Before you can file sales tax anywhere, you need to know where you actually have obligations. Since the 2018 Wayfair Supreme Court decision, states can require you to collect and remit sales tax even without a physical presence there. Most states now have economic nexus thresholds, typically $100,000 in sales or 200 transactions per year in that state. Cross either threshold and you owe that state sales tax on future sales.

Register for a sales tax permit in each state where you have nexus. Every state has its own registration portal and process. Some states participate in the Streamlined Sales Tax program, which lets you register in multiple participating states with one application. Others require separate registrations. Keep your permit numbers organized because you’ll need them for every filing.

Each state assigns a filing frequency based on your sales volume there. High-volume sellers file monthly. Lower-volume sellers might file quarterly or annually. The due dates aren’t uniform either. Some states want returns by the 20th of the month, others by the last day. Miss a deadline and you’re facing late fees and penalties even if you don’t owe any tax that period.

Rates differ not just by state but by city and county within states. California alone has over 400 different tax rate jurisdictions. Beyond rates, the rules for what’s taxable vary too. Some states tax SaaS subscriptions, others don’t. Some tax clothing, others exempt it. Getting this wrong means you either overcharge customers or underpay the state and face an assessment later.

Manual multi-state sales tax compliance becomes unworkable past two or three states. Software like Avalara, TaxJar, or built-in tools in Shopify and Amazon can calculate rates automatically at checkout, track where you have nexus, and generate returns for each state. Integration with your sales platforms means you’re not manually entering transactions.

Even with software, someone needs to set it up correctly, monitor nexus thresholds, file the returns, and make the payments on time. Many businesses hand this off to a San Diego bookkeeper or accountant who specializes in it. That way returns get filed correctly, exemption certificates get tracked, and you’re not spending hours every month navigating multiple state portals.

If you’re behind on registrations, start by figuring out where you currently have nexus. Look at last year’s sales by state and compare them to each state’s threshold. Register where you’ve exceeded the limit and begin collecting tax going forward. For past periods where you should have been collecting but weren’t, talk to a tax professional about voluntary disclosure programs that can reduce penalties.