When do state sales tax rules apply to your online business?

Quick answer: state sales tax rules typically apply when your business has “nexus” in a state. Nexus is any connection that gives a state legal authority to require the collection and remittance of sales tax — historically a physical presence, but since 2018 it commonly includes economic thresholds tied to sales revenue or number of transactions. (See South Dakota v. Wayfair, Inc., U.S. Supreme Court, 2018.)

Why this matters now

The U.S. Supreme Court decision in South Dakota v. Wayfair, Inc. (2018) changed the rules for remote sellers. The Court held that states may require out-of-state sellers to collect sales tax even without physical presence, so long as the state’s law does not place an undue burden on interstate commerce. After that ruling, states rapidly adopted “economic nexus” laws with thresholds that trigger collection obligations. That created a multi-state compliance challenge for online sellers.

Authoritative sources: SCOTUS opinion (South Dakota v. Wayfair, 2018); state revenue departments; guidance from the Streamlined Sales and Use Tax Agreement and the Tax Foundation for comparisons.

How nexus works for online sellers

  • Physical nexus: Traditional triggers such as a retail store, office, warehouse, employees, or inventory in a state. Using a third-party fulfillment center (like Amazon FBA) or storing returns in a state generally creates physical nexus.

  • Economic nexus: A threshold based on sales revenue or number of transactions into a state. Once you exceed that threshold in a state (often measured on a trailing 12-month basis), you must register to collect sales tax in that state.

  • Affiliate and click-through nexus: Having affiliates, referral arrangements, or agents in a state (or links placed by residents of a state that produce sales) can create nexus in some jurisdictions.

  • Marketplace facilitator laws: Many states require marketplaces (Amazon, Etsy, etc.) to collect and remit sales tax on behalf of marketplace sellers. That reduces obligations for some sellers but doesn’t eliminate registration or reporting requirements in all cases.

Note: specific thresholds and rules vary widely across states. South Dakota’s law (used in the Wayfair case) set a $100,000 sales or 200-transaction threshold; many states adopted similar $100,000 or transaction-based tests, while others use higher sales thresholds (some states use $250,000, $500,000 or another figure). Always check the current rule on the relevant state revenue website.

Examples from practice

  • Example 1: A craft seller based in Ohio uses a third-party logistics provider that stores inventory in Pennsylvania. The storage creates physical nexus in Pennsylvania. The seller must register with the Pennsylvania Department of Revenue, collect PA sales tax on taxable sales to Pennsylvania customers, and remit returns to PA.

  • Example 2: A digital subscription company sells SaaS nationwide. Many states exempt certain digital services, but rules differ. In states where subscriptions are taxable and sales exceed that state’s economic nexus threshold, the company must collect and remit sales tax.

  • Example 3: A small e-commerce store sells $50,000 annually into most states, but reaches $120,000 in sales in State A during the year. If State A’s economic nexus threshold is $100,000, that seller has triggered nexus and must comply there going forward.

(These examples are illustrative — confirm with state rules or a tax pro.)

What gets taxed (and common exemptions)

  • Tangible personal property: Most states tax physical goods sold to consumers.
  • Services: Tax treatment varies. Many states tax certain services (e.g., repairs, installation, digital services) and exempt others (e.g., professional services in some states).
  • Digital products: Some states tax downloads or streaming; others do not. Treat digital goods carefully and verify state-by-state rules.
  • Shipping & handling: States differ; some tax shipping when charged to the buyer and shipping is part of the sale, others exempt separately-stated shipping charges. Check individual state guidance.

Practical compliance checklist (step-by-step)

  1. Track sales by state and by transaction count on a rolling 12-month basis. Many states use that window for economic nexus tests.
  2. Determine where you have physical nexus — warehouses, employees, inventory, pop-up sales, or trade show activity.
  3. Check each state’s economic nexus threshold and effective date on the state revenue department website.
  4. Register for a sales tax permit only in states where nexus is established.
  5. Configure your checkout so it collects the correct rate (state + local), accounts for exempt customers, and handles shipping taxation per state rules.
  6. File returns and remit collections on time — frequency varies by state and can be monthly, quarterly or annually.
  7. Maintain records: sales invoices, exemption certificates, marketplace seller reports, and any use-tax statements for customers.
  8. Reassess each quarter; crossing a threshold mid-year usually creates immediate obligations.

