Selling online creates state tax obligations that most sellers discover only when they receive a notice from a state revenue department. The combination of Wayfair economic nexus (triggered by sales volume alone) and FBA physical nexus (triggered by Amazon storing inventory in a state's warehouses) means a typical Amazon FBA seller has nexus in 20-30 states - many of which they have never visited. Understanding which taxes apply, who collects them, and what income must be reported where is the minimum viable tax knowledge for any e-commerce business.
Economic nexus (post-Wayfair): Selling more than $100,000 or making 200+ transactions into a state creates sales tax nexus in that state - even with no physical presence. This applies to all 45 states with sales tax. A seller based in Texas who makes $150,000 in sales to Florida customers has Florida nexus and must collect Florida sales tax.
Physical nexus via FBA inventory: Amazon FBA (Fulfillment by Amazon) stores seller inventory in Amazon fulfillment centers across the country. When Amazon stores your inventory in a state, you have physical nexus in that state for both sales tax AND state income tax purposes - regardless of your sales volume there. Amazon publishes a list of fulfillment center states but does not control which states receive your inventory.
In 45+ states, marketplace facilitators - Amazon, eBay, Etsy, Walmart Marketplace, and similar platforms - are required to collect and remit sales tax on behalf of third-party sellers. This means: if you sell on Amazon in a state where Amazon is registered as a marketplace facilitator, Amazon collects the sales tax from your customer and remits it to the state. You do not collect or remit sales tax on those transactions. This eliminates most of the sales tax collection burden for marketplace sellers - but it does not eliminate the income tax nexus created by physical inventory presence.
When your inventory is stored in an Amazon fulfillment center in a state, you have physical presence - nexus - in that state for income tax purposes. Most states require businesses with nexus to file a state income tax return and pay tax on income apportioned to that state. For an e-commerce seller, income is typically apportioned using a single-factor sales formula - the ratio of that state's sales to total sales. A seller with $500,000 total revenue who makes $50,000 (10%) of sales to customers in a state where Amazon stores inventory allocates 10% of net income to that state and owes state income tax on that amount.
Many states provide a de minimis threshold below which income tax filing is not required. California requires registration if you have any California property, while other states have minimum thresholds of $50,000 or $100,000 of in-state sales before income tax filing is required. Amazon's Seller Central account can provide a state-by-state inventory report showing which states stored your products during the year.
An individual running an e-commerce business reports income on Schedule C. Net profit is subject to self-employment tax at 15.3% on the first $184,500 (2026 SE wage base) and 2.9% above that - in addition to regular income tax. The SE tax deduction (one-half of SE tax) reduces AGI. Key deductible expenses for online sellers: cost of goods sold, Amazon/platform fees, shipping costs, packaging materials, advertising and marketing, software subscriptions (inventory management, accounting), home office if dedicated space is used exclusively for the business, and a portion of internet and phone costs.
Sellers with significant inventory must choose an inventory accounting method that affects both their COGS calculation and their taxable income. Under the uniform capitalization rules (§263A), larger sellers must capitalize certain indirect costs into inventory. Smaller sellers (gross receipts under $30 million) can use the simplified cash method for inventory or a non-AFS inventory method. The choice between FIFO (first in, first out) and specific identification affects which inventory costs are expensed and when - in an inflationary environment, specific identification of lower-cost batches can reduce COGS and increase taxable income, while identifying higher-cost units reduces taxable income.