S Corporate Tax Extension Deadline 2025. If you’re a calendar year filer, april 15, 2025, is also the deadline to file your c corporation’s federal tax return for 2023 or to file for an extension. Key tax deadlines are coming up in 2025 for llc and corporation businesses.

For businesses already operating as s corps, march 15th holds significance as the deadline for filing the s corp tax return, form 1120s. The s corp tax due date may be different for small.