tax. That assumption can be wrong. Since 2018, many states can require out-of-state sellers to register and collect sales tax based on their sales into the state alone.

Sales tax nexus is the connection between a business and a state that can create an obligation to register, collect and remit sales tax, depending on the state’s laws and the nature of the transactions. Nexus can come from physical presence, such as inventory or employees, or from economic activity, such as exceeding a state’s sales threshold. Each state sets its own rules, so the answer to “do we owe sales tax there?” has to be worked out state by state.

What Is Sales Tax Nexus?

Nexus is the threshold question: does this state have the right to require your business to collect its sales tax? It can arise in several ways:

• Physical nexus: a physical presence in the state, such as property, people or inventory.
• Economic nexus: sales into the state above a threshold set by that state.
• Marketplace facilitator rules: laws that shift collection on marketplace sales to platforms such as Amazon, which interact with a seller’s own obligations.
• Other state-specific provisions: such as affiliate or click-through rules in some states.

Nexus does not mean every sale is taxable. It is the first of five separate questions:

A business can have nexus in a state and still sell only exempt products there. Equally, a taxable product does not create an obligation in a state where you have no nexus.

Why Sales Tax Nexus Changed After the Wayfair Decision

For decades, a state could generally require a seller to collect sales tax only if the seller had a physical presence in the state, under the Supreme Court’s 1992 decision in Quill Corp. v. North Dakota. In South Dakota v. Wayfair, Inc., 585 U.S. 162 (2018), decided on June 21, 2018, the Court overruled that physical presence rule. It upheld South Dakota’s law requiring remote sellers with more than $100,000 in sales or 200 separate transactions into the state to collect tax, noting features of that law such as its small-seller threshold and no retroactive application.

Wayfair did not create a national rule. It allowed states to adopt economic nexus laws, subject to constitutional limits, and states then set their own thresholds, measurement periods and definitions. That patchwork is why multi-state sales tax compliance now needs a state-by-state approach.

The 5 Main Ways a Business Can Create Sales Tax Nexus

1. Physical Presence Nexus

Typical triggers include an office, store or warehouse; employees or sales representatives working in the state; inventory stored there; and in some cases contractors or agents acting on your behalf. What counts as physical presence, and whether brief or occasional activity is enough, depends on each state’s law and the facts. Economic nexus did not replace physical presence; both still apply.

2. Economic Nexus

A business can have nexus through economic activity alone. States use different threshold structures: total gross sales, retail or taxable sales only, number of transactions, or a combination. A common early model was $100,000 or 200 transactions, but many states use different amounts and several have dropped transaction tests. Never assume one figure applies everywhere.

3. Inventory Nexus

Inventory held in a state, whether in your own warehouse, a third-party logistics (3PL) provider’s facility or a fulfillment network such as Amazon FBA, is generally treated as physical presence. Because marketplaces may move inventory between warehouses, sellers should know where their stock sits and review each relevant state’s rules and the exact fulfillment arrangement.

4. Employee, Contractor or Agent Nexus

People who act on your behalf in a state, such as remote employees, independent sales representatives, installation or service personnel, and certain agents, can create nexus depending on state law. Not every contractor automatically does; the activities they perform and the relationship matter.

5. Affiliate and Other State-Specific Rules

Some states have additional provisions involving affiliated companies, in-state referral or click-through arrangements, or other activities. These rules vary significantly, so review the specific state’s statutes and guidance rather than relying on a nationwide assumption.

What Is Economic Nexus?

Economic nexus means a state can require a remote seller to collect its sales tax once the seller’s sales into the state exceed a threshold, even without any physical presence. States use it to apply the same collection obligations to remote and in-state sellers.

Thresholds differ in three main ways:

• The amount: for example, $100,000 in some states and $500,000 in others.
• What is measured: gross sales, taxable or retail sales only, and in some states a transaction count, sometimes required together with the dollar test.
• The measurement period: the previous calendar year, the current or previous calendar year, the preceding 12 months, or the previous four sales tax quarters.

To apply a threshold correctly, you need to know for each state which sales count, which transactions count, whether exempt, wholesale or resale sales are included, whether marketplace sales are included, and whether services are counted. Verify these against the state’s own guidance before reaching a conclusion.

Do All Sales Count Toward Sales Tax Nexus?

No. You should not simply add up every invoice. Depending on the state, the calculation may treat differently: taxable sales, exempt sales, sales for resale, wholesale transactions, marketplace-facilitated sales, services, digital products, SaaS subscriptions and intercompany transactions.

Marketplace Facilitator Laws and Sales Tax Nexus

Every state with a statewide sales tax now has marketplace facilitator rules that generally require platforms such as Amazon, eBay, Walmart Marketplace and Etsy to collect and remit sales tax on sales they facilitate, once the platform meets the state’s requirements.

That does not necessarily end the seller’s obligations. Consider separately:

• Direct website sales: the marketplace does not collect on these.
• Threshold calculations: some states include marketplace sales in the seller’s threshold and others exclude them. Washington and New York, for example, say marketplace sales are included.
• Physical presence: inventory in fulfillment centers can create nexus regardless of who collects on marketplace sales.
• Registration and filing: some states require marketplace-only sellers to register or file; others, such as Texas, do not require a permit where the marketplace handles all collection, but still require records to be kept.

When Does a Business Need to Register for Sales Tax?

1. Determine whether nexus exists in the state, physical or economic.
2. Determine whether your products or services are taxable there.
3. Determine whether registration is required under that state’s rules.
4. Register with the state tax authority.
5. Begin collecting tax from the date the state requires.
6. File returns and remit on the schedule the state assigns.

Timing matters. Some states require collection from the next transaction once you cross the threshold; others allow a short period. Texas, for example, requires collection to begin no later than the first day of the fourth month after the month the seller exceeds its threshold. Having customers in a state, on its own, is not a reason to register.

