Penalty and interest calculators

C corporation penalty and interest calculator

Enter the tax, the due date and the dates you filed and paid to see the Form 1120 penalties and interest, and test the corporation's estimated tax payments against the Form 2220 rules.

Estimates for 2026. Written by Prem Tax and Accounting Corp, a CPA firm. The calculators follow the published federal rules and the state rules we checked, and nothing you type leaves your browser. The IRS or state notice is the official amount, and relief such as first-time penalty abatement or reasonable cause can lower it. This is general information, not tax advice.

Prepared by Prem Tax and Accounting Corp. Last checked against official sources on November 11, 2026.

An estimate, not an IRS bill. The figures follow the federal rules and rates explained on this page. Relief such as first-time penalty abatement or reasonable cause can reduce penalties, and the notice you receive is the official amount.

How the estimate works

Late filing and late payment: 5% and 0.5% a month with the same caps and offset as for individuals, plus daily interest at the IRS underpayment rate.
Estimated tax: the Form 2220 regular method, with the $500 threshold and the large-corporation rule.

We prepare corporate returns and respond to IRS penalty notices. Book a 10-minute call.

Common questions

When is a calendar-year Form 1120 due?

April 15 for a calendar-year corporation, or the 15th day of the fourth month after the year ends for a fiscal year. Form 7004 gives an automatic extension to file, not to pay.

What is the large corporation rate?

Interest on a large corporate underpayment, a balance over $100,000, runs 2 points above the normal underpayment rate from the 30th day after the first notice.

What is the minimum late-filing penalty?

For a return due in 2026 and filed more than 60 days late, the smaller of $525 or 100% of the tax.

Official sources

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