What is the S-corp election deadline?

The exact rule is set by IRC §1362(b)(1). The election must be made on or before the 15th day of the 3rd month of the taxable year the election is to take effect. For a calendar-year taxpayer, that's March 15. For a fiscal-year entity, it's the 15th day of the third month after the fiscal year begins.

When March 15 falls on a Saturday, Sunday, or legal holiday, the deadline shifts to the next business day under IRC §7503. In 2026, March 15 is a Sunday, so the deadline rolls to Monday, March 16, 2026. This is a year-specific quirk. The underlying rule is still March 15.

Newly formed entities have a separate window. An LLC or corporation formed during the year can file Form 2553 within 75 days of formation (technically: no more than 2 months and 15 days after the date the election is to take effect). For an entity formed mid-year, that 75-day window often extends well past March 15.

If you miss the deadline, you have options. Rev. Proc. 2013-30 provides a streamlined late-election relief procedure. If the entity intended to be an S-corp from the requested effective date, has filed all returns consistent with S-corp status (or is filing them now), and is requesting relief within 3 years and 75 days of the intended effective date, you can attach a reasonable-cause statement to a late-filed Form 2553 and get the election approved retroactively. No private letter ruling required, no fee.

Missing the deadline without late-election relief means your entity defaults to its underlying classification for the year. A single-member LLC stays a sole proprietorship, a multi-member LLC stays a partnership, and you continue paying full self-employment tax on net profit. The election then takes effect for the following tax year. At $150K or more in net profit, that's typically $8,000 to $11,000 in unnecessary SE tax for one year, which is why the deadline matters.