Business Tax Deadlines are a critical part of running a trade business—whether you’re a contractor, electrician, plumber, or builder. Beyond the jobsite challenges, one of the biggest administrative hurdles is staying compliant with IRS due dates, and September 15 is one of the most important dates to know.
Missing this deadline could result in penalties, interest charges, and unwanted IRS scrutiny. Whether you operate as an LLC, S Corporation, or partnership, this guide from James D. Miller CPA will break down the essential business tax deadlines you need to know—especially the September 15 deadline—and how tax extensions can help you stay in control.
Why September 15 is a Big Deal for Trade Businesses
If your business is structured as an S Corporation, partnership, or multi-member LLC, your federal tax return is typically due by March 15 each year. However, if you filed for an extension, you’re granted six more months—making September 15 your final deadline.
That makes September 15 the true last chance to file:
- Form 1120-S for S Corporations
- Form 1065 for Partnerships
- All related Schedule K-1s to shareholders or partners
This deadline is non-negotiable—missing it could mean late filing penalties, delayed tax credits for your partners, or IRS notices you don’t want in your mailbox.
What You Should Have Ready by September 15
To meet the September 15 deadline, make sure these items are prepared and reviewed:
- Accurate year-end financials (profit and loss statement, balance sheet)
- Reconciled bank and credit card accounts
- Final payroll records and contractor payments
- Owner distributions and capital contributions
- Loan documents or depreciation schedules
- 1099s and W-2s issued during the year
- Schedule K-1s—reports each partner’s or shareholder’s share of income, deductions, and credits
James D. Miller CPA helps tradesmen organize these records and prepare filings efficiently so you meet IRS standards without scrambling at the last minute.
What Happens If You Miss the Deadline?
Missing the September 15 deadline can trigger:
- Late filing penalties – $245 or more per shareholder/partner, per month (up to 12 months)
- Delayed refunds or loss of deductions
- IRS notices or audits due to missing documentation
- Disruption for your partners or investors waiting on K-1s for their personal taxes
A late tax return could also impact your eligibility for certain loans or bonding required in trade and construction projects.
What About C Corporations?
If you operate as a C Corporation, your tax return (Form 1120) is due on:
- April 15 for calendar-year businesses
- Or the 15th day of the fourth month after your fiscal year-end
If you filed Form 7004 for an extension, your new deadline is October 15. That gives you extra time, but not extra leniency—you still must pay any taxes due by the original due date to avoid penalties.
How to Use Tax Extensions Wisely
Extensions are a useful tool—not a red flag.
By filing Form 7004 before your original deadline (March 15 for S Corps/Partnerships, April 15 for C Corps), you buy yourself time to:
- Finalize financials
- Correct reporting errors
- Consult with your CPA
- Avoid hasty or inaccurate filings
However, extensions don’t extend your payment due date. If you expect to owe taxes, you should estimate and pay by the original deadline to avoid interest or penalties.
Pro Tip: Plan Year-Round, Not Just Before Deadlines
One of the best ways tradesmen and contractors can stay ahead of tax deadlines is with year-round planning.
At James D. Miller CPA, we work with trades-based businesses to:
- Track expenses and deductions throughout the year
- Forecast quarterly payments and year-end liabilities
- Organize financial records for faster filing
- Offer proactive reminders before critical deadlines
This keeps you ready—not reactive—and protects your bottom line.
Summary of Key Business Deadlines
| Deadline | Applies To | Forms |
|---|---|---|
| March 15 | Partnerships, S Corps (original) | 1065, 1120-S, K-1s |
| April 15 | C Corporations (original) | 1120 |
| September 15 | Partnerships, S Corps (extended) | 1065, 1120-S, K-1s |
| October 15 | C Corporations (extended) | 1120 |
Final Thoughts
Contractors and tradesmen already juggle a lot—don’t let missed tax deadlines cost you more time, stress, or money. With expert planning and timely filing, you can focus on growing your business while staying in the IRS’s good graces.
James D. Miller CPA is here to help you navigate every deadline, extension, and return with accuracy and confidence.
Don’t let September 15 sneak up on you.
Schedule a tax review or filing consultation with James D. Miller CPA today—and make your business tax-smart all year long.