When Is Sales Tax Due in September 2026? Every State's Filing Deadline

Texas: September 21 — Not September 22

Texas is the most commonly missed deadline this month — and the reason catches businesses off guard every time.

Texas shifts to the next business day after a weekend — which in September 2026 is Monday, September 21, not Tuesday September 22 like most other states.

According to the Texas Comptroller, a $50 penalty applies per late return immediately, plus 5% of any tax due if filed within 30 days of the deadline, or 10% if more than 30 days late. Put September 21 on your calendar specifically for Texas — not September 22.

Florida: Electronic Payment Must Be Initiated September 19

Florida is the state that generates the most avoidable late penalties — because of a rule most businesses don't know exists.

The Florida Department of Revenue requires that electronic payments be initiated the business day before the due date. The standard Florida monthly deadline is September 22 — but electronic filers must initiate their payment by Friday, September 19.

If you initiate your Florida electronic payment on September 22, it will be processed late. The penalty clock starts immediately — 10% of tax due for the first 30 days, increasing after that.

Put September 19 on your calendar as your Florida action date. File and initiate payment by end of business Friday, September 19.

The Non-Standard State Deadlines

Not every state uses September 22. Here are the states with different September deadlines.

Maine — September 15 — already passed. Maine is the only state with deadlines on the 15th of the month. If you file in Maine and haven't filed yet, penalties are already accruing at 1% per month up to 25% of tax due. File immediately.

Ohio — September 23. Ohio is the only state with deadlines on the 23rd of the month. Ohio monthly filers have until September 23 — one day after the standard deadline.

Washington — September 25. Washington has deadlines on or before the 25th of the month. Washington monthly filers have until September 25. Given that Washington processed 864 local rate changes on July 1, verify your August returns reflect the updated rates for every affected delivery address before filing.

Kansas, New Mexico, and Vermont — September 25. All three states have deadlines on the 25th or next business day. Monthly filers in these states have until September 25.

Massachusetts — September 30. Massachusetts has deadlines on or before the 30th of the month — the latest standard deadline of any state. Monthly filers in Massachusetts have until September 30. Note: if you had Massachusetts sales during the August 8-9 tax-free weekend, verify your system correctly exempted qualifying items under the $2,500 threshold before filing your August return.

California — September 30. California monthly filers have until September 30. Verify your August filings reflect any local rate changes that took effect in your delivery ZIP codes before submitting.

Alaska — September 30. Alaska has no statewide sales tax, but local jurisdictions collect their own. If you're registered in Alaskan localities, verify your specific due dates with each jurisdiction.

August's Back-to-School Holiday Transactions Hit September Returns

This month's filing period includes one of the most compliance-intensive weekends of the year — the August 7-9 multi-state holiday cluster. As Avalara's 2026 sales tax holidays guide details, the August 7-9 weekend involved simultaneous holidays across Iowa, Texas, Ohio, Missouri, Oklahoma, South Carolina, Virginia, and Illinois — plus Massachusetts starting August 8. Before you file your September returns, audit those transactions carefully.

Iowa: Two-day holiday only — Friday and Saturday. Verify Sunday August 9 transactions were taxed normally. Iowa's holiday closed at midnight Saturday.

Texas: Clothing, footwear, school supplies, and backpacks under $100 exempt August 7-9. Verify no tax was collected on qualifying items and that non-qualifying items were taxed normally.

Ohio: Traditional format only — clothing under $75, school supplies under $20. Verify your system didn't apply the expanded 2025 format. Ohio's expanded holiday was canceled for 2026.

Illinois: Reduced rate holiday — 1.25% state rate on qualifying clothing and footwear under $125 through August 16. Verify your August return shows the reduced state rate — not zero — on qualifying Illinois transactions. Local taxes continued at normal rates throughout.

Massachusetts: Full exemption on most items under $2,500 for personal use, August 8-9. Mandatory participation means any August Massachusetts return showing tax collected on qualifying items during those two days creates an over-collection liability.

South Carolina: No price caps on qualifying clothing, computers, and supplies. Verify your system didn't apply a $100 clothing cap to South Carolina transactions.

Getting these configurations wrong in your August transactions creates errors in your September returns that may trigger review. For a full breakdown of every state's holiday rules, visit our complete August 7-9 holiday compliance guide.

Indiana Tax Amnesty Closes September 9 — 8 Days Away

This is the most urgent compliance deadline happening this month — separate from regular filing obligations.

