IRS Code 6651: Failure to File and Failure to Pay Penalties Explained

If you've received an IRS notice that references Section 6651, you're looking at the part of the tax code that imposes penalties for filing a return late or paying taxes late. For many U.S. taxpayers—especially anyone trying to make sense of an IRS letter without a tax or legal background—that can mean a failure-to-file penalty of 5% per month, up to 25%, and a failure-to-pay penalty of 0.5% per month, also based on unpaid tax.

This guide explains what IRS Code 6651 means, how those penalties are calculated and assessed, when key deadlines apply, how Section 6651 interacts with other IRS penalties, and what relief options, including penalty abatement, may be available. Knowing how this section works can help you respond to an IRS notice faster, avoid added charges, and decide what to do next.

Quick Answer: What Is IRS Code 6651?

Internal Revenue Code Section 6651 governs penalties for failing to file or pay taxes on time. It authorizes the IRS to impose additions to tax when a taxpayer misses a filing deadline, doesn't pay the tax shown on a return, or both.

Here's a quick breakdown of the three main penalty types under this section:

• Failure to file penalty – 5% of unpaid tax per month (or fraction thereof) you're late, up to 25%. This is the late filing penalty.

• Failure to pay penalty – 0.5% of unpaid tax per month, up to 25%. This applies when you file on time but don't pay tax in full.

• How they differ from interest – Interest compounds daily on unpaid taxes and penalties until paid in full. Interest is not a penalty-it's a separate charge that runs on top of any assessed penalties.

Example: Suppose you owe $10,000 on your 2025 individual income tax return. You miss the April 15 due date, don't request an extension, and file three months late without paying. You'd face roughly $1,350 in failure to file penalties plus $150 in failure to pay penalties-over $1,500 in additions to tax before interest even enters the picture.

ClearNotice helps taxpayers understand IRS letters that reference IRC § 6651, including key deadlines and required next steps. ClearNotice does not replace a CPA or attorney.

Overview of IRS Code 6651 and Related Penalties

IRC § 6651 is the primary "delinquency" penalty provision in the Internal Revenue Code. It covers three scenarios: failure to file a required tax return, failure to pay the tax shown on that return, and fraudulent failure to file.

These IRS penalties commonly show up on balance-due notices such as the CP14, CP501, CP503, CP504, and Letter 1058/LT11. If you've received one of these, there's a good chance Section 6651 is cited somewhere on the page.

It's worth understanding where § 6651 fits among other civil penalties:

The IRS penalty handbook-formally the Internal Revenue Manual Part 20.1-guides IRS employees in computing, assessing, and abating § 6651 tax penalties. The penalty applies to any type of unpaid tax, not just income tax.

Failure to File Penalty – IRC § 6651(a)(1)

The failure to file penalty kicks in when an income tax return-Form 1040, 1041, 1120, or similar-isn't filed by the date prescribed for filing. For most individual returns, the original due date is April 15 (or the next business day). A valid extension under § 6081 pushes the filing deadline to October 15, but that only extends the time to file, not the time to pay.

This distinction matters: you can avoid the failure to file penalty even if you can't fully pay tax, simply by submitting your return (or a timely extension) before the deadline. Late filing is one of the most expensive IRS penalties and can quickly dwarf the failure to pay amount.

If a taxpayer fails to timely file their return and cannot demonstrate reasonable cause, the penalty imposed is mandatory.

How the Failure to File Penalty Is Calculated

The failure-to-file penalty is 5% of the unpaid tax per month, up to a maximum penalty of 25%. Each month-or fraction thereof-that the return filed arrives after the due date triggers another 5% charge.

The penalty amount is based on the net amount due: the tax required to be shown on the return minus any payments or credits applied as of the original due date. Withholding and estimated tax payments reduce the base.

The penalty period begins the day after the due date. For a 2025 Form 1040 due April 15, 2026, failure continues starting April 16.

Example:

After five months, the penalty maxes out at 25% of the unpaid tax-$2,500 on a $10,000 tax balance.

