Introduction

September might not scream “tax season” the way April does, but for small business owners, it’s a critical checkpoint. Think of it like halftime in a football game. You’ve survived the first part of the year, but now you need to regroup before the high-stakes holiday sales roll in. That’s where a September Sales Tax Checklist comes in.

Many business owners push compliance tasks to the back burner, telling themselves they’ll “catch up later.” But here’s the reality: sales tax doesn’t wait. States expect accuracy, timeliness, and consistency. Miss one filing or overlook one nexus trigger, and you could face penalties, interest, or even an audit.

The good news? With the right September checklist, you can get ahead of problems before they snowball. Below, I’ll walk you through five smart steps that make up the ultimate September Sales Tax Checklist for small business compliance.

Step 1 – Review Your Nexus Obligations

First up on the September Sales Tax Checklist: nexus. Nexus is the link between your business and a state that obligates you to collect and remit sales tax there. You can have it in two ways:

• Physical Nexus: Do you have employees, offices, inventory, or warehouses in a state? If yes, you’ve likely triggered nexus.

• Economic Nexus: Even without physical presence, many states enforce nexus if your sales or transaction volume crosses their thresholds.

Here’s the kicker: thresholds change. States update their rules, sometimes subtly, and if you aren’t watching, you could already be on the hook. September is a perfect month to reassess. Look back at your year-to-date sales data and compare it against each state’s economic nexus thresholds.

👉 We’ve broken down these thresholds in detail here: Economic Nexus Thresholds for Small Business Sales Tax Compliance.

Ask yourself: Did you expand to new states through Amazon FBA, Shopify, or other platforms this year? Did your sales unexpectedly spike in certain states? If so, you might owe tax you didn’t even realize. Ignoring nexus is like ignoring a leaky faucet—it only gets worse.

Step 2 – Verify Registrations and Permits

Once you know where you have nexus, the next step in your September Sales Tax Checklist is verifying registrations. Being properly registered in each state where you owe tax is non-negotiable. Without the right permits, collecting sales tax is technically illegal.

Here’s why this matters in September:

• You’re gearing up for Q4, the busiest sales period of the year.

• If you’re missing a registration, you could collect tax unlawfully; or fail to collect it when you should. Both scenarios create headaches.

• States often cross-reference filings, so if you’re selling but not registered, it could raise a red flag.

A common mistake small businesses make is assuming marketplace facilitators like Amazon or Etsy handle everything. While those platforms may collect and remit on your behalf, you might still need to register for reporting purposes.

September is your last “calm before the storm” month. Use it to double-check your registrations, permits, and state accounts. A clean slate now prevents frantic scrambling in December.

Step 3 – Audit Your Exemption Certificates

If your business deals with wholesale customers or tax-exempt organizations, you already know the importance of exemption certificates. But are your certificates current, valid, and properly stored?

Here’s a dirty little secret: many small businesses stash certificates in random folders, let them expire, or never verify authenticity. Come audit time, missing or invalid certificates can cost you thousands.

That’s why your September Sales Tax Checklist should include an exemption certificate audit. Pull every certificate you’ve collected this year. Ask yourself:

• Is it signed and dated?

• Is it state-specific?

• Has it expired?

September is ideal because you’re far enough from year-end to fix gaps but close enough to benefit from clean records going forward.

👉 Need a deep dive? Check out our guide on Exemption Certificate Management for Small Businesses.

Think of this like cleaning out your closet. It’s not glamorous, but it keeps your compliance wardrobe in shape.

Step 4 – Reconcile Sales Data with Returns

Numbers don’t lie; but they can mislead if you’re not careful. Another must-do on your September Sales Tax Checklist is reconciling your sales data with filed returns.

Why? Because mismatched numbers raise red flags. If your sales reports say $100,000 but your filed return shows $95,000, that discrepancy could trigger questions. Even innocent mistakes can draw attention.

Here’s how to tackle it:

1. Pull year-to-date sales reports from your accounting software or e-commerce platforms.

2. Compare totals with what you’ve reported on state returns.

3. Identify gaps, mismatches, or unexplained variances.

September is perfect timing because you’ve got three quarters of data to work with. Fixing discrepancies now prevents an avalanche of corrections at year-end.

👉 Don’t forget about use tax either. Many businesses overlook it, but you’re still liable when sales tax wasn’t collected on purchases. Our article on Use Tax for Small Businesses explains why this matters.

Think of this like balancing your personal checkbook (if you still do that). If the numbers don’t line up, something’s off, and the sooner you catch it, the better.

Step 5 – Prepare for Year-End and Holiday Sales

Finally, the last piece of your September Sales Tax Checklist is forward-looking. Q4 is the busiest – and riskiest – time for sales tax compliance. High-volume sales mean more exposure, more filings, and more opportunities for errors.

Here’s how to prepare in September:

• Forecast holiday sales: Higher sales could trigger nexus in new states.

• Check filing frequencies: Some states shift businesses to monthly filing when sales increase.

• Update your systems: Make sure your POS or e-commerce platform is applying correct tax rates, including local jurisdictions.

If you’re an international seller shipping into the U.S., this is especially critical. States don’t care where you’re based; if you meet nexus rules, you’re in. 👉 Read more in our article: International Sellers Can Be Liable for Sales Tax in the U.S..

Think of it like tuning up your car before a long road trip. Skipping prep means you risk breaking down when it matters most.

Common Pitfalls Small Businesses Overlook

Even with a solid checklist, many businesses trip over the same stumbling blocks:

• Marketplace facilitator rules: Assuming Amazon handles it all when you may still need to register.

• Over-relying on software: Automation helps, but it doesn’t think critically about nexus changes.

• Forgetting local rates: State compliance is only half the story. Cities and counties may have their own rules.

Avoiding these pitfalls could save you serious money and stress.

Pro Tips to Stay Ahead Year-Round

Want to make next September easier? Try these pro tips:

• Set monthly calendar reminders to review nexus and filings.

• Keep digital folders with updated exemption certificates.

• Reconcile sales data quarterly, not just annually.

• Outsource compliance to experts when things get overwhelming.

Think of it as flossing your compliance teeth. Do a little every month, and you won’t face painful surprises later.

Why September Is the Best Time for a Sales Tax Health Check

Timing matters. Why September? Because:

• Summer sales have slowed down, giving you breathing room.

• The holiday rush hasn’t hit yet.

• You’ve got three quarters of data to review and adjust.

It’s the sweet spot for small business compliance.

How My Sales Tax Firm Can Help

Compliance doesn’t have to feel like juggling knives. At My Sales Tax Firm, we help small businesses across the U.S. stay compliant with ever-changing rules. Whether it’s nexus analysis, registrations, exemption management, or audit defense, we’ve got your back.

If your September review uncovers gaps – or if you simply don’t want the headache – we’re here to help.

Conclusion

September is your chance to get ahead of sales tax compliance. By following this September Sales Tax Checklist, you’ll:

• Reassess nexus obligations.

• Verify registrations and permits.

• Audit exemption certificates.

• Reconcile sales data with returns.

• Prepare for year-end sales.

Don’t wait until December chaos hits. Take action now and save yourself stress, penalties, and potential audits.

👉 Need help making sense of your obligations? Talk to the experts at My Sales Tax Firm today.