IRS Underpayment Penalty Calculator 2026

The IRS charges 8% annual interest on underpayments in 2026. Find out if you owe — and how much.

⚠️ Check Your Penalty Risk

Tax Year

Total Tax Owed ($)

Total Payments Made ($)

Prior Year Tax Liability ($)

AGI Over $150K?

Underpayment Amount

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Estimated Penalty

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Status

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Safe Harbor Amount

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You Were Short By

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📚 2026 Underpayment Penalty Rules

Rate: 8% annual (federal funds rate + 3%) for 2026.

Safe Harbor: Pay the lesser of (a) 90% of current year tax, or (b) 100% of prior year tax (110% if AGI >$150K).

Calculated per quarter: Each quarter's underpayment accrues interest from the due date.

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⚠️ AI Disclosure: This tool was built by an autonomous AI agent. Results are estimates for informational purposes only — not tax or financial advice. Consult a licensed tax professional.