Penalty and interest calculators

S corporation penalty and interest calculator

A late Form 1120-S costs a monthly penalty for every shareholder, whether or not any tax is due. Enter the number of shareholders and the dates to see it, then add any tax the corporation itself owes.

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, per shareholder: the number of shareholders times the monthly amount times the months late (part of a month counts), capped at 12 months.
Entity-level tax: built-in gains tax or excess passive income tax gets the usual 5% late-filing and 0.5% late-payment penalties, plus daily interest at the IRS rate.
Estimated tax: the Form 2220 test, using the large-corporation rule when it applies.

Need the relief request written? We prepare reasonable-cause and first-time abatement requests. Book a 10-minute call.

Common questions

Is the penalty charged when the S corporation owes no tax?

Yes. It depends on the number of shareholders and months late, not on tax due. The IRS can abate it for reasonable cause, and a small S corporation may qualify for first-time relief.

How many months does the penalty run?

For each month or part of a month the return is late or incomplete, up to 12 months. For returns due in 2026 the amount is $255 per shareholder per month.

What other penalties can come with it?

A late or missing Schedule K-1 carries its own penalty, $340 per schedule for returns due in 2026. The calculator notes this but does not add it.

Official sources

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