S-Corp Election Deadline
The deadline to elect S-Corporation tax treatment depends on whether your business is newly incorporated or is in its second (or later) tax year.
For a New Business
A corporation or LLC must file an S-Corp election within two months and 15 days (~75 days total) of the date of formation for the election to take effect in the first tax year.
For an Existing Business
To make an election in subsequent years, you may file the election at any point from the first day of your preceding tax year up to two months and 15 days after the start of the applicable tax year. Note that conversion of your tax structure can have complex tax implications; consult your tax professional for personalized advice.
For more detailed information on these rules and relief for late election, please see Instructions for Form 2553