What Is Sales Tax Nexus? A Practical Guide for E-Commerce and SaaS Businesses

As your growing business crosses state lines, a quiet obligation follows: sales tax nexus.

This is the legal connection between your business and a state that determines whether you must register, collect, and remit sales tax there. And for most growing e-commerce and SaaS businesses, it triggers in more states than they expect.

What most guides don't tell you upfront is how the rules have changed. Today, selling enough into a state, even without a single employee or warehouse there, can be enough to create a legal tax obligation. Many businesses are already past the threshold and don't know it yet.

This guide breaks down exactly how sales tax nexus works, what types of nexus exist, when your obligations begin, and what it actually takes to stay compliant as you scale. By the end, you'll know precisely where your business stands, and what to do about it.

What is "Nexus" in Sales Tax and What Does It Mean?

Sales tax nexus occurs when a business has a sufficient connection to a state or taxing jurisdiction. That connection triggers a legal obligation: you must register with the state, charge sales tax on taxable sales, and file returns on a set schedule.

The term "nexus" comes from tax law and simply means "link" or "connection." Once that link exists, your tax obligations in that state begin.

Different states have different definitions of what creates nexus. There is no single national standard. As a remote seller operating across multiple states, you are responsible for understanding each state individually.

How Does Nexus Work in a State?

A state's nexus rules determine when an out-of-state seller has a sales tax collection obligation within its borders. Each state sets its own:

• Thresholds — the dollar amount or transaction count that triggers nexus
• Sourcing rules — whether tax is based on origin or destination
• Effective dates — when obligations begin after a threshold is crossed
• Filing frequencies — monthly, quarterly, or annual returns

Nexus can be triggered prospectively, meaning once you cross a threshold, obligations start going forward, or retroactively, depending on state law. Some states apply nexus from the moment a threshold is crossed during the previous calendar year. Others apply it from the following calendar year. These differences matter when determining when you should have started collecting.

Not sure where you have nexus? Run Taxolio's free Nexus Checker — it takes under two minutes to confirm which states require action.

Types of Sales Tax Nexus

1) Physical Nexus

Physical nexus is created when a business has a tangible presence in a state. This is the traditional standard that governed sales tax law before 2018.

Physical presence includes:

• A store, office, or warehouse in the state
• Employees or on-site contractors working in the state
• Regular attendance at trade shows or events
• Inventory stored in a third-party fulfillment center, including Amazon FBA warehouses

That last point surprises many e-commerce businesses. Storing inventory in a fulfillment warehouse commonly creates physical nexus for the inventory owner, even if the business has no other footprint in that state. If you use FBA or a third-party logistics provider, check where your inventory sits.

2) Economic Nexus

Economic nexus is created when a business has a certain level of economic activity in a state — even without any physical presence there.

The U.S. Supreme Court's 2018 decision in South Dakota v. Wayfair, Inc changed everything. The ruling allows states to require out-of-state sellers to collect and pay sales tax based purely on economic activity. Before Wayfair, a business had to have a physical footprint in a state before that state could require tax collection. That is no longer true.

Today, most states have adopted economic nexus laws. Common thresholds include:

• $100,000 in sales in the state during the current or previous calendar year
• 200 transactions in the state during the same period
• Some states require meeting both thresholds; others use either one

Economic nexus thresholds and rules vary by state and change frequently. Tracking effective dates prevents unexpected liabilities from catching you off guard.

3) Other Nexus Triggers

Beyond physical and economic presence, other factors can create sales tax nexus obligations:

• Affiliate nexus — an in-state affiliate that generates sales or referrals on your behalf
• Click-through nexus — a referral relationship where an in-state third party drives sales through commission-based links
• Marketplace nexus — selling through platforms like Amazon or Etsy, where marketplace facilitator laws may require the platform to collect tax on your behalf

Marketplace facilitator rules vary by state. In many states, the platform collects and remits sales tax on seller transactions. However, not all sales on all platforms are covered, so confirm what remains your responsibility.

What Are Your Sales Tax Nexus Obligations?

