US sales tax. Nexus and registration

US sales tax is per-state, per-city, sometimes per-district. Here's the map.

Where you owe

You owe sales tax in any state where you have nexus. Two kinds:

• Physical nexus. Office, warehouse, employee, or inventory in the state. Permanent
• Economic nexus. Over a threshold of revenue or transactions in the state per year. Most states: $100k revenue OR 200 transactions. Some are higher (TX: $500k), some lower (KS: any sale)

Crossing economic nexus typically gives you 30-90 days to register before back-tax penalties start.

SellStein automatic tax

Settings → Tax → US → Automatic. We pull rates per state, per city, per ZIP, per shipping address. Calculates at checkout in real time. Updates nightly.

We don't register or file for you. That's still your responsibility (or a tax service like Avalara, TaxJar, Anrok).

Marketplace facilitator law

If you sell on Amazon, Etsy, or eBay (not your own SellStein store), those marketplaces collect and remit sales tax for you in most states under MPF laws. Your SellStein store is YOUR storefront. MPF doesn't apply. You're the merchant.

Registration

Per state. Most states have an online registration through the Department of Revenue website. You'll need:

• EIN
• Business address
• Estimated annual revenue in the state
• NAICS code

Takes 1-3 weeks to get a sales tax permit. Some states (Florida, California, Texas) issue immediately.

Filing

Frequency depends on volume:

• Annual. Under $1k tax/year
• Quarterly: $1k–10k tax/year
• Monthly. Over $10k tax/year

States set this when they issue your permit. SellStein's Tax Reports (Reports → Tax → State summary) gives you the exact filing-ready totals per state per period. Copy-paste into the state's online filing form.

Common mistakes

• Forgetting Wayfair states. Economic nexus came from the 2018 Wayfair v. South Dakota ruling. Many sellers haven't updated their state list since then. Re-audit yearly
• Mixing exempt and taxable products. Clothing is exempt in PA, taxable in CA. Per-product tax codes (Settings → Tax → Tax codes) handle this; the default rate doesn't
• Free shipping is sometimes taxable. In some states, the cost of shipping is taxable as part of the sale. Automatic tax handles this if you label shipping correctly

When to call a CPA

When you cross nexus in 5+ states, the filing burden becomes a job. Outsource it. Anrok, TaxJar, and Avalara specialize in multi-state SaaS-style filing for small merchants. Cost: $1-3k/year, saves you 40+ hours.