C-Corp Return Deadline — April 15

Who must file or pay

All C-Corporations with a December 31 fiscal year-end must file Form 1120 by April 15.

What you need to know

Calendar-year C-Corporations file Form 1120 by April 15. This is the same date as individual returns, meaning founder-shareholders face multiple simultaneous deadlines: the corporate return, their personal K-1-driven return, and Q1 estimated taxes.

Note: Delaware C-Corps (the most common startup structure for QSBS-eligible companies) have no state income tax on out-of-state revenue, but must still file a Delaware franchise tax report by March 1 (a separate obligation from the federal return). The Delaware franchise tax due date is earlier than the federal deadline.

QSBS eligibility (up to $10M in capital gains exclusion under IRC §1202) depends on meeting specific requirements at the time of stock issuance. TaxosAgent verifies QSBS eligibility as part of C-Corp tax strategy reviews.

Failure-to-file: 5% of unpaid tax per month, up to 25%. If a C-Corp owes $50,000 and misses the deadline by 5 months, the late-filing penalty alone is $12,500.

Required forms

• →Form 1120
• →Form 7004 (extension)

Go deeper

A licensed TaxosAgent professional reviews your situation before this deadline — so you maximize savings, not just compliance.