The Wayfair world

Since South Dakota v. Wayfair (2018), you no longer need a physical presence in a state to owe sales tax there. Economic nexus — typically $100,000 in sales or 200 transactions in a state per year — is enough to create a filing obligation. For a growing SMB selling across state lines, this is the single biggest compliance trap.

Know where you have nexus

You may have nexus from:

Physical presence — an office, employee, inventory, or even a remote worker in the state.
Economic activity — crossing the state's sales or transaction threshold.
Marketplace activity — though marketplaces often collect on your behalf, you may still need to register.

Track sales by ship-to state monthly so you see a threshold approaching before you cross it.

Register before you collect

You must register for a sales-tax permit before collecting tax in a state — collecting without a permit is itself a violation. Once registered, you're on the hook to file even in periods with zero tax due ("zero returns").

Handle exemptions correctly

Sales to resellers and certain nonprofits are exempt, but only if you collect and retain a valid exemption certificate on file. An uncollected certificate means you owe the tax in an audit, even if the sale was genuinely exempt. Re-validate certificates annually.

File on time, every time

Calendar every filing frequency — states assign monthly, quarterly, or annual based on volume.
Reconcile collected tax to remitted tax each period; the difference is a liability on your balance sheet, not revenue.
Don't spend the tax you collect. Sales tax is money you hold in trust for the state. Treat it as untouchable.

When in doubt, get help

Multistate sales tax is genuinely complex. If you're approaching nexus in five or more states, the cost of automation or a specialist is far less than the penalties and back-taxes from getting it wrong.

Sales-Tax Compliance for Growing SMBs

The Wayfair world

Know where you have nexus

Register before you collect

Handle exemptions correctly

File on time, every time

When in doubt, get help

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