What is the IRS failure-to-pay penalty for 2025 taxes?

The IRS failure-to-pay (FTP) penalty is 0.5% per month on unpaid tax, up to a maximum of 25%. It begins accruing April 16, 2026. If you filed Form 4868 and paid at least 90% by April 15, 2026, the penalty is waived for the extension period.

What is the IRS underpayment rate for Q2 2026?

Per Rev. Rul. 2026-5 (IRS IRB 2026-8, February 17, 2026), the individual underpayment rate is 6% per year for Q2 2026, compounded daily under IRC 6622, down from 7% in Q1 2026.

Does a Form 4868 extension eliminate the failure-to-pay penalty?

No. Form 4868 extends time to file, not to pay. Tax is still due April 15, 2026. However, if you filed the extension AND paid at least 90% by April 15, the FTP penalty is waived. Interest still accrues on any unpaid balance.

If I owe $100,000 and pay October 15, 2026, how much extra do I owe?

With nothing paid by April 15: FTP penalty ~$3,000 (0.5% x 6 months); interest on tax ~$3,054 (6% daily compound, 183 days); interest on penalty ~$38. Total extra ~$6,092.

2025 IRS Penalty & Interest Calculator | Karla CPA

⚖️ 2025 Tax Year

IRS Penalty & Interest Calculator

Calculate your exact failure-to-pay penalty and daily-compounded interest if you filed a Form 4868 extension and are paying your 2025 tax bill after April 15, 2026.

Tax Information

Total Tax Liability (Line 24) ?Your total 2025 federal income tax from Line 24 of Form 1040.

Amount Paid by April 15, 2026 ?All withholding + estimated payments + any extension payment made on or before 4/15/2026.

✓ ≥90% paid by April 15 — FTP penalty waived under extension safe harbor

Final Payment Date

Extension deadline: October 15, 2026

Filed a timely Form 4868 extension

Extension grants extra time to file, not to pay. FTP penalty still accrues unless ≥90% was paid by 4/15.

IRS Quarterly Rates §6621

Editable

Q2 2026 confirmed at 6% per Rev. Rul. 2026-5 (IRB 2026-8, Feb 17 2026). Q3/Q4 assumed same until officially announced.

Q2 2026 — Apr 1–Jun 30

Q3 2026 — Jul 1–Sep 30

Q4 2026 — Oct 1–Dec 31

Payments After April 15

Each payment reduces the principal on that date, cutting future interest.

No additional payments added.

Total Due on Payment Date

$0.00

Extra Cost (P&I)

Unpaid at 4/15

FTP Penalty

$0.00

Interest on Tax

$0.00

Interest on Penalty

$0.00

Per IRC §6601

Total P&I

$0.00

All extra costs

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Quarter-by-Quarter Interest Breakdown

Period	Days	Rate	Opening	Interest	Closing

Month-by-Month FTP Penalty Interest

Month	Assessed	Chunk	Days	Interest

About This IRS Penalty Calculator

This free tool calculates the IRS failure-to-pay penalty under IRC §6651 and daily-compounded underpayment interest under IRC §6622 for individuals who filed a Form 4868 extension on their 2025 Form 1040 and are paying their remaining balance after April 15, 2026.

The Q2 2026 individual underpayment rate of 6% is confirmed per Rev. Rul. 2026-5, published in IRS Internal Revenue Bulletin 2026-8 on February 17, 2026. Q3 and Q4 2026 IRS underpayment rates are assumed at 6%; official rates are announced quarterly. Results may differ from IRS notices due to rounding, additional penalties, or rate changes.

Have questions about your specific tax situation? Contact us for personalized guidance.

DISCLAIMER: This calculator is provided for estimation purposes only and does not constitute professional tax advice.

IRS Penalty & Interest Calculator

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