Minimum Failure to File Penalty After 60 Days

If a return is filed more than 60 days after the original due date, a minimum penalty applies under § 6651(a)(1). Historically, if a return is over 60 days late, the minimum penalty is the lesser of $435 or 100% of unpaid tax. The IRS adjusts this figure for inflation annually-for returns due in 2025, it was $510, and for returns due in 2026, it is $525.

How the minimum works in practice: Suppose you owe only $300 in tax and file 90 days late. The minimum is the lesser of $525 or 100% of the $300 tax balance. Since $300 is less, your minimum penalty is $300.

This minimum does not apply if the taxpayer demonstrates that the late filing was due to reasonable cause and not willful neglect.

Failure to Pay Penalty – IRC § 6651(a)(2)

The failure to pay penalty applies when the tax shown on a timely filed return isn't paid by the due date. This penalty is separate from the failure to file penalty-it focuses entirely on the unpaid balance.

The failure-to-pay penalty is 0.5% per month of the unpaid tax, up to a maximum amount of 25%. The late payment penalty is 0.5% of unpaid tax monthly regardless of the type of return.

A similar penalty under § 6651(a)(3) applies when the IRS assesses additional tax after an audit or files a substitute for return and the taxpayer doesn't pay after receiving a first notice and demand.

The maximum penalty for late payment is 25% of unpaid taxes. This is the penalty most often shown on notices for people who filed on time but could not fully pay tax owed.

How the Failure to Pay Penalty Is Calculated and Coordinated

The standard rate is 0.5% of unpaid tax per month or fraction thereof. But the rate shifts depending on the situation:

• After a levy notice: The penalty increases to 1% per month once the IRS sends a written notice of intent to levy (such as a CP504 or Letter 1058) and 10 days pass without payment.

• During an installment agreement: If you've filed on time and entered a qualifying payment plan under § 6159, the rate drops to 0.25% per month.

Combined penalty rule: When both failure to file and failure to pay penalties apply in the same month, the total penalty is reduced to 5%. The failure to file portion drops from 5% to 4.5%, and the failure to pay portion remains at 0.5%.

Here's what that looks like over five months for a taxpayer who both filed and paid late on a $10,000 tax debt:

After month 5, the FTF caps out (22.5% total). But the FTP penalty continues accruing at 0.5% until you pay or hit the 25% ceiling-meaning the combined maximum penalty exposure is 47.5% of the original balance, before interest.

Fraudulent Failure to File – IRC § 6651(f)

Fraudulent failure to file is a far more severe penalty provision. It applies when the IRS determines that a taxpayer's failure to file was willful and intended to evade tax-not merely negligent or forgetful.

Fraudulent failure to file incurs a penalty of 15% per month, with a maximum penalty of 75% of the unpaid tax. That's triple the normal rate and triple the cap.

The IRS bears the burden to prove fraud by clear and convincing evidence. Common "badges of fraud" include concealment of income, destruction of records, cash dealings with no paper trail, and inconsistent explanations. Simple late filing or even carelessness is not enough to meet the standard.

If you receive a notice alleging fraudulent failure, seek legal counsel immediately. These penalty provisions often run parallel to potential criminal exposure, and the stakes extend well beyond civil penalties.

Period Subject to IRC 6651 Penalties and Key Dates

Understanding the period subject to these penalties is critical for verifying your notice is correct.

• Failure to file: The penalty period begins the day after the latest applicable due date. That could be the original due date, the extended due date if you filed a timely extension, or a postponed due date under disaster relief (§ 7508A) or combat zone rules (§ 7508).

• Failure to pay: This penalty runs from the day after the original due date-typically April 16 for individual returns-even if you obtained a valid extension to file in October. Extensions don't extend the time to pay.

• Disaster and combat zone relief: Declared disasters and combat zone service can suspend the running of these penalties for specified periods.

The IRS can assess this penalty at any time, and in certain fraud situations, the IRS can assess penalties at any time without a statute of limitations that would normally restrict assessments. Taxpayers should use IRS transcripts or notices decoded by ClearNotice to verify the exact penalty start and stop dates for each tax year and fiscal year involved.

