When an amended federal return shows you owe more tax, the late payment penalties on amended returns run from the original April 15 due date, not from the day you file Form 1040-X. The failure-to-pay penalty is 0.5% of the unpaid tax per month, capped at 25%, and daily compounding interest accrues on top at a rate currently set at 6% a year for individual underpayments. Both charges run at the same time, so every month you delay makes the correction more expensive.
How the Failure to Pay Penalty Is Calculated
The IRS treats any additional tax on your amended return as if it was owed on the original filing deadline for that tax year. For most individuals, that’s April 15 of the year after the tax year.1Internal Revenue Service. When to File An extension moves your filing deadline but never your payment deadline, so the penalty clock started the day after that April date.
The rate is 0.5% of the unpaid tax for each month or partial month the balance stays outstanding.2Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax A partial month counts the same as a full one. One day into a new month adds another 0.5%. The penalty tops out at 25% of the unpaid amount, which is reached at roughly 50 months.
If you enter into a formal installment agreement with the IRS, the monthly rate drops to 0.25% for any month the agreement is active, provided your original return was filed on time (including extensions).2Office of the Law Revision Counsel. 26 USC 6651 – Failure to File Tax Return or to Pay Tax The 25% ceiling still applies; it just takes longer to reach.
One penalty you don’t have to worry about here is the failure-to-file penalty. It’s 5% per month, but only applies when a return wasn’t filed on time. Because you’re amending a return you already filed, only the failure-to-pay side is in play.
How Interest Adds Up on Top
Interest is charged separately from the penalty. The IRS sets the rate by taking the federal short-term rate and adding three percentage points, and it adjusts every quarter.3Internal Revenue Service. Topic No. 653 – IRS Notices and Bills, Penalties and Interest Charges For the quarter beginning April 1, 2026, the individual underpayment rate is 6%.4Internal Revenue Service. Internal Revenue Bulletin: 2026-08
Interest compounds daily. Each day’s interest is added to the balance, and the next day’s calculation runs on the slightly higher figure.3Internal Revenue Service. Topic No. 653 – IRS Notices and Bills, Penalties and Interest Charges Over a few months the effect is small. Over several years it becomes significant.
Interest is almost never waived. Even if you get the failure-to-pay penalty removed through one of the options below, the interest stays. The narrow exception is when an IRS error caused the delay. For most amended-return situations, expect to pay the full interest amount.
When a 20% Accuracy Penalty Also Applies
An accuracy-related penalty of 20% of the underpayment can be added if the original mistake involved negligence or a substantial understatement of tax. Negligence means you didn’t make a reasonable attempt to follow the rules, or you carelessly or intentionally ignored them. Substantial understatement, for individuals, means the original return understated tax by the greater of 10% of the correct tax or $5,000. If the qualified business income deduction was involved, the threshold drops to 5% of the correct tax or $5,000.5Internal Revenue Service. Accuracy-Related Penalty
Filing an amended return on your own can help. Catching and correcting the mistake yourself shows good faith and weakens a negligence argument. It doesn’t automatically block the substantial understatement penalty when the dollar thresholds are met. You can argue reasonable cause and good faith for the original position, but the burden of showing it is on you.
Pay the Additional Tax When You File Form 1040-X
The single most effective way to limit what you owe is to pay the additional tax at the same time you file Form 1040-X. Penalties and interest keep accruing while the IRS processes your amended return, and processing typically takes 8 to 12 weeks, sometimes 16.6Internal Revenue Service. Amended Return Frequently Asked Questions Waiting for a bill means months of extra charges.
If you file a paper Form 1040-X, you can include a check or money order. You can also pay online through IRS Direct Pay at irs.gov/payments, choosing the 1040 form type and the tax year you’re correcting. Make sure the payment identifies the correct year and Social Security number so it posts to the right account.
Paying immediately stops the penalty and interest from growing on the tax itself. The IRS will then bill you separately for whatever penalty and interest accrued between the original due date and the date your payment posted. That figure is usually much smaller than what would build up while your amended return sits in the queue.
Getting the Penalty Reduced or Removed
Interest is off the table in nearly all cases, but the failure-to-pay penalty can often be reduced or wiped out.
First-Time Abatement
This is the simplest option. The IRS will waive the penalty if you have a clean compliance record for the three tax years before the year at issue: all required returns filed, no penalties assessed (or any prior penalty removed for a reason other than this same waiver).7Internal Revenue Service. Administrative Penalty Relief You also need to have paid the tax or set up a payment arrangement.
Reasonable Cause
If first-time abatement isn’t available, you can argue reasonable cause. The standard is that you exercised ordinary care and prudence but still couldn’t pay on time.8Internal Revenue Service. Penalty Relief Serious illness, a natural disaster, destruction of records, or bad advice from a tax professional can work. The IRS expects specific facts and documentation, not general excuses.
Statutory Exceptions
Some situations get automatic relief by law. The common ones are living in a federally declared disaster area or serving in a combat zone.9Internal Revenue Service. Penalty Relief Due to Statutory Exception These extend deadlines and suspend penalty accrual for the covered period.
How to Ask
You usually request abatement after the IRS assesses the penalty and sends a notice. The fastest route is to call the number on the notice; representatives can approve some requests by phone. If not, submit a written request on Form 843.8Internal Revenue Service. Penalty Relief Don’t hold the tax hostage to the penalty dispute. Pay the tax now, contest the penalty later.
Don’t Forget the State Return
If your federal amendment changes your tax liability, most states with an income tax require an amended state return too. Many states have their own deadline for reporting the federal change, commonly 90 to 120 days after the federal adjustment is finalized, though windows vary. State late payment penalties and interest rates aren’t tied to federal rules and can be steeper. Check your state revenue agency for the notification deadline and filing requirements so you don’t get hit with a second set of charges.