September 15: A Triple Deadline for Contractors Who Made the S-Corp Election
September 15 is one date with three deadlines stacked on it. If you run your construction business as an S-corp, all three can land on you in the same week, and most contractors only have one of them on the calendar.
Here is the situation for a lot of trade business owners right now. You had a strong summer. Cash came in on big jobs, you paid the crew, you bought a piece of equipment, and you have not looked hard at the tax side since spring. Then September shows up. The S-corp election for contractors is one of the most common strategy moves we put in place, and this is the week it quietly tests whether yours was set up right or just filed and forgotten.
Here is what actually falls on September 15, and what each piece means for a contractor.
Deadline one: your Q3 estimated tax payment
The IRS wants tax paid as you earn it, not in one lump next April. For income earned June through August, the third-quarter estimated payment is due September 15. Miss it or lowball it and you can owe an underpayment penalty, which is effectively interest on the tax you should have already sent in.
Contractors get tripped up here more than most business owners, and it is not carelessness. Your income is lumpy. A framer or remodeler might run three slow months and then bill $180,000 across one busy stretch. A generic "pay a quarter of last year's tax each quarter" rule does not fit income that arrives in waves tied to your project schedule and the weather.
If your S-corp is running payroll correctly, some of your tax is already being withheld through your own paycheck, which changes the estimate math. That is the point most owners miss when they DIY the number.
Deadline two: the extended S-corp return
If your S-corp filed for an extension back in March, the extended return is due September 15, not October 15. October is the individual deadline. The business return comes a month earlier, and the two get mixed up constantly.
This matters because your S-corp return produces the K-1 that flows to your personal return. If the business filing is late, the penalty is not based on tax owed. It is a flat charge per shareholder per month. For a single-owner construction S-corp that penalty starts around $245 for each month it is late. It climbs fast and it is fully avoidable.
Deadline three: the checkpoint most contractors skip
The third deadline is not on any IRS notice. September 15 is the natural point to check whether the S-corp election is doing its job with three and a half months still left to fix it.
Two numbers decide whether an S-corp saves a contractor money: the salary you pay yourself and whether payroll is actually being run. A reasonable salary is the wage the work would cost you to hire out. Set it too high and nearly all your income runs through payroll taxes, which erases the savings the election is supposed to create. Set it too low with no payroll at all and you are carrying real risk if the IRS ever looks. We have picked up new clients who elected S-corp status on their own, never ran a paycheck, and were sitting on a problem they did not know they had.
By mid-September you know roughly what the year looks like. There is still time to true up your salary, catch up payroll if it slipped, and size the Q3 payment to reality instead of a guess.
What to do this week
Pull three numbers before September 15: your net income so far this year, the salary you have actually paid yourself through payroll, and what you sent the IRS for Q1 and Q2. Those three tell you whether your estimated payment is close and whether your election is still set correctly for the income you are on track to earn. If you filed a business extension, confirm the return date with whoever prepares it, and confirm it is September 15, not October.
If you made the S-corp election on your own and have never had someone pressure-test the salary and the payroll, this is the week it is worth an hour.
Schedule a call here. We will look at your numbers, tell you whether the election is set up right for what you are actually earning, and size the payment so September 15 is not a surprise.