Interaction with Estimated Taxes, Deposits, and Other IRS Penalties

Section 6651 is not the only penalty provision you might see on an IRS notice. Here's how it relates to other common penalties:

• Estimated tax penalties: Underpayment of estimated taxes is penalized under § 6654 for individuals and § 6655 for corporations-not § 6651. If you didn't make enough taxes in estimated tax payments during the year, the underpayment penalty (sometimes called an estimated tax penalty) appears as a separate line item. This is distinct from the failure to pay penalties under § 6651.

• Deposit penalty: Failure to deposit employment taxes falls under § 6656 and uses its own tiered rate structure (2%, 5%, 10%, or 15% depending on how late the deposit is). Information return penalties under § 6721/6722 are also separate.

• Accuracy penalties: Sections 6662 and 6663 address negligence, substantial understatement, and civil fraud on filed returns-a different issue from filing or paying late.

These penalties can stack. A single IRS account might show a late filing penalty under § 6651(a)(1), an estimated tax penalty under § 6654, and accuracy penalties under § 6662, all for the same tax year. Review your notices carefully-or upload them to ClearNotice through our IRS estimated tax penalties guide-to see exactly which code sections apply.

Reasonable Cause, Penalty Abatement, and First-Time Relief

Penalties may be waived if due to reasonable cause and not willful neglect. The IRS allows reasonable cause defenses for penalties, and taxpayers can assert reasonable cause for various circumstances-it is not limited to a single type of hardship.

Common reasonable cause situations recognized in the IRS penalty handbook include:

• Serious illness or hospitalization of the taxpayer or immediate family member

• Death in the family

• Natural disaster, fire, or casualty that destroyed records

• Inability to obtain necessary and accurate information despite exercised ordinary business care

• Reliance on an adviser's judgment where the taxpayer provided sufficient expertise and information to justify reliance on a competent professional

Financial hardship can be a defense against penalties, and undue hardship must be shown to qualify for penalty relief in payment-related cases. The taxpayer must demonstrate they exercised ordinary business care and prudence but still could not comply.

First Time Abate (FTA): The first-time abate policy can remove penalties for compliant taxpayers who have no similar penalty in the prior three tax years and have filed all required returns. This administrative relief commonly applies to failure to file and failure to pay penalties. You can learn more through our First Time Abate Relief guide.

Penalty abatement requests can be made by phone (call the number on your notice) or in writing. In some cases, the IRS has introduced automatic relief programs-most recently, the Automatic Exemption from Penalty (AEP) program launched in July 2026, which automatically grants relief to eligible taxpayers and is set to replace FTA for returns due on or after January 1, 2027.

If the IRS denies your request, you may be able to appeal administratively or petition the Tax Court for review of the penalty removed or sustained. A penalty removed through reasonable cause or FTA stops further accrual on that specific addition to tax.

How IRS Code 6651 Appears on IRS Notices and How ClearNotice Helps

On common IRS letters, § 6651 penalties are typically labeled with language like "Failure-to-file penalty (IRC 6651(a)(1))" or "Failure-to-pay penalty (IRC 6651(a)(2))." The notice usually shows:

• The penalty amount

• The period subject to the penalty (start and end dates)

• An "as of" date through which penalties and interest have accrued

• The applicable interest rate on the balance

This information isn't always presented in plain English. Terms like "addition to tax," "net amount due," and "notice and demand" can obscure what's actually happening with your account.

ClearNotice's service lets taxpayers upload a CP notice or letter and automatically identifies references to IRC § 6651. The platform explains:

• What triggered the penalty (late filing, late payment, or both)

• Whether it's a failure to file, failure to pay, or fraudulent failure penalty

• Key deadlines for response or payment

• Whether the notice is a first notice or an escalation toward enforcement

What to do next: Act quickly. Every month of delay means more penalties and interest. File any missing returns (even without full payment), pay what you can to reduce the base the penalty applies against, consider an installment agreement if you can't pay in full, and explore penalty abatement options with help from a tax professional. Voluntary compliance-filing and paying before the IRS contacts you-always produces better outcomes than waiting.

Don't let an IRS notice sit unanswered. Upload your letter to ClearNotice today to see exactly which penalties apply, what your deadlines are, and what steps to take next.