Sales Tax Nexus Examples

These are hypothetical scenarios for illustration, not tax advice.

Example 1: Online retailer. A California business sells $150,000 of products spread across many states. California’s rules say nothing about other states, so the business needs a state-by-state review. It may exceed a $100,000 threshold in a state where it sells heavily, even though its total looks modest.

Example 2: Amazon seller. A seller uses a fulfillment network that stores inventory in several states. Each state where inventory sits should be evaluated for physical presence, separately from any economic nexus analysis.

Example 3: SaaS business. A SaaS company sells subscriptions nationwide. It must ask two questions in each state: does it have nexus, and is SaaS taxable there? States differ widely on taxing software and digital services.

Example 4: Consulting business. A consultant travels to client sites in another state. Whether that travel creates physical presence, and whether the consulting service is taxable at all, both require state-specific analysis.

Example 5: Marketplace plus direct sales. A brand sells through Amazon and its own Shopify store. Amazon may collect on marketplace orders, but the brand must analyze its direct sales separately and check whether each state counts marketplace sales toward its threshold.

Sales Tax Nexus by State: Selected Examples

Swipe the table sideways to see all columns.

This table is a starting point, not a substitute for a state-by-state nexus analysis. Thresholds and definitions change, so confirm each state’s current rule on its official website before acting.

Sales Tax Nexus vs. Income Tax Nexus

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Having sales tax nexus does not automatically mean you have income tax nexus in the same state, and the reverse is also true. Each needs its own analysis.

Common Sales Tax Nexus Mistakes

1. Assuming no office means no nexus. Economic nexus can apply without any physical presence.
2. Using one nationwide $100,000 threshold. Check each state’s actual figure and test.
3. Ignoring marketplace sales. Some states count them toward your threshold.
4. Ignoring inventory in other states. Fulfillment center stock can create physical nexus.
5. Forgetting remote employees. One employee working from home in a state can matter.
6. Assuming all products are taxed the same. Taxability differs by product and state.
7. Assuming services are never taxable. Many states tax some services.
8. Registering too late. Uncollected tax can become the seller’s cost.
9. Not filing zero returns where required. Registration usually brings filing obligations even with no sales.
10. Not tracking sales by state. You cannot monitor thresholds without the data.
11. Ignoring threshold changes. States do amend their rules; review periodically.
12. Assuming marketplace collection covers everything. Direct sales and registration duties may remain.

How to Perform a Sales Tax Nexus Review

1. Map your business activity: locations, employees, contractors, inventory, warehouses, fulfillment centers, marketplaces, website sales, customer locations and service locations.
2. Export sales by state for the historical periods relevant to each state’s measurement rules.
3. Categorize sales: taxable, exempt, wholesale, resale, marketplace, services and digital products.
4. Compare against current state rules for each relevant state.
5. Determine nexus and registration dates: when nexus began and when obligations may have started.
6. Review filing history: which required returns were filed.
7. Identify exposure: unregistered states, uncollected tax, late filings, incorrect rates and missing exemption certificates.
8. Create a remediation plan: prioritize states by facts, exposure and deadlines, and consider available voluntary disclosure options.

What Happens If You Should Have Collected Sales Tax but Didn’t?

If a business had an obligation it did not meet, it may face registration requirements, past-due returns, tax assessments, interest and penalties, plus the practical problem that the tax usually cannot be recovered from past customers. It may also face greater audit exposure. Consequences vary by state and circumstances.

Remediation options may include registering going forward, filing past-due or amended returns, and voluntary disclosure agreements (VDAs), which many states offer and which may limit look-back periods or reduce penalties. Terms differ by state, and the Multistate Tax Commission runs a multistate voluntary disclosure program for participating states. Professional advice is valuable before approaching any state.

When Should You Hire a Sales Tax Nexus Consultant?

A sales tax nexus consultant can be useful when you sell into many states, are growing quickly online, combine marketplace and direct sales, hold inventory in multiple states, have remote employees, sell SaaS or digital products, are acquiring a business, are expanding into new states, are unsure about historical nexus, suspect uncollected tax exposure, or have received a state notice or audit letter.

Depending on the firm, support may include nexus analysis, state registration, taxability research, historical exposure reviews, return filing processes, voluntary disclosures, exemption certificate management, sales tax technology selection and audit support. Not every consultant offers all of these, so confirm scope up front.

Sales Tax Nexus Self-Assessment Checklist

• Do we sell to customers in multiple states?
• Do we have employees working in other states?
• Do we hold inventory outside our home state?
• Do we use third-party fulfillment?
• Do we sell through marketplaces?
• Do we know our sales volume by state?
• Have we reviewed each state’s economic nexus threshold?
• Do we know whether our products or services are taxable in each state?
• Are we registered where required?
• Are we filing all required returns?
• Are exemption and resale certificates properly maintained?
• Have we reviewed nexus rules in the last 12 months?

This checklist is a screening tool and does not determine whether a business has a legal sales tax obligation.

Frequently Asked Questions

Know Where You Owe Before a State Tells You

Having customers in another state is only the starting point. A business needs to evaluate nexus, product and service taxability, registration requirements, collection obligations and filing requirements on a state-by-state basis. Economic nexus has made this especially important for e-commerce, SaaS and other multi-state businesses.

This article is for general educational purposes and is not tax or legal advice. State rules change; verify current requirements with each state’s tax authority.

Sources & References (official): South Dakota v. Wayfair (U.S. Supreme Court) · California CDTFA · New York Department of Taxation and Finance · Texas Comptroller · Florida Department of Revenue TIP 21A01-03 · Washington Department of Revenue. Supporting: Multistate Tax Commission · Streamlined Sales Tax