Indiana's Tax Amnesty 2026 closes September 9 — 8 days from today. The program waives all penalties, interest, and collection fees on pre-2024 Indiana liabilities for businesses that enroll and pay or establish a payment plan before that date. We covered every detail of the program — including the double penalty warning and the audited businesses exception — in our Indiana amnesty final warning article

If you have any pre-2024 Indiana sales tax liability — filed or unfiled — the September 9 deadline is more urgent than any filing deadline this month. After September 9, the amnesty closes permanently. The next Indiana amnesty, if historical patterns hold, won't come until 2036.

What Q3 Quarterly Filers Should Be Doing Right Now

If you file quarterly, your Q3 return isn't due until October 20. But September is the month to prepare — not October.

Your Q3 covers July 1 through September 30. Here's what to focus on in the next three weeks.

Review your July 1 rate change compliance. July 1 brought 1,340 sales tax changes across 20-plus states — including Illinois processing 202 local changes, Washington processing 864, Mecklenburg County jumping from 7.25% to 8.25%, Alabama's grocery tax returning, Colorado's retail delivery fee increasing to $0.31, and Nebraska repealing multiple exemptions. Avalara's July 2026 rate changes summary has the full breakdown. Verify your Q3 collections reflect the updated rates from July 1 onward — not the prior rates.

Check for new nexus states. If your sales crossed an economic nexus threshold in a new state during Q2, you may have had an unfiled Q2 obligation. Assess your Q2 filing accuracy before Q3 adds another period on top of any existing gap.

Renew expired exemption certificates. Any resale or exemption certificate that expired during Q2 or early Q3 needs to be renewed before you file your October return. Missing certificates are a primary audit trigger — particularly as states deploy AI-powered audit selection tools that specifically flag exemption certificate gaps.

Audit your back-to-school holiday configurations. Verify your August 7-9 holiday transactions are correctly categorized before those transactions roll into your Q3 return due October 20.

Monitor Washington D.C.'s October 1 rate change. Washington D.C.'s general sales tax rate increases from 6.5% to 7.0% on October 1, 2026 — the first day of Q4. If you sell taxable goods, digital products, or SaaS to D.C. customers, your Q4 rate needs to be updated before October 1. We covered every detail in our Washington D.C. rate change article.

The Zero Return Requirement

One of the most common compliance mistakes for businesses that expanded into new states: skipping returns in months with no taxable sales.

Registering in a state creates a filing obligation — permanently, until you formally close your account. A month with no taxable sales doesn't mean no filing requirement. It means a zero return is due on the same schedule as every other month.

If you registered in any new states in 2026 and had months with no taxable sales into those states, verify zero returns were filed on time. States with automated matching systems are increasingly flagging registered businesses that have gaps in their filing history — even zero-liability gaps.

The Penalty Stakes — September's Worst-Case Scenarios

Missing a September sales tax deadline costs more than the tax owed. Here's what's at stake in the states where penalties hit hardest.

Washington — 9% after the due date, 19% after the last day of the following month, up to 29% after the second month. The steepest penalty structure in the country.

California — 10% of tax due for late filing, with daily interest accruing. For high-volume California sellers, a missed September 30 deadline compounds quickly.

Texas — $50 per late return immediately, plus 5% of tax due within 30 days, 10% beyond 30 days. Missing the September 21 Texas deadline by even one day triggers the immediate $50 per-return penalty.

Illinois — 2% penalty on unpaid tax, plus 20% if the return isn't filed within 30 days of the due date.

New York — 10% for late filing, with additional penalties for businesses with a pattern of late filings.

Your September Compliance Checklist

Three weeks is enough time to handle everything — if you start today.

For monthly filers: Reconcile your August transaction data by jurisdiction. Audit your August 7-9 holiday transactions for correct exemption application. Initiate Florida's electronic payment by September 19. File Maine immediately if you missed September 15. Put Texas on September 21 — not September 22. Verify Washington, Kansas, New Mexico, and Vermont are calendared for September 25. Schedule Massachusetts and California for September 30.

For quarterly filers: Review Q3 July and August collections for rate accuracy against July 1 rate changes. Assess Indiana amnesty eligibility before September 9. Renew expired exemption certificates. Update your D.C. rate to 7% before October 1. Start preparing your Q3 return data now so October 20 isn't a scramble.

For all businesses: File zero returns on time for every registered state with no taxable sales. Verify your filing frequency hasn't been adjusted by a state without your noticing — states can change filing frequency as your revenue grows, sometimes without prominent notification.

Not sure whether your September filings are on track across all your registered states — or concerned that the July 1 rate changes or August holiday transactions created compliance gaps in your Q3 records? Book a free consultation with our team at sales.tax. We'll audit your filing calendar, verify your rate accuracy, and make sure nothing falls through the cracks before September 22.