Most e-commerce sellers don’t discover they have a sales tax problem until a state auditor sends a letter or a marketplace flags their account. By then, back taxes, interest, and penalties have already stacked up. The good news: cross-border sales tax compliance is entirely manageable if you understand the rules that actually apply to your business — not a generic summary of them. This guide gives you a concrete, sequential framework for figuring out your obligations, registering correctly, collecting accurately, and filing without mistakes.
Step 1: Understand What “Nexus” Actually Means for Your Business
Nexus is the legal connection between your business and a taxing jurisdiction that obligates you to collect and remit sales tax. Before the U.S. Supreme Court’s 2018 South Dakota v. Wayfair ruling, nexus required a physical presence — a warehouse, an employee, a trade show booth. That standard is now obsolete. Every U.S. state with a sales tax (45 states plus Washington D.C.) has adopted some version of economic nexus, and if you’re selling into those states, you likely have obligations you haven’t acknowledged yet.
Physical Nexus
You still have physical nexus if you store inventory in a state — including through Amazon FBA fulfillment centers. If Amazon warehouses your products in Kentucky, you have nexus in Kentucky. This catches a lot of FBA sellers completely off guard. Pull your inventory placement report and map every state where your stock sits.
Economic Nexus
Economic nexus thresholds vary by state, but the most common standard is $100,000 in sales or 200 separate transactions in a state within a calendar year. Some states, like California, have moved to a sales-only threshold of $500,000. Others, like Texas and Florida, apply the $100,000 threshold with no transaction count. Check each state individually — do not assume uniformity.
A practical starting point: pull your last 12 months of sales data by ship-to state. Any state where you crossed $100,000 in revenue or 200 transactions is almost certainly a nexus state for you. The Streamlined Sales and Use Tax (SST) Governing Board maintains updated threshold information for its member states and offers voluntary disclosure programs worth exploring if you’re registering late.
Step 2: Map Your Product Taxability
Not every product you sell is taxable in every state, and this is where a lot of sellers over-collect or under-collect. Getting taxability wrong in either direction creates liability.
Tangible Personal Property
Most physical goods are taxable, but there are meaningful carve-outs. Groceries are exempt or taxed at reduced rates in most states. Clothing is exempt in Pennsylvania, New York (below $110 per item), and Minnesota. Medical devices and prescription items are broadly exempt. If you sell in any of these categories, map your SKUs against each state’s exemption schedule — not just a high-level summary.
Digital Products
This is where international sellers and SaaS businesses get tripped up hardest. The taxability of digital goods — software, e-books, streaming subscriptions, downloadable files — varies wildly. Texas taxes most digital products. Florida, as of 2021, taxes certain SaaS and cloud services. Wyoming taxes digital audio and video. Several states tax nothing digital at all. If you’re selling any intangible digital product into the U.S., you need a state-by-state taxability map for your specific product type before you register anywhere.
Step 3: Register in Every Nexus State — Before You Collect
You cannot legally collect sales tax in a state where you haven’t registered. Collecting without registration is itself a violation, separate from failure to collect at all. Register first, then turn on tax collection in your platform.
The registration process differs by state. Most states now offer online registration through their Department of Revenue websites. Florida’s registration is handled through the Florida Department of Revenue, and the process typically takes 3–5 business days to receive your Certificate of Registration. Some states issue registration numbers immediately; others mail physical certificates. Track these timelines because you cannot file returns without the registration number.
If you’re registering in multiple states simultaneously — which is common when you first do a nexus audit — consider using the SST’s Centralized Registration system, which lets you register in all 24 SST member states with a single application.
Voluntary Disclosure Agreements (VDAs)
If you’ve had nexus in a state for years without registering, don’t simply register and start filing going forward. Many states will still audit you for the back period. Instead, contact the state’s VDA program first. Most states cap the look-back period to 3–4 years under a VDA (versus the full statute of limitations, which can run 6–7 years), and some waive penalties entirely. This is one of the highest-ROI compliance steps an e-commerce seller can take.
Step 4: Configure Your E-Commerce Platform Correctly
Tax collection is only as accurate as your platform configuration. Getting this right at setup saves you from years of correction headaches.
