File form 2553. The IRS requires that the form is filed within 2 months and 15 days after the beginning of the tax year that the election is to take effect. For example, a business with a 12/31 year end has to file form 2553 by March 15th. Don’t worry, you can request an exception if you realize after March 15th that you will want to make the S-corp election for that year.