Once a sales tax nexus is established, your obligations follow a clear sequence:

1) Register for a Sales Tax Permit

You must register with each state's tax authority before you begin collecting tax. Collecting sales tax without a valid permit creates its own compliance risk. Registration requirements, timelines, and accepted methods differ by state.

2) Collect the Correct Sales Tax Rate

After registering, you must charge sales tax at the correct rate for each taxable sale. The correct amount depends on:

• The product or service being sold (taxability varies — digital goods and SaaS are taxed differently across states)
• The customer's delivery location (destination-based sourcing applies in most states)
• The combined state plus local sales tax rate for that jurisdiction

Local sales tax rates can vary significantly within a single state. A sale shipped to a city in Texas carries a different combined rate than a sale shipped to a rural county in the same state.

3) Remit Sales Tax to Each State

Collecting tax is only half the obligation. You must also pay sales tax to each state on the schedule that state requires — monthly, quarterly, or annually — depending on your sales volume.

4) File Sales Tax Returns

Businesses with nexus are responsible for filing the applicable sales tax returns in every state where they have a collection obligation. This includes zero returns — filings that report no activity — where states require them even in months with no taxable sales.

Taxolio handles registrations, filings, and zero returns across all states you're active in. Book a free consultation to confirm your obligations and get a clear path to compliance.

How to Determine If You Have Sales Tax Nexus

Follow these steps to find out if you have sales tax nexus in your business.

Step 1) Inventory Your Physical Footprint

List every location where your business has property, employees, contractors, or stored inventory. Include third-party warehouses and fulfillment centers. This identifies states where physical nexus may already exist.

Step 2) Run a State-by-State Sales Report

Pull detailed sales data by shipping or billing address. For each state, calculate:

• Total sales revenue from buyers in that state
• Total number of transactions to buyers in that state

Compare these figures against each state's economic nexus threshold and effective dates.

Step 3) Check Marketplace Activity

If you sell through Amazon, Etsy, Shopify, or other platforms, confirm which states require the marketplace to collect on your behalf — and which obligations still fall on you.

Step 4) Consult State Guidance for Edge Cases

Specific rules apply to bundled services, digital products, SaaS subscriptions, and other non-standard offerings. Taxability rules for these product types differ significantly by state. Consult state guidance or a qualified tax advisor for any situation that doesn't fit a simple product-sale model.

Use Taxolio's Nexus Checker to run a fast assessment of where your business likely has nexus based on your sales activity. Try it free here.

Economic Nexus Laws & How States Differ

Each state sets its own economic nexus threshold, effective date, and lookback period. Here's what varies across states:

States update economic nexus laws regularly. What was compliant last year may not be compliant today. Staying current with changes in each state where you sell is an ongoing requirement, not a one-time task.

What Happens If You Don't Comply?

Failing to manage sales tax obligations properly can result in:

• Back-tax assessments — states can pursue unpaid sales tax for open audit periods
• Penalties — for failing to register, collect, or remit on time
• Interest charges — accruing from the date tax was due
• Increased audit exposure — states use data matching and third-party information to identify noncompliant sellers

Voluntary disclosure programs exist in many states and can reduce penalties for businesses that come forward before being contacted by the state. These programs typically require prompt registration and remediation. Acting early is almost always less costly than waiting.

Already behind on compliance? Book a free call with Taxolio — we'll confirm your exposure and map the cleanest path to getting current.

Recordkeeping and Audit Readiness

Good recordkeeping is not optional. To stay compliant and audit-ready, businesses should:

• Retain sales invoices and exemption certificates for the full statutory audit period (typically 3–4 years, but varies by state)
• Document nexus determinations — record what data you used, when you evaluated it, and what conclusion you reached
• Reconcile collected tax to filed returns monthly or quarterly to catch discrepancies before they become audit findings
• Track threshold calculations so you can demonstrate when economic nexus was first triggered in each state

Detailed records of all sales and taxes collected are essential for compliance with sales tax nexus laws. In an audit, the burden of proof falls on the business.

