Sales Tax for Online Sellers: Complete Ecommerce Tax Guide

Sales Tax Nexus: Where You Owe Tax

Sales tax nexus is the connection between your business and a state that creates a sales tax collection obligation. Before the Wayfair decision, nexus was almost exclusively based on physical presence: a warehouse, an office, an employee, or inventory stored in a state. If you had no physical footprint in a state, you generally did not need to collect sales tax on sales to customers there. That framework made sense when most commerce happened in brick-and-mortar stores, but it created a competitive advantage for online sellers who could sell to customers in 45 states without collecting sales tax in most of them.

Physical nexus still exists and still matters. If you store inventory in an Amazon FBA warehouse in Texas, you have physical nexus in Texas. If you attend a trade show in California and make sales, you may trigger temporary nexus in California. If you hire a remote employee in Georgia, you have nexus in Georgia. Physical nexus thresholds are typically zero, meaning any physical presence of any duration creates a collection obligation. Our guide to sales tax nexus covers every type of nexus trigger and how each one applies to online sellers.

The 45 states that impose a general sales tax (all states except Alaska, Delaware, Montana, New Hampshire, and Oregon) each set their own nexus rules, tax rates, product taxability rules, filing frequencies, and deadlines. Alaska has no state sales tax but allows some local jurisdictions to impose their own sales taxes, creating a unique compliance situation for sellers shipping there. This state-by-state variation is what makes sales tax compliance complex for online sellers: you are not dealing with one tax system, you are dealing with up to 45 separate systems, each with its own rules and requirements.

Sales tax rates vary dramatically by location. State rates range from 2.9% in Colorado to 7.25% in California, but most jurisdictions add county and city taxes on top of the state rate. Combined state and local rates in some parts of Louisiana, Tennessee, and Arkansas exceed 10%. A single state can have hundreds of different combined rates depending on the customer's exact address, which is why accurate rate calculation requires software rather than manual lookup. Our origin vs destination tax guide explains the two systems states use for determining which rate applies to a transaction.

The Wayfair Decision and Economic Nexus

South Dakota v. Wayfair, decided by the US Supreme Court on June 21, 2018, overturned the physical presence standard from the 1992 Quill v. North Dakota decision and ruled that states can require out-of-state sellers to collect sales tax based on their economic activity in the state. This decision created what is now called economic nexus, and within three years of the ruling, all 45 sales tax states plus the District of Columbia had enacted economic nexus laws.

The most common economic nexus threshold is $100,000 in sales or 200 transactions in a state within the current or prior calendar year. South Dakota's law used this threshold, and most states adopted the same numbers. However, several states have set different thresholds. California set its threshold at $500,000 in sales with no transaction count test. Texas uses $500,000 in sales. New York uses $500,000 in sales and 100 transactions (both conditions must be met). Some states have eliminated the transaction count threshold entirely, keeping only the dollar amount test. These thresholds change periodically, so checking current thresholds when evaluating your nexus exposure is essential.

Economic nexus is measured on a rolling basis, and the measurement period varies by state. Most states look at the current calendar year or the prior calendar year, meaning if you crossed the threshold at any point in either year, you have nexus. Once you trigger economic nexus, the obligation typically begins on the first transaction after you cross the threshold or on the first day of the next month, depending on the state. Some states, like Pennsylvania and Oklahoma, start the obligation retroactively to the beginning of the calendar year in which you crossed the threshold, which creates a back-filing requirement for the months between January and when you actually crossed the threshold.

For most online sellers doing under $1 million in total annual revenue, economic nexus creates obligations in a handful of states where they have concentrated customers. A seller doing $500,000 per year might only cross the $100,000 threshold in 2 to 5 states, plus any states where they have physical nexus. As your revenue grows, so does the number of states where you have nexus. A seller doing $5 million per year likely has economic nexus in 20 or more states and needs comprehensive multi-state compliance.

Collecting Sales Tax on Your Store

Before you can legally collect sales tax, you must register for a sales tax permit in each state where you have nexus. Collecting sales tax without a permit is illegal in every state. Registration is free in most states and done through the state's department of revenue website. Many states also participate in the Streamlined Sales Tax Registration System (SSTRS), which lets you register in 24 member states through a single online application at sstregister.org. For non-member states (including California, Texas, New York, and Florida, which are among the largest), you must register individually through each state's portal.

Once registered, you need to configure your online store to calculate and collect the correct tax amount on every taxable transaction. Every major ecommerce platform, including Shopify, WooCommerce, BigCommerce, and Squarespace, has built-in sales tax calculation or integrates with tax calculation services. The key configuration decisions are which states to collect in (everywhere you have nexus), whether to use the platform's built-in calculations or a third-party service like TaxJar or Avalara for better accuracy, and how to handle tax on shipping charges (which is taxable in some states and exempt in others).

Accuracy in tax calculation matters because both overcollecting and undercollecting create problems. If you collect too much tax from customers, you owe the excess to the state and may face penalties for overcollection. If you collect too little, you owe the difference out of your own pocket when you file your return. For businesses selling in 5 or more states, manual rate management is impractical, and automated tax calculation software pays for itself by avoiding errors. Our sales tax software comparison covers the options at every price point.

