The most important thing to understand is that you owe the tax whether you collected it or not. Sales tax is a trust tax. You’re supposed to collect it from customers and hold it in trust for the state. If you didn’t collect it, you’re still liable for the full amount. That money comes out of your revenue, not from customers after the fact.

States can go back multiple years to assess unpaid sales tax. Most states have a 3-4 year lookback period for filed returns, but if you never filed returns at all, there’s often no statute of limitations. That means they can assess taxes from when you first established nexus, even if that was years ago.

Penalties vary by state but typically range from 10% to 25% of the tax owed. Interest accrues on top of that from the original due date. A $10,000 tax liability from three years ago could easily become $15,000 or more once penalties and interest are added. Massachusetts charges a 1% per month penalty for failure to pay, plus interest that compounds.

States are getting better at identifying businesses that should be collecting sales tax but aren’t. Economic nexus laws mean selling into a state can trigger collection requirements even without physical presence. Payment processors, marketplace facilitators, and banking data help states identify sellers who should be registered but aren’t. The days of flying under the radar are mostly over.

If you realize you should have been collecting sales tax, don’t ignore it and hope no one notices. Many states offer voluntary disclosure programs where you come forward before they find you. These programs typically reduce penalties and limit how far back the state can assess liability. Waiting until you’re audited means no negotiating leverage and full penalties apply.

Getting current requires registering with the state, calculating what you owe, and setting up systems to collect going forward. The calculation isn’t always straightforward because you need to determine nexus dates, taxable versus exempt transactions, and applicable rates for each jurisdiction.

Working with an Andover, MA bookkeeper who understands multi-state requirements can help you figure out where you have nexus and what you owe. Sales tax compliance involves registration, rate configuration, return preparation, and ongoing remittance. The cost of professional help is usually less than the penalties for continued non-compliance, and far less than the stress of facing an audit unprepared.