The tax deadline for S Corporation filing of a tax return is always by the 15th day of the third month that follows the end of the tax year. This is generally March 15. 

Information About Filing an S Corporation Tax Return

An S corporation is considered a "pass-through" entity. This means the responsibility of filing a tax return is the responsibility of the individual shareholder. The profits and losses from the corporation are reported on each shareholder's personal income tax return. 

The S corporation is not form-free. It must still file an informational tax return annually in addition to other Internal Revenue Service (IRS) forms such as withholding taxes from employee compensation.

An S corporation files all its financial activity of IRS Form 1120S along with a Schedule K-1 for each of the corporation's shareholders. The Schedule K-1 reports the taxable income of a shareholder's share of the business on their individual tax return.

Shareholders paying tax on corporate income must follow the same filing deadlines imposed by the IRS on individual taxpayers, which is usually April 15.

S corporations unable to file by the March 15 deadline can obtain a six-month extension, automatically, by filing Form 7004 from the IRS. Generally, to obtain an automatic extension, Form 7004 is filed by the regular due date of the tax return.

Form 1120S Filing Deadline

Step 1. File Form 1120S and pay taxes due to the IRS by March 15; September 15 if an automatic six-month extension was obtained. 

Step 2. Provide each shareholder with a copy of Schedule K-1 or a Schedule K-1 substitute.

Step 3. A corporation that has been dissolved must file by the 15th day of the third month after the date of dissolution.

Step 4. Due dates that fall on the weekend or a legal holiday, can't be filed until the following day that is not either a holiday or a weekend day.

Step 5. For S corporations that terminate its election as an S corporation during the tax year and revert to a C corporation, Form 1120S is filled for the S corporation's short portion of the year by the date due, including extensions, of the short portion of the year of the C corporation.

Quarterly Tax Return Deadlines

S corporations paying wages to employees are responsible for withholding Social Security, Medicare, and federal withholding taxes from their paychecks.

IRS Form 941 is filed by the S corporation each quarter to report and remit the aggregate amount that was withheld. 

The due dates for Form 941 fall quarterly (four times a year) with the due dates being January 31, April 30, July 31, and October 31.

Unemployment Tax Filing Date

An annual Federal Unemployment Tax Return is also required each year using Form 940 for S corporations with employees.

There are two instances when an S corporation must file Form 940 — when wages of $1,500 or more are paid in any calendar quarter, or if the corporation has at least one employee who is working a portion of a day in 20 separate weeks or more. 

The purpose of Form 940 is the reporting the amount of the wages owed by the S corporation for unemployment taxes, which the corporation must remit to the IRS.

The standard due date for filing Form 940 is January 31. This date may be extended to February 10 if the corporation is paying the entire tax on time.

Late Filing Penalties

  • If Form 1120S is not filed by the standard due date or the extended due date, the minimum penalty imposed by the IRS is $195 for each month or part of the month the return is late. The $195 is multiplied by the number of shareholders in the corporation. 
  • If Form 941 is filed after the deadline by the corporation and there is an unpaid balance remaining, the penalty is 5 percent assessed on the balance for each month or partial month the tax remains late. The percentage can go up to a maximum of 25 percent. 
  • Form 940 has similar penalties for filing after the due date.

Income Tax Deadlines

  • Partnership returns (Form 1065) — March 15, 2018
  • C corporation returns (Form 1120) — April 17, 2018
  • S corporation returns (Form 1120S) — March 15, 2018

If you need help with the tax deadline for an S Corporation, you can post your legal need on UpCounsel's marketplace. UpCounsel accepts only the top 5 percent of lawyers to its site. Lawyers on UpCounsel come from law schools such as Harvard Law and Yale Law and average 14 years of legal experience, including work with or on behalf of companies like Google, Stripe, and Twilio.