Can I efile an S corp 2024 1120S after the 9/15/25 due date
Yup
I'll second that and add that 3 years are open at a time for e-filing - star date 9.23.2025.
yes, but not for the month or two the IRS shuts down the efile system to update for the new year. usually end of November to mid January (although I think it will be longer this year) But in general you can e-file anytime for the 3 open years.
