Free 2026 Underpayment Penalty Calculator

1. Enter the required estimated tax payment and what was paid.
2. Enter the number of days the amount may be outstanding.
3. Use the default annual rate or change it after checking current IRS quarterly interest rates.

Subtract payments from the required amount, floor underpayment at zero, then multiply by an annual penalty rate and the days outstanding divided by 365.

A $2,000 underpayment outstanding for 90 days at a 7% annual rate is estimated as $2,000 x 7% x 90/365.

Year scope: Use the year selector or year note on the calculator itself when comparing thresholds, rates, deductions, or credit limits.

This calculator is maintained against official IRS, SSA, and other primary-source guidance where applicable. Review the sources page and editorial methodology page to verify update practices.

Estimate a simplified underpayment penalty from an unpaid amount, days outstanding, and annual IRS-style interest rate. This tool is for planning and safe-harbor awareness, not a replacement for Form 2210.

Estimate only. Actual IRS penalties can require Form 2210 annualized income methods and quarterly rate changes.