The normal timing rule
To make an S corporation election, an eligible corporation or entity generally files Form 2553 no more than 2 months and 15 days after the beginning of the tax year the election is to take effect, or at any time during the preceding tax year.
For an existing calendar-year business seeking S status effective January 1, the familiar target is March 15, adjusted to the next business day when necessary. For 2026, March 15 is a Sunday, so the IRS calendar places the deadline on March 16, 2026.
New entities can have a different date
A newly formed entity whose first tax year starts after January 1 does not simply use March 15. The Form 2553 instructions calculate the window from the actual beginning of the first tax year. This is one reason formation date, first ownership, first assets, and start of business should be documented accurately.
Eligibility matters before timing
A timely filing does not fix an ineligible ownership structure. S corporations have statutory eligibility requirements, including restrictions on the type and number of shareholders and on classes of stock. Review eligibility before asking payroll or bookkeeping to operate as though the election were already effective.
Late-election relief exists, but do not plan around it
The IRS provides procedures that can grant relief for some late S elections when the requirements are met, including reasonable-cause and consistency requirements. Relief is valuable when a legitimate mistake occurred; it should not replace a reliable formation-and-tax calendar.
Operational follow-through
Once an S election is effective, the company still needs payroll, bookkeeping, shareholder-basis support, state treatment review, and an annual Form 1120-S. The election is one form; operating correctly under the election is the recurring work.