A domestic corporation must file an income tax return for every year it exists, even if it has no income, no activity, or is in bankruptcy. The return is filed on Form 1120, which reports income, deductions, credits, and tax liability.
Filing deadlines
A corporation files by the 15th day of the 4th month after its tax year ends.
- Calendar year → April 15
- Short-year returns → same rule
- Dissolved corporations → 15th day of the 4th month after dissolution
- Fiscal year ending June 30 → 15th day of the 3rd month
These deadlines match IRS rules under §6072(b).
Electronic filing
Corporations that file 10 or more returns of any type during the year must e‑file Form 1120. A corporation may request a hardship waiver by submitting a written request to the IRS. This requirement is based on IRS e‑file regulations under Reg. §301.6011‑2.
Extensions
A corporation may request an automatic extension using Form 7004.
- Standard extension → 6 months
- Fiscal year ending June 30 → 7 months
The extension applies only to filing, not to paying tax.
Payment rules
Corporate tax must be paid in full by the original due date. All federal tax deposits—including income tax, payroll taxes, and excise taxes—must be made through EFTPS.
Penalties
Penalties apply unless the corporation shows reasonable cause.
Failure to file
- 5% per month of unpaid tax, up to 25%
- Fraudulent failure → 15% per month, up to 75%
- Minimum penalty for returns over 60 days late → lesser of tax due or $525
Failure to pay
- 0.5% per month, up to 25%
- If both penalties apply, the failure‑to‑file penalty is reduced by the failure‑to‑pay penalty for the same period
Interest accrues on any unpaid tax from the original due date, even if an extension is granted.
Estimated tax payments
A corporation must make estimated payments if it expects to owe $500 or more for the year. Installments are due on the 15th day of the 4th, 6th, 9th, and 12th months.
Regular method
Required annual payment is the lesser of:
- 100% of current‑year tax
- 100% of prior‑year tax (if a full 12‑month return with positive tax)
Large corporations (taxable income ≥ $1 million in any of the prior three years) cannot use the prior‑year safe harbor except for the first installment.
Other methods
Corporations with uneven income may use:
- Annualized income installment method
- Seasonal installment method
Quick refund of estimated tax
A corporation that overpays estimated tax may request a quick refund using Form 4466 if:
- Overpayment ≥ 10% of expected tax, and
- Overpayment ≥ $500
Form 4466 must be filed:
- Before the 16th day of the 4th month after year‑end
- Before filing Form 1120
- Not before the tax year ends
The IRS must act within 45 days.
Summary
Form 1120 rules require corporations to:
- File annually
- Pay tax by the original due date
- Make estimated payments if tax ≥ $500
- Use EFTPS for deposits
- File Form 7004 for extensions
- Follow strict penalty rules
- Use Form 4466 for quick refunds
These requirements come directly from IRS.gov, Form 1120 instructions, Form 7004 instructions, and IRC §§ 6011, 6072, 6651, and 6655.