Not every product you sell is taxable in every state. Clothing is exempt in Pennsylvania, New Jersey, and Minnesota but taxable in most other states. Food and groceries have varying exemptions. Digital products are taxed in some states and exempt in others, with many states still clarifying their positions on digital goods. Product taxability is one of the most complex areas of sales tax compliance, and getting it wrong means either overcharging customers or underpaying the state.

Filing Returns and Staying Compliant

Every state where you hold a sales tax permit requires you to file periodic sales tax returns, even in periods where you made no sales and collected no tax. Filing frequency is assigned by the state, typically based on your sales volume: monthly for sellers collecting over $300 to $1,000 per month in tax, quarterly for moderate-volume sellers, and annually for low-volume sellers. Missing a filing deadline results in late filing penalties and interest charges in every state, which accumulate even if the return shows zero tax due.

A sales tax return reports your total sales in the state, your taxable sales, any exempt sales (with exemption categories), the tax collected, and the tax due. Some states break this down by county or local jurisdiction, which means a single state return might require you to allocate sales across dozens of local tax districts. This jurisdictional breakdown is where manual filing becomes prohibitively time-consuming and error-prone, and where sales tax automation software provides the most value.

Many states offer a vendor discount, also called a timely filing discount, which lets you keep a small percentage of the tax you collect if you file and pay on time. The discount ranges from 0.5% to 5% depending on the state, often with a cap. In a state like Ohio, the vendor discount is 0.75% of the tax collected. In Texas, it is 0.5% with a $10,000 cap per reporting period. These discounts are small but add up for high-volume sellers, and they reward consistent, timely compliance. Multi-state compliance requires tracking different filing frequencies, deadlines, and filing methods across every state where you are registered.

Our sales tax filing deadlines calendar provides the specific due dates for every state by filing frequency, so you never miss a deadline and trigger unnecessary penalties.

Sales Tax Software and Automation

Sales tax software handles the three core functions of sales tax compliance: calculating the correct tax on each transaction in real time, preparing and populating sales tax returns with your transaction data, and in many cases, automatically filing those returns and remitting payment on your behalf. The cost of sales tax software ranges from free (for basic Shopify and WooCommerce integrations) to $50 to $500+ per month for full-service solutions, depending on transaction volume and the number of state filings.

TaxJar and Avalara are the two dominant sales tax automation platforms for ecommerce businesses. TaxJar, now owned by Stripe, starts at $19 per month for basic sales tax calculations and offers AutoFile (automated return filing) as an add-on at $24.99 per state per month. Avalara offers a broader feature set with more granular product taxability classifications and enterprise-grade capabilities, but pricing starts higher and is quote-based for most plans. Both integrate directly with Shopify, WooCommerce, BigCommerce, Amazon, Etsy, eBay, and most other selling platforms.

For sellers on Shopify specifically, Shopify's built-in tax engine provides basic sales tax calculation at no additional cost using Shopify Tax, which covers destination-based rate lookups and product category-based taxability for US transactions. Shopify Tax handles calculation but does not file returns, so you either file manually or connect a filing service. For sellers in fewer than 5 states with straightforward product taxability, Shopify's built-in system may be sufficient. For sellers in more states or with products that have complex taxability rules (like food, clothing, or digital goods), a dedicated solution provides better accuracy.

Special Situations and Product Types

Marketplace facilitator laws in all 45 sales tax states plus DC require marketplaces like Amazon, Etsy, eBay, and Walmart to collect and remit sales tax on behalf of third-party sellers for orders placed through the marketplace. This means if you sell on Amazon, Amazon handles sales tax collection and remittance for those orders in every state. You do not need to separately collect or remit tax on marketplace sales. However, you still need to track marketplace sales for nexus calculation purposes (in most states, marketplace sales count toward your economic nexus threshold for direct sales), and you still need to file returns that include marketplace data in some states.

Dropshipping sales tax involves a three-party transaction where the seller, the supplier, and the customer are often in different states. The sales tax obligation falls on the seller (you) based on the customer's location, not the supplier's location. If you dropship to a customer in Texas and you have nexus in Texas, you collect Texas sales tax at the customer's local rate, regardless of where the supplier ships from. The supplier typically does not charge you sales tax if you provide a resale certificate proving you are purchasing for resale rather than personal use.

International sellers and VAT introduces a different tax framework entirely. If you sell to customers in the European Union, the UK, Canada, or Australia, you may have value-added tax (VAT) or goods and services tax (GST) obligations in those countries. The EU's Import One-Stop Shop (IOSS) system, implemented in July 2021, simplifies VAT collection for non-EU sellers on shipments valued under 150 euros. Understanding when and how to register for VAT is increasingly important as ecommerce becomes more global.

If you have been selling without collecting sales tax in states where you had nexus, you likely owe back taxes, penalties, and interest. Most states offer voluntary disclosure agreements (VDAs) that limit your lookback period (typically 3 to 4 years instead of the full statute of limitations), waive or reduce penalties, and allow you to come into compliance without the adversarial dynamic of an audit. A VDA is almost always preferable to waiting for the state to discover your non-compliance through a sales tax audit.

Understanding Nexus and Tax Rules

Collecting and Filing Guides

Sales Tax Software and Platform Setup

Platform-Specific Tax Guides

Product Taxability and Exemptions

Audits, Penalties, and International