Sales Tax for E-Commerce Businesses Selling Across State Lines

Sales tax for e-commerce businesses depends on where your customers are located and whether you have nexus — a legal connection — in their state. Once you cross a state's nexus threshold, you're required to register, collect, and remit sales tax there. This guide explains how nexus works, how to figure out your obligations, and how to stay compliant.

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. For e-commerce businesses, nexus can exist in multiple states at once — and you may not realize it until you're already over a threshold.

5 states have no statewide sales tax: Alaska, Delaware, Montana, New Hampshire, and Oregon. Alaska allows local jurisdictions to impose their own taxes, but the other 4 do not. Every other state — plus Washington D.C. — imposes sales tax on transactions within its jurisdiction. That means if you sell into 45 states, you potentially have 45 sets of rules to track.

Most e-commerce businesses don't start with nexus everywhere. You build it over time as your sales grow — which is why tracking your sales by state from the beginning is worth the effort.

There are 2 main ways your business can establish nexus in a state: physical presence and economic activity. Understanding both matters because either one can trigger a collection obligation — even if you've never set foot in the state.

Physical nexus

Physical nexus is created when your business has a tangible presence in a state. This includes owning or leasing property, having employees or contractors working there, or storing inventory in a warehouse or fulfillment center in that state.

For e-commerce sellers using third-party fulfillment services — including Amazon FBA — storing inventory in a fulfillment center typically creates physical nexus in that state, even if you never chose to operate there. That's a detail that catches a lot of online sellers off guard.

• Office, store, or other physical facility in the state
• Employees or independent contractors working in the state
• Inventory stored in a warehouse or fulfillment center in the state
• Temporary sales activity like trade shows or pop-up booths

Economic nexus

Economic nexus doesn't require any physical presence. After the U.S. Supreme Court's South Dakota v. Wayfair decision, states can require out-of-state sellers to collect and remit sales tax based on sales volume alone.

Most states use a threshold of $100,000 in sales into the state, a 200-transaction count, or both. Thresholds vary — some states require you to hit both the dollar amount and the transaction count before economic nexus applies. You need to track your sales into each state separately against that state's specific threshold.

Once you know you have nexus in a state, you need to figure out which tax rate to charge. That depends on the state's sourcing rules — whether the state taxes based on where you (the seller) are located or where the customer receives the order.

Origin-based sourcing

In an origin-based state, you charge the tax rate for your business's location — the ship-from address — and remit that tax to your home state. A smaller number of states use this approach.

Destination-based sourcing

Most states use destination-based sourcing. You charge the tax rate for the customer's delivery address and remit that tax to the customer's state. For e-commerce businesses shipping to customers across the country, this is the more common scenario — and the more complex one, since local rates within a state can vary.

Once you have nexus in a state, there are 3 things you need to do: register for a sales tax permit, collect the correct amount from customers, and file returns with remittance on the state's schedule. Skipping any of these steps can leave you on the hook for back taxes and penalties.

Register before you collect

You need to apply for a sales tax permit — sometimes called a seller's permit — in each state where you have nexus before you start collecting tax from customers there. Most states handle registration through their department of revenue website. The Streamlined Sales Tax Governing Board offers a single registration system that covers 24 member states, which can reduce the paperwork if you're registering in multiple states at once.

Collect the right amount

For most remote sales, you'll use the customer's ship-to address to determine the applicable rate. Rates can include state, county, city, and special district components — so the rate for one ZIP code can differ from the rate in the next one. Manual rate lookups are error-prone at scale. Most e-commerce platforms integrate with tax calculation tools that handle this automatically at checkout.

File and remit on time

Each state sets its own filing frequency — monthly, quarterly, or annually — usually based on your sales volume in that state. You'll file a return and remit the tax you collected during that period. Missing a deadline can mean interest and penalties, so tracking due dates across multiple states is one of the harder parts of multi-state compliance.

If you buy goods to resell, you generally don't pay sales tax on those purchases — you collect it from your end customer instead. A resale certificate is the document that makes this work. You provide it to your supplier to document the tax-free purchase, and the tax obligation shifts to the final sale.

Resale certificates are tied to your sales tax registration in each state. Most states issue their own certificate form, but many also accept standardized multistate forms — including the Multistate Tax Commission's Uniform Sales and Use Tax Resale Certificate and the Streamlined Sales Tax Exemption Certificate — subject to each state's specific instructions.

Not every state accepts out-of-state resale certificates, so check the rules for each state where you're purchasing inventory. A tax professional can help you figure out which certificates are valid where.

If you run an affiliate program, you may have nexus in states where your affiliates are located — even if you have no physical presence there and haven't crossed an economic nexus threshold. This is called affiliate nexus, and it's one of the less obvious ways e-commerce businesses end up with collection obligations.

Affiliate nexus rules vary by state. Some states trigger it based on a commission-based referral relationship. Others use sales or transaction thresholds tied to affiliate-driven activity. A common trigger is an in-state blogger, influencer, or promoter directing customers to your store through tracked links.

No 2 states' affiliate nexus laws are exactly alike, so if you run any kind of referral or affiliate program, it's worth reviewing your exposure state by state.

Managing sales tax across multiple states manually is where most e-commerce businesses run into trouble. Sales tax automation tools handle 2 distinct jobs: calculating the correct tax on each order at checkout, and preparing returns and remittance reports for each state where you file.

A tax calculation engine pulls current rate data and applies the right rate based on the customer's delivery address, reducing the risk of charging the wrong amount. A filing tool pulls your sales data across channels and generates the jurisdiction-specific reports you need to file and remit.

These tools don't replace a tax professional — especially if you're unsure whether you have nexus in a state or how to handle a specific product exemption. But for the mechanical work of calculating and filing, automation reduces missed deadlines and manual errors at scale.