How Sales Tax Works for Online Sellers: 2026 Guide

Why Online Sellers Owe Sales Tax in States They Have Never Visited

Sales tax in the United States is not a single national tax — it is a patchwork of state and local rules. Historically, a seller only collected tax where it had a physical presence: an office, warehouse, or employee. That changed with the 2018 South Dakota v. Wayfair Supreme Court decision, which let states require collection based on economic nexus — simply selling enough into a state, even with no physical footprint there.

Today, nearly every state with a sales tax has an economic nexus threshold, typically measured as a dollar amount of sales or a number of transactions into the state per year. Cross the threshold and you generally must register, collect, and remit. This is general information, not tax advice — thresholds and rules change, so verify against your state's current revenue department guidance or consult a tax professional.

Sales tax directly affects your pricing and margins, so model it alongside your other costs in our Shopify Profit Calculator or eBay Profit Calculator depending on where you sell.

Economic Nexus: The Threshold That Creates Obligations

Economic nexus laws generally use two kinds of triggers: a revenue threshold (for example, $100,000 in sales into the state is a common figure, though it varies) and sometimes a transaction count threshold. Exceed either in the measurement period and nexus is typically established. Some states have dropped the transaction-count test entirely, relying on revenue alone.

Key nuances sellers miss:

• Thresholds usually include all sales, not just taxable ones — exempt or wholesale sales can still count toward the total in many states.
• The measurement period varies — calendar year, rolling twelve months, or the prior fiscal year depending on the state.
• Nexus is sticky. Once established, you generally remain obligated even if sales later dip below the threshold, until you formally close the registration.
• Digital products are taxed differently — some states tax them fully, others exempt them, and a few have special digital-goods rules.

Marketplace Facilitator Laws: When the Platform Collects for You

If you sell on Amazon, eBay, Etsy, or Walmart Marketplace, you have likely noticed the platform adding tax at checkout. Marketplace facilitator laws — now in effect in nearly all states with sales tax — make the marketplace itself responsible for collecting and remitting tax on third-party sales it facilitates.

This is a huge simplification, but it does not eliminate your obligations:

Situation	Who Collects?	Your Remaining Duty
Sales through a marketplace	The marketplace	Often none for those sales, but keep records proving the marketplace collected
Sales on your own website	You	Register, collect, file, and remit wherever you have nexus
Mixed marketplace + direct sales	Split	Track each channel separately; marketplace sales may still count toward nexus thresholds

A common trap: sellers assume marketplace facilitator laws mean they never need to register anywhere. But your own-site sales still create obligations, and in some states marketplace sales count toward the nexus threshold that triggers registration for your direct sales.

Registration, Collection, and Filing in Practice

Once you determine you have nexus in a state, the compliance cycle has three steps. Register for a sales tax permit with the state's revenue department — usually free or low-cost, done online. Collect the correct rate at checkout; rates combine state, county, and city components and can differ by ZIP code, so most sellers use automated tax software integrated with their store. File and remit on the state's schedule — monthly, quarterly, or annually depending on your volume — even for periods with zero taxable sales in some states.

Exemption certificates add another layer: if you sell to resellers or tax-exempt organizations, you must collect and validate their certificates to avoid charging tax you should not charge — or being liable for tax you failed to collect. Keep these documents organized; auditors ask for them first. Many sellers now store exemption certificates digitally alongside transaction records, so a multi-state audit request can be answered in hours rather than weeks — and missing certificates are the single most common source of unexpected assessments.

Penalties, Voluntary Disclosure, and Getting Help

States can assess back taxes, interest, and penalties for periods you should have been collecting but were not. Because the tax was supposed to come from the customer, you cannot simply "pay it later" without pain — the liability can exceed your margin on those sales. Many states offer voluntary disclosure programs that limit the lookback period and waive penalties if you come forward before they find you.

For most small sellers, the practical stack is: automated tax calculation at checkout, a filing service or accountant for multi-state registration, and a yearly nexus review as sales grow. Estimate the overall tax burden on your profits with our tax calculator, and remember — this guide explains the mechanics, but your specific obligations deserve professional advice.