Whether you use FBA or a US warehouse, whether you sell mainly through marketplaces or your own store, and whether any single state has passed roughly $100,000 or 200 transactions: these three things decide whether you need to register for sales tax and whether marketplace collection covers you fully. Answer 3 questions and see your gaps right away.
US sales tax is a state (and local) tax, separate from federal corporate income tax. Whether a seller must register, collect and file depends on whether it has nexus with the state. There are two common triggers. Physical nexus comes from people, offices, your own warehouse, or inventory held in FBA or third-party warehouses in the state. Economic nexus can arise with no physical presence at all, once sales or order counts pass a threshold. This self-check uses the common economic threshold of about $100,000 in annual sales or 200 transactions per state, and flags that some states, such as California, Texas and New York, commonly use different figures like about $500,000. There is no single national rule.
Your sales channels change what you actually carry. On Amazon and other marketplaces, many states have the marketplace facilitator collect and remit sales tax on marketplace orders. Orders from your own store, your brand site or channels that don't collect for you are still yours to assess for nexus, register and collect on. Plenty of sellers assume "the marketplace collects, so I'm covered nationwide", and the gap shows up the moment they open a Shopify store or a state falls outside marketplace collection.
FBA or US warehouse inventory usually creates physical nexus in the state where it sits, so you need to assess registration there even if your sales are below the economic threshold. If inventory is spread across several states, build a state-by-state priority list: which states you register in because of inventory, which because of $100,000/200 transactions (or the state's own $500k-type threshold), which orders the marketplace already collects on, and which you must collect on yourself.
No. It is the common economic nexus threshold this tool uses so you can get a first-pass read. State laws are not uniform: some states (the tool gives CA, TX and NY as examples) may use other figures such as about $500,000. Always go by the state's current rules, including whether marketplace sales count toward the threshold.
Marketplace collection mainly covers orders the marketplace facilitates. If you also sell through your own store, wholesale or other channels that don't collect for you, or a state still requires sellers to register, you can't assume "marketplace means no obligations". Look at each channel separately.
Many states treat inventory in the state as a key factor for physical presence. States where your FBA inventory sits should usually be first in line for a registration review, whatever your economic threshold numbers say.
Even below the economic threshold, inventory or staff can still create physical nexus, and some transaction types, local taxes or voluntary registration choices need case-by-case review. A "lower pressure" result does not mean you will never have a filing obligation.
No. The result is a risk tier and action checklist based on the channel, FBA inventory and threshold options you chose. It is not a tax authority assessment. Next, export sales and order counts by state, compare them with current thresholds and marketplace coverage, then register and catch up where needed.