Sales Tax Nexus for E-Commerce Sellers: What Triggers It, Which States Matter, and the Best Software to Handle It

If you sell products online and ship to customers in multiple states, you almost certainly owe sales tax in more places than you are currently collecting it. Most e-commerce sellers know this in the abstract but have not done anything about it — either because the rules seem impossibly complex, or because they are hoping the problem will stay small enough to ignore.

It will not stay small. States have become significantly more aggressive about enforcement since the Supreme Court's 2018 decision in South Dakota v. Wayfair, and the tools they use to identify non-compliant sellers have gotten sharper. The good news is that the software solutions have gotten sharper too — and for most e-commerce businesses, the compliance burden is genuinely manageable if you set things up correctly.

This article explains how nexus works, which states create the most exposure, and how to evaluate the three software platforms that dominate the space.

Nexus is the legal connection between your business and a state that gives that state the right to require you to collect and remit sales tax. Before Wayfair, nexus required a physical presence in a state — a warehouse, an office, an employee, or inventory stored at a fulfillment center. If you had no physical footprint in a state, that state could not require you to collect sales tax from its residents.

Wayfair changed that. The Supreme Court upheld South Dakota's economic nexus law, which imposed sales tax collection obligations on sellers who exceeded $100,000 in sales or 200 transactions into the state — regardless of whether they had any physical presence there. Within two years, every state with a sales tax had enacted its own economic nexus law.

Today, nexus can be triggered by:

• Economic nexus — exceeding a state's sales or transaction threshold (the most common trigger for e-commerce sellers)
• Physical nexus — having a warehouse, office, employee, or contractor in the state
• Inventory nexus — storing inventory in a third-party fulfillment center (Amazon FBA sellers take note: every state where Amazon stores your inventory is a nexus state)
• Click-through nexus — having affiliates or referral partners in a state that drive sales to your site
• Marketplace facilitator rules — if you sell through Amazon, Etsy, eBay, or Walmart Marketplace, the marketplace collects and remits sales tax on your behalf in most states; your own direct sales are still your responsibility

Most states use $100,000 in sales or 200 transactions as their threshold, but there are important variations:

Key point: Thresholds are typically measured on a rolling 12-month basis, not a calendar year. If you exceed a threshold in October, you may owe sales tax on sales made in November and December of that year — not just starting January 1.

Five states have no sales tax at all: Alaska, Delaware, Montana, New Hampshire, and Oregon. Sales into these states are never subject to state sales tax (though Alaska allows local jurisdictions to impose their own taxes, and some do).

If you sell through Amazon's Fulfilled by Amazon (FBA) program, Amazon stores your inventory in fulfillment centers across the country. You typically have no control over which warehouses hold your products. This creates physical nexus in every state where Amazon stores your inventory — which can easily be 20 or more states.

This is one of the most common sources of unexpected sales tax exposure for e-commerce sellers. You may have never set foot in Ohio, but if Amazon stores your products in their Etna, Ohio fulfillment center, you have physical nexus in Ohio and owe sales tax on every sale shipped to an Ohio customer — even if you are well below Ohio's economic nexus threshold.

Amazon provides a report called the Inventory Event Detail report that shows which states have held your inventory. If you are an FBA seller and have never reviewed this report, you should do so immediately.

Once you have nexus in a state, you need to know which tax rate to charge. Most states use destination sourcing — you charge the tax rate of the buyer's location (their city, county, and state). A handful of states use origin sourcing — you charge the tax rate of your business location.

Origin-sourcing states include Arizona, Illinois, Mississippi, Missouri, New Mexico, Ohio, Pennsylvania, Tennessee, Texas, Utah, and Virginia (with some nuances). In these states, you charge your home rate regardless of where the buyer is located.

This matters because destination sourcing requires you to know the correct combined rate for thousands of zip codes and jurisdictions. That is not something you can manage manually — it is exactly what the software platforms are built to handle.

There are dozens of sales tax software tools on the market, but three dominate the e-commerce space. Here is an honest assessment of each.

Best for: Mid-market and enterprise sellers with complex multi-channel operations, international sales, or high transaction volumes.

Avalara is the most comprehensive platform in the market. It handles sales tax calculation, filing, remittance, exemption certificate management, and cross-border VAT/GST for international sales. It integrates with virtually every major e-commerce platform, ERP, and accounting system.

Strengths:

• Deepest integration library (Shopify, WooCommerce, Magento, BigCommerce, NetSuite, QuickBooks, Salesforce, and hundreds more)
• Handles product taxability rules — not every product is taxable in every state, and Avalara's product classification engine is the most sophisticated available
• Manages exemption certificates (resellers, nonprofits, government buyers) with automated collection and storage
• International VAT/GST compliance for sellers shipping to the EU, UK, Canada, and Australia
• Dedicated compliance team for back-filing and voluntary disclosure agreements

Weaknesses:

• Pricing is opaque and negotiated — expect to pay $500–$2,000+ per month depending on transaction volume and features
• Implementation requires professional setup; it is not a plug-and-play tool
• Customer support quality has been inconsistent as the company has grown

Who should use it: Sellers doing $1M+ in annual revenue across multiple channels, sellers with international sales, or any business with complex product taxability questions (food, clothing, software, medical devices).

Best for: Small to mid-size e-commerce sellers who want accurate calculations and automated filing without enterprise complexity.