Registration, collection and remittance: what to expect

  • Registration: Apply through the state’s department of revenue website. Registration requirements and processing times vary.
  • Collection: Calculate tax based on the customer’s delivery address (this is called ‘sourcing’). Some states tax where the sale is made, others tax destination — most states today use destination sourcing for retail sales.
  • Remittance and returns: Keep to the state’s filing schedule. States impose penalties and interest for late filings or underpayment.

See also: State Sales Tax Sourcing Rules: Where Sales Are Taxed and Why It Matters.

Marketplace facilitators — what to watch for

Marketplace facilitator laws require platforms like Amazon, eBay, Etsy and Shopify (when acting as facilitator) to collect and remit sales tax for sales made through their marketplace in many states. This can simplify compliance for marketplace sellers, but:

  • Confirm whether the marketplace reports sales to the seller or the state.
  • Some states still require sellers to register even if the marketplace collects tax (for reporting or exemption reasons).
  • Keep seller reports and 1099-K forms (if issued) for your records and for nexus analysis.

See also: Sales Tax Collection Best Practices for Online Sellers.

Recordkeeping and audits

Good records reduce audit risk and make it easier to respond to state notices. Keep:

  • Sales invoices and receipts with delivery addresses
  • Sales tax collected and remitted records
  • Exemption certificates (resale, nonprofit, government) with originals where possible
  • Marketplace facilitator reports and settlement statements

In an audit, states will look for unreported sales, missing registrations, and improperly claimed exemptions. Respond promptly to notices and work with a tax professional if contacted.

Common mistakes and how to avoid them

  • Mistake: Assuming no tax obligation unless you have a brick-and-mortar store. Avoid: Regularly check economic nexus thresholds and inventory locations.
  • Mistake: Not tracking transactions by state. Avoid: Use accounting or sales tools that break out sales by destination.
  • Mistake: Ignoring marketplace facilitator details. Avoid: Confirm whether the platform collects tax and how they report activity.

Tools and automation

Sales tax automation tools reduce manual errors by calculating rates at checkout, managing exemption certificates, and filing returns. Popular options integrate with major e-commerce platforms and can handle multi-state rules. Implement automation once you’re selling in multiple states to lower compliance costs.

FAQs (brief)

Q: How do I know when I cross an economic nexus threshold?
A: Track cumulative sales and the number of transactions into each state on a rolling basis and compare them to the state’s published threshold.

Q: Does the IRS administer state sales tax?
A: No. Sales tax is administered by state and local governments. The IRS handles federal taxes. For sales tax details, consult state revenue departments and state statutes.

Q: What happens if I don’t collect sales tax?
A: States can assess unpaid tax plus interest and penalties, and may audit multiple prior years. Some states offer amnesty or voluntary disclosure programs — check with the state revenue office.

Practical tips from a practitioner

  • Monitor sales monthly, not just annually. In my practice, early detection of nexus helped clients avoid large retroactive liabilities.
  • Keep software settings updated for sourcing and local rates; local surtaxes can materially change what you owe.
  • Treat exemption certificates like currency — collect, verify and store them securely.
  • If you use fulfillment partners (FBA, 3PL), identify where inventory is stored and treat each storage location as a potential nexus.

Conclusion

State sales tax for online businesses is an operational and legal obligation shaped by nexus, sourcing rules and state-specific thresholds. The landscape after Wayfair requires sellers to be proactive: track sales by destination, understand marketplace rules, register where required, and use automation to keep compliance manageable.

Professional disclaimer: This article is educational and does not constitute personalized tax or legal advice. For specific questions about nexus, registration, or state rules, consult a licensed tax advisor or the applicable state department of revenue.

Authoritative sources and further reading:

  • South Dakota v. Wayfair, Inc., Supreme Court of the United States (2018).
  • State department of revenue websites (search “[State name] Department of Revenue sales tax nexus”).
  • Streamlined Sales and Use Tax Governing Board — guidance on sourcing and simplification efforts.
  • Tax Foundation — summaries of state economic nexus thresholds and developments.

Internal resources:

If you want, I can prepare a simple spreadsheet template to track state-by-state sales and transactions that flags when you near common threshold levels.