Last Updated: June 27, 2026
Forty-five states, the District of Columbia, and thousands of local municipalities collect sales tax. The average combined rate sits around 7%, but in places like parts of California or Illinois, it clears 10%. For an online business scaling across state lines, that math gets complicated fast, and the penalties for getting it wrong can run 25% of tax due plus interest before you even know there’s a problem.
Sales tax used to be simpler. Before 2018, you only owed it where you had a physical presence. Then the Supreme Court’s South Dakota v. Wayfair decision blew that up. Now, selling enough into a state is sufficient to trigger an obligation, regardless of where you’re located. If you run an online business and you’re not tracking this, you’re probably already exposed.
Nexus: The Word That Determines What You Owe
Nexus is your legal connection to a state that requires you to collect and remit sales tax there. It comes in two flavors: physical and economic.
Physical nexus is what most people think of: an office, warehouse, employees, or inventory stored in a state. That last one catches Amazon FBA sellers off guard regularly. If Amazon stores your products in a fulfillment center in Pennsylvania, you have nexus in Pennsylvania, even if you’ve never set foot there.
Economic nexus is the post-Wayfair reality. Every sales-tax state now has economic nexus rules based purely on sales volume. Most states set the threshold at $100,000 in gross sales or 200 transactions in a calendar year. California, New York, and Texas use a $500,000 threshold. Cross those lines and you’re on the hook, registration required, filings due.
Affiliate and click-through nexus can also apply if you pay commissions to in-state influencers or referral partners, sometimes at thresholds as low as $10,000. The practical fix: export your sales by ship-to state every month and track where you’re approaching thresholds. Automation tools do this automatically.
What Actually Gets Taxed
Physical products are almost always taxable, with carve-outs for things like groceries in many states and clothing during tax holidays. Where it gets genuinely complicated is digital goods and services.
Downloaded software, e-books, and SaaS products are taxable in an expanding list of states. Professional services like accounting and legal work are frequently exempt, but hosted software, digital marketing tools, and subscriptions often are not. The rules vary by state and change regularly.
Shipping and handling is taxable in most destination states if the seller arranges delivery. Exemptions exist for resale certificates, nonprofits, and government purchasers. If you sell B2B, collect valid resale certificates at checkout and track their expirations.
One important mechanic worth understanding: most states use destination-based sourcing, meaning tax is calculated where the buyer receives the goods. A handful use origin-based sourcing (taxed at the seller’s location). For multi-state sellers, the difference matters for rate calculations.
How the Money Actually Flows
The operational loop is the same regardless of what you sell or where. A customer enters a shipping address, your system applies the applicable state and local rates (there are 11,000+ local rate combinations in the U.S.), taxability rules are applied based on your product type, tax is added to the total, the customer pays, and you hold those funds until the filing deadline for that jurisdiction.
Filing frequency depends on volume: monthly, quarterly, or annual. Most states require filing even when you owe zero, so-called zero returns. Miss a filing and you’re looking at penalties even if your tax liability was nothing.
Registration comes first. Once you hit a nexus threshold, you register for a seller’s permit through the state’s online portal, usually free or under $100. Some states require immediate collection once registered; others give a short grace period. This is not something to procrastinate on.
Platform-Specific Realities: Shopify, Stripe, and Amazon
Shopify includes Shopify Tax built into the platform, which handles real-time rate calculations, nexus monitoring, and exemption management across U.S. jurisdictions. For full managed filing and registration, you’ll want to pair it with a dedicated service like Zamp or Avalara via their app integrations.
Stripe Tax is one of the cleanest setups if you already run payments through Stripe. It identifies nexus automatically, handles registrations through partners, and covers global VAT and GST for international sales. Pricing is usage-based with filing fees on top. TaxJar, which Stripe acquired, remains a strong standalone option particularly for e-commerce.
Amazon is a marketplace facilitator in virtually every state, which means Amazon collects, remits, and handles refunds on third-party sales through its platform. The catch: FBA inventory creates physical nexus everywhere Amazon warehouses your products, and Amazon’s facilitator role covers only sales made through Amazon. Direct sales on your own site in those states are your responsibility.
Multi-channel sellers need to reconcile reports across all platforms. This is where dedicated automation tools earn their keep.
