For a corporation to be an S Corporation, the paperwork to make that effective is due no more than two months and 15 days after the beginning of the tax year the election is to take effect (yes, I copied that from the IRS instructions). If you’re really ahead of the game, then anytime during a tax year preceding the year you want it to be in effect. For new corporations, the tax year typically begins on a day other than January 1, unless you formed on that date. So, for example, if your corporation was formed on July 8, then the S Corp election would be due 15 days after September 7, or September 22.