When are S corporation tax returns due? Although S corporations do not pay federal income tax at the corporate level, they must file an annual informational return. For S corps that follow the calendar year, this return (Form 1120S) is due by March 15. For those that observe a different fiscal year for taxation, the form is due by the 15th day of the third month after the fiscal year closes.

Filing S Corporation Taxes

Form 1120S must include a Schedule K-1 for each shareholder detailing his or her portion of the company's profits and losses. These are reported on the shareholder's individual tax return, a structure known as pass-through taxation. The due date for the Schedule K-1 is the same as for the informational return.

If your S corp is unable to submit these forms to the IRS by March 15 or the fiscal year deadline, you can receive an automatic six-month extension if you file Form 7004. Shareholders must submit their Schedule K-1 forms with their individual tax returns, which are typically due by April 15. When this date falls on a weekend, the deadline is the next business day (April 17, 2018, for example).

S corporations that pay employee wages must withhold federal income tax and FICA (Social Security and Medicare) tax from their paychecks. These withholdings must be filed each quarter by submitting Form 941 every quarter and remitting the withholdings to the IRS. The due dates are January 31, April 30, July 31, and October 31.

S corporations that pay employee wages of at least $1,500 in a given calendar quarter or employ at least one person for at least part of a day in at least 20 weeks must file Form 940 to report annual federal unemployment taxes (FUTA). This form must be filed by January 31 each year. If you are paying all outstanding unemployment taxes with your filing, the deadline is extended to February 10.

S corporations that sell certain products and services, such as gasoline, betting, and indoor tanning, must also file monthly excise taxes using Form 730.

Important 2018 Tax Deadlines

S corporation owners should note the following important tax deadlines for 2018.

  • January 16: Fourth quarter 2017 estimated tax payment is due.
  • January 31: Employers must mail their employees W-2 forms and provide 1099s for nonemployee compensation and payment of dividends, interest, and retirement plan distributions.
  • February 15: Financial institutions must mail Form 1099-B to record sales of bonds, stock, or mutual funds; Form 1099-S for real estate transactions; and Form 1099-MISC for payments reported in boxes 8 or 14.
  • February 28: Businesses that are filing on paper must submit Forms 1096 and 1099 to the IRS.
  • March 1: Farmers and fisherman must file their 2017 tax returns.
  • March 15: Partnerships must file their 2017 tax returns and provide partners with their Schedule K-1 forms if applicable.
  • March 31: Deadline for filing Forms 1096 and 1099 electronically.
  • April 17: Deadline to file individual 2017 tax returns or request an extension with Form 4868.
  • April 17: First estimated 2018 tax payment due.
  • June 15: Second estimated tax payment due.
  • September 17: Third estimated tax payment due
  • October 1: Deadline for small employers to set up an IRA.
  • October 15: Final deadline to file 2017 individual tax returns.
  • January 15, 2019: Fourth estimated 2018 tax payment due.

Late Filing Penalties

S corporations are subject to a $195 minimum penalty for each month or portion of a month the return is late, multiplied by the number of shareholders. For example, an S corp with two shareholders that files late will owe $290 a month until the taxes are filed.

Companies that file Form 941 late and have unpaid taxes are subject to a 5 percent penalty of the unpaid amount each month, capped at a maximum of 25 percent.

If you've mixed a tax deadline, file your forms with the IRS and pay your unpaid taxes as soon as possible. Your payment and forms will be processed faster if you go online and use IRS Direct Pay. S corporations should establish a reliable year-round accounting system to avoid late tax filings.

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