The Tools: Zamp, Avalara, Stripe Tax, and the Rest
Zamp is the service I use for our U.S. operations and the one I’d recommend to most growing online businesses. It’s a fully managed service: nexus tracking, registrations, calculations, filings, remittances, and exemption management, all handled for you. Integrations cover Shopify, Amazon, BigCommerce, QuickBooks, and others, plus a clean API. The pricing is flat monthly, no per-transaction surprises. What actually differentiates Zamp from software-only solutions is support. Their team handles registrations without pushing the work back onto you, which was the thing that finally drove me away from Avalara.
Avalara is the right choice for complex, high-volume, or enterprise-level operations. Its calculation engine handles hundreds of product categories, international VAT and GST, and custom taxability rules. The exemption certificate management system (CertCapture) is best-in-class for B2B sellers with heavy certificate volume. For growing businesses that don’t need that complexity, it’s often more than necessary.
Stripe Tax and TaxJar are excellent for subscription businesses and pure e-commerce sellers already on Stripe. Global coverage, automatic nexus detection, and AutoFile for returns make it a clean one-stop option.
Other options worth knowing: TaxCloud is free or low-cost and solid for basic calculation needs. Kintsugi and Numeral are newer entrants with strong SaaS-specific workflows. Vertex and Sovos operate at the enterprise tier for very large operations.
A Note on Canada
Zamp handles U.S. operations beautifully but does not currently offer Canadian sales tax services. For Canadian compliance, we use Hands Off Sales Tax (HOST), which we found through the Stripe app. If you sell products or services in Canada and process payments through Stripe, HOST is a natural fit for handling Canadian sales tax filing, reporting, and API integration.
In our business we made the strategic decision not to sell products in Canada due to the administrative complexity. You must calculate federal sales tax, provincial taxes and convert to $CAD on your site. You also need to work with your delivery partner on import duties. Needless to say it’s a complex process and we determined the juice wasn’t worth the squeeze in Canada.
Sales Tax Nexus Can Trigger Income Tax Obligations Too
This is the part most founders miss. Creating sales tax nexus in a state does not automatically create income tax nexus, but the two often travel together, particularly for service and digital businesses.
Sales tax nexus governs your collection and remittance obligations. Income tax nexus determines whether a state can tax your business profits. Many states apply broader economic standards, meaning significant in-state sales can trigger income tax filing requirements even without any physical presence.
Sellers of physical goods get some protection from Federal P.L. 86-272, which shields businesses from state net income tax when the only in-state activity is soliciting orders fulfilled from out of state. That protection does not apply to services, SaaS, or digital products.
The practical guidance: if you’re hitting sales tax thresholds in a state, check your income tax exposure at the same time. A CPA who understands multi-state compliance is worth the conversation before the obligations pile up.
Our Experience Scaling Compliance
We process 50 to 100 transactions per day and sell products across all 50 states plus Canada. Three years ago, our only nexus obligation was California. Since then, we’ve entered nexus in 17 additional states and expect to add another 10 to 15 this year.
Early on, tracking sales manually and remitting through the California CDTFA portal was manageable. When we crossed into a second state, it was still workable. A few hours a month. Stripe and Avalara’s base software handled the volume.
The wheels came off as we scaled. What had been a few hours monthly turned into a full day of my week: reconciling filings, tracking new jurisdictions, keeping records clean. I upgraded to Avalara’s full-service program thinking it would solve the problem, but every new state registration turned into a handoff problem where Avalara pushed the burden back onto me. For a founder running multiple functions, that’s not sustainable.
After a lot of research and some frustrating calls, I switched to Zamp. One demo was enough. Their API connected both our Stripe and TrueMed payment flows cleanly, the dashboard is more intuitive than Avalara, and the support is genuinely responsive. At every stage of onboarding, adding new state registrations, and API troubleshooting, their team has been competent and fast. That combination is rarer than it should be.
If sales tax compliance is consuming time you should be spending on growth, a full-service solution is the right call. Zamp is the one I’d point you to.
How to Get Your Compliance in Order
The starting point is a sales report export: last 12 months, sorted by ship-to state. That tells you exactly where you have nexus obligations today. Register in any state where you’ve crossed the threshold, or explore a Voluntary Disclosure Agreement if you’re behind; most states offer penalty relief through VDA programs for businesses that self-report.
Enable Shopify Tax or Stripe Tax if you’re not already using platform-level calculation. Evaluate a full-service provider if you’re operating in more than a few states. Separate collected sales tax into its own account and treat it as a liability from day one. Schedule a 30-minute call with a CPA who knows e-commerce before the end of the quarter.
Sales tax compliance is not the interesting part of building a company. Automate it early, keep it organized, and get back to the work that actually moves the needle.