A Quick-reference Checklist for Sales Tax Nexus Compliance

Use this checklist to assess and manage your sales tax nexus obligations:

Identify your nexus exposure:

• Inventoried all physical locations, employees, and third-party warehouses
• Run state-by-state sales reports for current and previous calendar year
• Compared sales and transaction counts against each state's economic nexus threshold
• Reviewed marketplace facilitator rules for platforms you sell through

Meet your compliance obligations:

• Registered for sales tax permits in all states where nexus exists
• Configured systems to collect the correct local sales tax rates based on delivery location
• Set up remittance schedules per state requirements
• Filing returns (including zero returns) on time in all required states

Maintain audit readiness:

• Retaining sales records, exemption certificates, and nexus determinations
• Reconciling collected tax to filed returns each period
• Monitoring state law changes that could affect thresholds or taxability rules

Frequently Asked Questions (FAQs)

Did the Supreme Court change the rules for sales tax nexus?

Yes, fundamentally. In South Dakota v. Wayfair, Inc. (2018), the U.S. Supreme Court overruled Quill Corp. v. North Dakota (1992) and held that physical presence is no longer required to establish sales tax nexus. Under Quill, states could only require tax collection from sellers with a physical footprint in the state. Wayfair eliminated that protection entirely.

Today, a remote seller with no office, warehouse, or employee in a state can still owe sales tax there — purely based on the volume of sales or transactions made to buyers in that state. If you sell across multiple states and haven't reassessed your nexus exposure since 2018, your obligations may have changed significantly.

Do I need software or a specialist to manage multi-state sales tax compliance?

Both can help, but they solve different problems. Tax calculation software handles the math at the point of sale. What most software does not handle is the full compliance workflow: state registrations, return preparation, deadline management, and zero filings.

Many states have adopted economic nexus laws that require businesses to register, collect, and file in each state individually. Managing that across multiple states requires either dedicated internal resources or a specialist firm. Businesses that rely on software alone often find compliance gaps when they get audited.

A done-for-you service like Taxolio handles registrations and filings end-to-end, so nothing falls through the cracks. Book a free call to see what your current gaps look like.

How do economic nexus thresholds work across states?

Each state sets its own economic nexus threshold independently. Most states use $100,000 in annual sales or 200 transactions as the trigger.

But not all states follow this exact model. Some have removed the transaction threshold entirely and rely only on revenue. Others use different dollar amounts or apply the threshold to the previous calendar year rather than the current one.

Once you cross a state's threshold, you generally must register, begin collecting the correct local sales tax rates, and file returns on that state's schedule. Because thresholds and rules change frequently, tracking each state individually is an ongoing task.

Run Taxolio's Nexus Checker to see which states you've likely crossed based on your current activity.

What's the difference between sales tax software and a full-service compliance provider?

Sales tax software automates the calculation and collection of tax at the point of sale. It determines the correct rate for each transaction based on the buyer's location and the product being sold. That is genuinely useful, but it covers only part of the obligation. Registering in new states, preparing and filing returns, managing filing calendars across jurisdictions, and handling zero returns all require separate action.

General accounting software typically does not manage these tasks either, particularly across many states at once. A specialist compliance provider handles the full cycle: nexus review, state registrations, return preparation, filing, and ongoing monitoring as your business grows. For e-commerce and SaaS businesses scaling across states, this distinction matters.

How Taxolio Handles Sales Tax Nexus for You

Taxolio is a done-for-you sales tax compliance service built for e-commerce brands and SaaS businesses selling across multiple states. Rather than building internal tax operations or navigating state portals yourself, Taxolio manages the entire compliance workflow:

• Nexus review — confirms which states require action now versus later
• State registrations — prepared and submitted on your behalf
• Return preparation and filing — monthly, quarterly, and annual filings plus zero returns
• Ongoing monitoring — flags threshold changes and new obligations as your business grows

Taxolio works with U.S. and international businesses and offers transparent per-state pricing with no hidden fees.

Ready to know exactly where you stand? Run the free Nexus Checker or book a free consultation call — Taxolio will confirm your obligations and handle the rest.

Sales tax nexus requirements change frequently. This guide reflects general principles as of 2025. For state-specific guidance, consult the relevant state's department of revenue or a qualified tax professional.