Tax Planning for E-Commerce Businesses: Amazon FBA, Multi-State Sales Tax Nexus, and Inventory Accounting

E-commerce taxation has become dramatically more complex since the Supreme Court’s Wayfair decision eliminated the physical presence requirement for sales tax collection. Under the economic nexus framework, an online seller who ships products to customers in a state is required to collect and remit sales tax once they exceed that state’s threshold (such as $100,000 of sales in Florida or Pennsylvania and $500,000 in California or Texas). For Amazon FBA sellers, the complexity multiplies: Amazon distributes inventory across its fulfillment network, which means a seller who sends inventory to a single Amazon warehouse may find their products stored in warehouses across 10-20 states, creating physical nexus in each one. While Amazon’s marketplace facilitator collection covers sales tax on marketplace sales in states with marketplace facilitator laws, sellers with their own websites (Shopify, WooCommerce) or who sell on platforms without facilitator collection must manage multi-state sales tax compliance themselves. For income tax purposes, the IRS treats e-commerce the same as any other retail business: IRC 471 requires businesses with inventory to account for COGS, and the gross profit (revenue minus COGS) is the starting point for taxable income.

How do e-commerce businesses minimize taxes?

How do I know if I need to collect sales tax?

Sales tax obligations depend on nexus, a connection between your business and a state that triggers a collection requirement. Physical nexus comes from having a location, employee, or inventory in a state. Economic nexus, established after the 2018 Supreme Court decision in South Dakota v. Wayfair, triggers when you exceed a state’s revenue or transaction threshold (each state sets its own figure and period; Florida and Pennsylvania use $100,000 of sales, for example, while California and Texas use $500,000). Each state sets its own rules, rates, and exemptions. If you sell online and ship to multiple states, you likely have economic nexus in several states and must register, collect, and remit sales tax in each.

What is the difference between sales tax and use tax?

Sales tax is collected by the seller at the point of sale and remitted to the state. Use tax is owed by the buyer when sales tax was not collected, typically on out-of-state purchases or items withdrawn from inventory for personal use. As a business, you owe use tax on equipment, supplies, or inventory purchased from vendors who did not charge sales tax. Many states combine sales and use tax on a single return. Failing to self-assess use tax can result in back-tax assessments for the full statute of limitations period, typically three to four years, plus interest and penalties.

Does adding a Shopify store change an FBA seller’s nexus?

Yes, in two ways. California’s rule that a seller needn’t register when all its sales go through a registered marketplace facilitator stops applying once you sell direct. And in California and New York your marketplace sales still count toward your own threshold, so the Shopify sales get tested on top of them.

Pennsylvania works differently. A marketplace seller with no physical presence there tests its $100,000 threshold on direct sales plus any marketplace sales where the facilitator doesn’t collect for it, so there it’s mainly the Shopify sales that count.

Take the example’s 15% California share: $150,000 of California sales on $1,000,000 is under California’s $500,000 line for the preceding or current calendar year, though FBA inventory stored there is its own reason to register.

Florida has its own split. Certified marketplace sales stay off your Florida return, and you register for your direct sales if you have physical presence there or your direct taxable remote sales in the previous calendar year exceed $100,000.

This guide is general information, not tax advice for your specific situation. Which points apply, and how, depends on your facts.