C Corp Compliance 2025
A definitive guide to IRS reporting requirements, filing deadlines, and audit defense strategies for the modern C Corporation.
Executive Summary
Compliance for C Corporations is a high-stakes ecosystem. Beyond the annual Form 1120, corporations must navigate quarterly Estimated Tax Payments, strict Information Reporting (1099s), and complex international disclosures.
In 2025, the IRS is ramping up enforcement on High-Income/High-Wealth entities and using AI to target Transfer Pricing anomalies. "Set it and forget it" is no longer an option; proactive risk management is essential.
The Deadline
The Trigger
The Mandate
2025 Compliance Calendar
| Date | Filing / Payment | Details |
|---|---|---|
| Jan 31 | W-2s & 1099-NEC | Strict deadline. Penalties apply per form for late filing. |
| Mar 15 | S Corp Deadline | Deadline for 1120-S (if not C Corp). |
| April 15 | Form 1120 Due | Primary C Corp Return. Payment of tax due. |
| April 15 | Q1 Estimated Tax | 25% of annual estimated liability. |
| Oct 15 | Extended Return | Final deadline if Form 7004 was filed. |
IRS Audit Triggers (2024-2025 Trends)
Consecutive Losses
Reporting losses for multiple years while operations continue can trigger a "Hobby Loss" or "Economic Substance" audit.
Transfer Pricing
Large payments to foreign affiliates (royalties, management fees) are scrutinized for profit shifting. Documentation is key.
Officer Compensation
Paying officers excessive salaries (to dump profits) or too little (to avoid payroll tax, though less common in C Corps) attracts attention.
Information Mismatch
If your 1120 revenue doesn't match the 1099-K / 1099-NEC forms filed by your clients, automated underreporter notices (CP2000) are sent.