Sales Tax For US E-commerce Sellers

Since the Supreme Court's South Dakota v. Wayfair decision, 45 states plus DC impose sales-tax obligations once your sales cross an economic threshold — commonly around $100,000 or 200 transactions in a state, though each state sets its own. Shopify and Amazon collect, but they don't register or file for you, and marketplace-facilitator rules don't cover your direct sales. Next Tax Source runs a full nexus study, registers you only where you genuinely owe, configures your tax engine, and files returns across every state — reviewed and signed by a licensed professional.

Who This Is For

Sales tax is the obligation online sellers are most likely to discover too late. It does not depend on having an office or staff in a state — economic activity alone can create it. The sellers who most need a deliberate sales-tax strategy tend to look like this:

• Direct-to-consumer brands on Shopify, WooCommerce or BigCommerce selling nationwide from a single warehouse.
• Amazon and multichannel sellers who assume the marketplace covers everything — and are exposed on their off-marketplace sales.
• Subscription and digital-goods businesses, where states increasingly tax software, SaaS and digital products in ways that vary wildly.
• Fast-growing startups that crossed economic thresholds in a dozen states before anyone was tracking it.
• Sellers with inventory in fulfilment centres, where stored stock can create a physical-presence obligation on its own.

How Economic Nexus Actually Works

Before Wayfair, a state could generally only require you to collect sales tax if you had a physical presence there. Wayfair changed that: states may now require collection based on economic presence alone — a level of sales or transactions into the state over a defined period. Two consequences follow, and both trip sellers up.

• Thresholds differ by state. Many use a figure around $100,000 in sales or 200 transactions, but the dollar amount, the transaction count, and the measurement period all vary, and some states have dropped the transaction test entirely.
• Physical presence still counts too. Inventory in a fulfilment centre, remote employees or contractors, or attending trade shows can create nexus regardless of your sales volume.
• Taxability is not uniform. Whether your specific product — clothing, food, software, a digital download — is taxable, and at what rate, changes from state to state and sometimes by locality.
• Registration triggers ongoing filing. Once you register, you must file on the state's schedule even in periods with zero sales, or face penalties.

Because thresholds and taxability rules change regularly, we verify each state's current position against its department of revenue rather than relying on a static table. For background on how the rules work generally, the IRS small-business resources are a useful starting point, though sales tax itself is administered state by state.

What Marketplaces Do And Don't Cover

Marketplace-facilitator laws require platforms like Amazon, eBay and Etsy to collect and remit sales tax on the sales they facilitate. That is genuinely helpful — but it is also where the dangerous assumption lives.

• The facilitator only covers sales through that marketplace. Your Shopify store, your own website and any wholesale or phone orders remain entirely your responsibility.
• Even where the marketplace remits the tax, some states still expect you to register and file a return reporting those sales, which is easy to overlook.
• Marketplace sales can still count toward your economic-nexus threshold in some states, pulling your direct sales into the net sooner than you expect.

Common Mistakes We Are Asked To Fix

Most sales-tax clean-ups trace back to a handful of recurring errors — and the longer they run, the more expensive they get.

• Assuming Amazon handles everything, leaving direct-channel sales uncollected and unreported.
• Over-registering in states where there is no obligation, creating needless filings and penalties for late zero returns.
• Ignoring inventory nexus created by stock sitting in a fulfilment centre.
• Collecting tax but never remitting it — holding trust funds the state will eventually demand, with interest.
• Waiting to be found instead of using a voluntary disclosure agreement, which usually limits the look-back period and waives penalties.

How Next Tax Source Handles It

We pair an always-on team of specialist AI agents with licensed human review. The agents pull your sales data, measure it against every state's current threshold, and flag the month you tip into nexus — before it becomes a back-tax problem. We register you only where you genuinely owe, configure your tax engine so collection is accurate at checkout, and prepare every return with a reconciliation back to your platform. A licensed CPA or Enrolled Agent reviews and signs the work before it is filed.

Where there is historic exposure, we negotiate voluntary disclosure agreements to limit the look-back and waive penalties. And because sales tax rarely sits in isolation, we coordinate it with your federal and state income-tax position — see our US tax accounting work — so the whole picture stays clean.

What To Prepare

A nexus study goes faster with a few inputs, but we can also pull most of this from your platforms once connected.

• Sales by state for the last 12–24 months (your platform can usually export this)
• Which channels you sell through — own store, Amazon, eBay, Etsy, wholesale
• Where your inventory is stored and where any staff or contractors are based
• Any states where you are already registered or collecting
• A description of what you sell, so we can assess taxability by state

You can also explore our US calculators while you gather the figures.

Questions People Ask