In most US states, marketplace facilitator laws mean Etsy, eBay and Amazon collect and remit sales tax on your behalf. Selling through your own store is different, and there the responsibility is usually yours.
The distinction that matters
If your sale happens on a marketplace, the platform generally handles the tax. If it happens on your own Shopify or WooCommerce store, you are the seller of record and you deal with registration, collection and filing yourself. Plenty of sellers run both and assume the marketplace arrangement covers everything. It does not.
Nexus in one paragraph
Nexus is the connection that obliges you to collect tax in a state. It can be physical, such as an office, staff or inventory stored in a warehouse there, or economic, triggered by passing a sales or transaction threshold. Storing stock in a fulfilment network can create nexus in states you have never visited, which surprises people every year.
Working the numbers
Use the Sales Tax Calculator to add tax to a price or to work backwards from a tax-inclusive total. Working backwards is the one people get wrong: divide the total by one plus the rate, so a $108.25 total at 8.25 percent came from a $100 pre-tax price.
Practical habits
- Keep marketplace and own-store sales separated in your records from day one. Untangling them later is miserable.
- Track where your inventory physically sits, not just where you are.
- Review thresholds annually. They change, and so does your volume.
- Do not treat collected tax as income. It is not yours.
An honest limit
This is arithmetic and orientation, not tax advice. Rates vary by state, county and product category, and nexus rules decide where you owe. Once you sell in volume across state lines, an accountant costs less than a mistake. Use the calculator for quick sums and get professional help for anything you file.