Sales Tax Nexus: What Every Online Business Owner Must Know

If you sell products or certain services online, you may have sales tax obligations in states where you've never set foot — and you may not even know it.

This isn't a technicality. It's one of the most common and costly compliance gaps we see in growing e-commerce businesses. And since the 2018 Supreme Court ruling in South Dakota v. Wayfair, the rules changed dramatically.

Here's what you need to understand.

"Nexus" is the legal term for a sufficient connection between your business and a state that requires you to collect and remit that state's sales tax.

Historically, nexus was primarily physical — you had to have a store, warehouse, employee, or inventory in a state before that state could require you to collect sales tax. Remote sellers were largely exempt.

The Wayfair ruling changed that. Now, most states have economic nexus laws that apply to sellers based purely on sales volume — regardless of physical presence.

After Wayfair, states moved quickly to establish economic nexus thresholds. Today, 45 states plus Washington D.C. have sales tax, and virtually all of them have economic nexus rules.

The most common threshold: $100,000 in sales OR 200 transactions in a state within a calendar year.

Once you cross that threshold, you're required to:

1. Register for a sales tax permit in that state
2. Collect sales tax from customers in that state
3. File returns and remit the tax on schedule

Miss any of these steps, and you're exposed to back taxes, penalties, and interest.

Economic nexus didn't replace physical nexus — it added to it. You still have nexus in any state where you have:

• Employees or contractors (even remote workers)
• Inventory (including FBA inventory stored in Amazon warehouses)
• A warehouse or fulfillment center
• A physical office or retail location
• Trade show presence (in some states)

Many e-commerce sellers are surprised to learn that Amazon FBA creates nexus in every state where Amazon stores their inventory — which can be 20+ states.

Not everything is taxable in every state. Sales tax rules vary significantly:

• Physical goods are generally taxable, but there are exceptions (groceries, clothing, medicine)
• Digital products (software, ebooks, streaming) — taxability varies widely by state
• Services — most states don't tax services, but some do
• SaaS — increasingly taxable, but rules differ by state

Getting this wrong in either direction creates problems. Collecting tax you don't owe creates customer friction. Not collecting tax you do owe creates liability.

States take sales tax seriously because it's a significant revenue source. Penalties for non-compliance typically include:

• Back taxes on all uncollected sales tax (often going back 3–7 years)
• Penalties of 10–25% of the unpaid tax
• Interest that compounds over time
• Potential personal liability for business owners in some states

For a business that's been operating for several years without proper compliance, the total exposure can be substantial — sometimes six figures.

If you've discovered you have unfiled obligations in one or more states, voluntary disclosure is often the best path forward.

Most states have voluntary disclosure programs that allow businesses to come forward proactively in exchange for:

• Limited lookback periods (typically 3 years instead of the full statute of limitations)
• Penalty waivers in many cases
• A clean slate going forward

The key is acting before the state contacts you. Once a state initiates an audit or sends a notice, the voluntary disclosure window typically closes.

Step 1: Conduct a nexus study. Identify every state where you have physical or economic nexus. This requires reviewing your sales data, employee locations, and inventory placement.

Step 2: Determine taxability. For each state where you have nexus, determine which of your products or services are taxable.

Step 3: Register for permits. You must register in each state before you can legally collect sales tax. Operating without a permit is itself a violation.

Step 4: Configure your systems. Update your e-commerce platform, shopping cart, or billing system to collect the correct tax rates. Rates vary by state, county, and city.

Step 5: Address historical exposure. If you've had nexus in states without collecting, work with a tax advisor to assess your exposure and determine whether voluntary disclosure makes sense.

Step 6: Establish ongoing compliance. Set up a filing calendar and remittance process. Filing deadlines vary by state — some are monthly, some quarterly, some annually.

For high-volume sellers, manual sales tax management isn't practical. Platforms like Avalara, TaxJar, and Vertex integrate with most e-commerce systems to automate rate calculation, collection, and filing.

These tools are valuable, but they're not a substitute for understanding your nexus footprint. Automation only works correctly if it's configured based on accurate nexus analysis.

Sales tax compliance is one of the most complex and frequently overlooked areas of small business tax. The rules are different in every state, they change regularly, and the consequences of getting it wrong compound over time.

If you're selling online and haven't done a formal nexus review, now is the time. The longer you wait, the larger the potential exposure.

At ACM Tax Advisory, we conduct nexus studies, handle state registrations, manage voluntary disclosure filings, and set up ongoing compliance systems for e-commerce businesses of all sizes.

Not sure where you stand? Contact us for a sales tax compliance review. We'll identify your exposure and build a plan to get you clean.