TaxJar was acquired by Stripe in 2021 and has been integrated into the Stripe ecosystem, though it continues to operate as a standalone product. It is the most user-friendly of the three platforms and is particularly well-suited for sellers who want to get compliant without hiring a dedicated tax team.

Strengths:

• Clean, intuitive interface — the easiest of the three to set up and use
• AutoFile feature handles filing and remittance in all states where you are registered, automatically
• Strong Shopify, WooCommerce, Amazon, and Etsy integrations
• Transparent, volume-based pricing starting around $19/month for low-volume sellers
• Excellent nexus tracking dashboard that shows where you are approaching thresholds
• Stripe integration means seamless connection if you use Stripe as your payment processor

Weaknesses:

• Less sophisticated product taxability engine than Avalara — may require manual overrides for complex product categories
• Limited international VAT/GST support
• Exemption certificate management is basic compared to Avalara
• Not ideal for businesses with ERP systems or complex multi-entity structures

Who should use it: Shopify, WooCommerce, or Amazon sellers doing under $5M in annual revenue who want automated filing and a clean dashboard without enterprise pricing.

Best for: Sellers whose entire operation runs through Shopify and who want zero-friction compliance built into their existing platform.

Shopify Tax is Shopify's native sales tax solution, launched in 2022 and significantly expanded since. It is not a standalone product — it only works within the Shopify ecosystem — but for sellers who live in Shopify, it is the most frictionless option available.

Strengths:

• Built directly into Shopify — no third-party integration required
• Automatically calculates the correct rate at checkout based on the buyer's location
• Nexus tracking built into the dashboard — Shopify alerts you when you are approaching thresholds in new states
• No additional monthly fee for basic tax calculation (included with Shopify subscription)
• Handles marketplace facilitator rules automatically for Shopify Markets

Weaknesses:

• Only works for sales made through Shopify — if you also sell on Amazon, Etsy, your own WooCommerce site, or wholesale, you need a separate solution for those channels
• Filing and remittance are not automated — you still need to log into each state's portal and file manually, or use a third-party service
• Product taxability rules are less granular than Avalara or TaxJar
• No exemption certificate management

Who should use it: Shopify-only sellers who want accurate rate calculation without paying for a separate platform, and who are comfortable handling their own filing or working with an accountant to do so.

The right platform depends on three factors: where you sell, how you sell, and how much you sell.

If you sell exclusively through Shopify and your volume is manageable, start with Shopify Tax for calculation and work with your accountant for filing. It is free and accurate.

If you sell through multiple channels (your own site plus Amazon, Etsy, or wholesale), TaxJar is the most practical choice for most small to mid-size sellers. The AutoFile feature alone is worth the subscription cost — manually filing in 20+ states every month is a significant time burden.

If you are doing significant volume, have complex product categories, sell internationally, or manage exemption certificates, Avalara is the right tool. The higher cost is justified by the depth of the platform and the reduction in compliance risk.

If you have been selling online for more than a year or two without collecting sales tax in states where you have nexus, you have a back-filing problem. This is more common than most sellers realize, and it is not something to ignore.

Most states offer Voluntary Disclosure Agreements (VDAs) that allow sellers to come forward, pay back taxes for a limited lookback period (typically two to four years), and receive a waiver of penalties. This is almost always a better outcome than waiting for a state to find you through an audit.

The Multistate Tax Commission (MTC) runs a National Nexus Program that allows sellers to apply for VDAs in multiple states simultaneously through a single application. This is the most efficient path for sellers with exposure in many states.

If you have back-filing exposure, the sequence is:

1. Determine which states you have nexus in and for how long
2. Quantify the approximate tax owed in each state
3. Evaluate whether VDA is available and appropriate in each state
4. Register, back-file, and remit
5. Implement ongoing compliance software going forward

This is not a DIY project. The analysis requires someone who understands both the nexus rules and the VDA process in each state.

Consider a seller who launched a Shopify store in 2023 selling handmade leather goods. By mid-2024, they were shipping to customers in 35 states. They had nexus in California (FBA inventory), Texas (economic nexus), Florida (economic nexus), and a dozen other states — but were only collecting sales tax in their home state of Arizona.

By the time they came to us in early 2026, they had approximately $180,000 in uncollected sales tax across 14 states, plus potential penalties. Through the MTC's National Nexus Program, we were able to resolve the back-filing in 11 of those states with a two-year lookback and full penalty abatement. The actual tax owed was approximately $62,000 — painful, but far less than the full exposure with penalties would have been.

Going forward, they implemented TaxJar with AutoFile enabled in all 14 states. Their monthly compliance cost is now $89/month and requires no manual intervention.

Sales tax compliance for e-commerce sellers is genuinely complex — but it is not optional, and it is not getting simpler. The states have the data, the tools, and the motivation to find non-compliant sellers. The question is whether you address the exposure proactively or reactively.

The software platforms available today make ongoing compliance manageable for businesses of almost any size. The harder problem is usually the back-filing — figuring out where you have been non-compliant and resolving it before a state finds you first.

If you are an e-commerce seller who has not done a formal nexus analysis, that is the right place to start. The analysis will tell you which states you owe, how much exposure you have, and what the most cost-effective path to compliance looks like.

Send us an inquiry — we work with e-commerce sellers at every stage, from initial nexus analysis through back-filing resolution and ongoing compliance strategy.