Origin vs. Destination Sourcing
Most states use destination sourcing: you charge the tax rate for the buyer’s location — their city, county, and state combined. Some states, including Texas and Illinois (for in-state sellers), use origin sourcing for certain transaction types. If you’re based in Illinois and selling to a customer in Chicago, you might charge based on your business address, not the customer’s address. Shopify, WooCommerce, and BigCommerce all have destination/origin sourcing toggles — confirm which mode is active for each state.
Product Tax Codes
Every major e-commerce platform uses product tax codes (PTCs) to apply exemptions automatically. Map each of your product categories to the correct PTC in your platform. If you’re selling a fitness supplement that’s exempt in some states as a “food product” but taxable in others as a “dietary supplement,” the PTC assignment determines which treatment applies. Review these assignments annually — state laws change, and a PTC that was correct two years ago may now produce incorrect results.
Marketplace Facilitator Laws
If you sell through Amazon, eBay, Etsy, or Walmart Marketplace, those platforms are required by law in virtually every U.S. state to collect and remit sales tax on your behalf. This does not eliminate your registration obligation in many states, but it does mean you should not also be collecting tax on those same transactions through your own checkout. Double-collecting creates refund liability and customer trust issues. Segment your channel reporting carefully.
Step 5: Manage International Sales Tax and VAT Obligations
If you’re an international seller shipping into the United States, or a U.S. seller shipping internationally, you face a separate but parallel set of obligations.
International Sellers Selling into the U.S.
Economic nexus applies to you regardless of where your business is incorporated. If a seller based in Germany ships $150,000 worth of goods to Texas buyers in a calendar year, that seller has Texas economic nexus and must register, collect, and remit Texas sales tax. The fact that you have no U.S. entity is irrelevant to the state’s enforcement position. The practical risk is lower in the short term — states can’t easily audit a foreign entity — but marketplace facilitator laws increasingly handle collection automatically, and the exposure grows as your U.S. revenue scales.
U.S. Sellers Shipping Internationally
The U.S. does not impose a federal VAT, but virtually every country you’re selling into does. The European Union’s One Stop Shop (OSS) system, launched in 2021, allows non-EU sellers to register once and cover VAT obligations across all 27 member states — provided your total EU sales are under certain thresholds. The standard threshold is €10,000 in cross-border B2C sales per year. Above that, you must either register for OSS or register individually in each EU country where you have customers. The UK, post-Brexit, operates its own separate VAT system; if you’re selling into the UK and your taxable turnover exceeds £85,000, you’re required to register for UK VAT.
Canada uses GST/HST at the federal level plus provincial sales taxes in most provinces. If you’re selling digital services into Canada and your worldwide revenue exceeds CAD $30,000, you have a GST registration obligation even without a Canadian business presence.
Step 6: File Returns Accurately and On Time
Filing frequency is assigned by the state based on your expected tax liability, and it varies. High-volume sellers often file monthly; smaller sellers may file quarterly or annually. Missing a filing deadline triggers automatic penalties — typically 5–10% of the tax due per month late, plus interest. Some states assess a separate late-filing penalty even if you owe nothing.
Automate where you can. Tools like Avalara, TaxJar, or Vertex connect directly to your sales channels, calculate liability by jurisdiction, and generate return-ready reports. These tools cost money, but the cost is almost always lower than a single audit adjustment. For sellers with nexus in fewer than five states, manual filing is still workable — but build a calendar with every due date and set reminders 10 days in advance.
When you file, reconcile your platform’s reported gross sales against your actual remittance. Discrepancies are the first thing auditors look for. Document every exemption you claim — resale certificates, nonprofit exemptions, direct pay permits — and store them for at least five years.
Common Mistakes to Avoid
The most expensive mistake is assuming marketplace sales fully cover your registration and filing obligations — they don’t in most states. A close second is treating economic nexus thresholds as permanent: thresholds can change with state legislation, and a state where you were safely under $100,000 last year might now have a $50,000 threshold. Third, many sellers configure their platform tax settings once and never revisit them, leaving outdated product tax codes and sourcing rules in place as laws evolve. Finally, international sellers frequently ignore U.S. state obligations entirely until a marketplace enforces compliance on their behalf — by which point back periods have already accumulated. Review your nexus footprint, your product taxability assignments, and your filing calendar at least once per year. Sales tax is not a one-time setup; it’s an ongoing operational function.
