IRS Penalty & Interest Calculator 2026 β Late Filing & Payment
Calculate IRS failure-to-file penalty, failure-to-pay penalty, and daily interest charges. See total amount owed with month-by-month accrual breakdown.
$
Amount shown on your tax return as owed %
Federal short-term rate + 3% (~8% in 2026) Usually April 15. With extension: October 15.
Date the full tax balance will be paid
Extension moves FTF deadline to Oct 15
$0
TOTAL OWED (Tax + Penalties + Interest)
$0
Failure-to-File Penalty
$0
Failure-to-Pay Penalty
$0
Interest Charges
Penalty & Interest Breakdown
Month-by-Month Accrual
| Month | FTF Penalty | FTP Penalty | Interest | Running Total |
|---|
How IRS Penalties and Interest Work
When you fail to file your tax return or pay taxes owed by the due date, the IRS charges three types of additional amounts: the failure-to-file penalty, the failure-to-pay penalty, and interest. These can compound quickly β a $5,000 tax bill can grow to over $7,000 after 6 months of penalties and interest.
The most important thing to know: filing an extension only eliminates the failure-to-file penalty, not the failure-to-pay penalty or interest. You must still pay your estimated tax by April 15. Even paying 90% of what you owe by April 15 significantly reduces FTP penalties.
The Formula
Failure-to-File: 5% Γ unpaid tax Γ months late (max 25%)
β If both FTF and FTP apply: FTF rate reduced to 4.5% per month
β If >60 days late: minimum FTF = lesser of $510 or 100% of tax owed
Failure-to-Pay: 0.5% Γ unpaid tax Γ months late (max 25%)
Interest: (tax + penalties) Γ daily rate, compounded daily
Daily rate = (1 + annual rate / 365) β 1
Annual rate = Federal short-term rate + 3% (β8% in 2026)
β If both FTF and FTP apply: FTF rate reduced to 4.5% per month
β If >60 days late: minimum FTF = lesser of $510 or 100% of tax owed
Failure-to-Pay: 0.5% Γ unpaid tax Γ months late (max 25%)
Interest: (tax + penalties) Γ daily rate, compounded daily
Daily rate = (1 + annual rate / 365) β 1
Annual rate = Federal short-term rate + 3% (β8% in 2026)
Example
$5,000 owed, filed and paid 6 months late (October 15), no extension:
FTF penalty: 5% Γ $5,000 Γ 5 months (reduced by FTP) = $4.5%/mo β $1,125
FTP penalty: 0.5% Γ $5,000 Γ 6 months = $150
FTF capped check: 5 months Γ 4.5% + 1 month extra FTP = at least 25% max applies
Interest: ~$200 (8% on $5,000 Γ ~183 days)
Total: $5,000 + ~$1,300 + ~$200 = ~$6,500
Penalty as % of original tax: ~30%
FTF penalty: 5% Γ $5,000 Γ 5 months (reduced by FTP) = $4.5%/mo β $1,125
FTP penalty: 0.5% Γ $5,000 Γ 6 months = $150
FTF capped check: 5 months Γ 4.5% + 1 month extra FTP = at least 25% max applies
Interest: ~$200 (8% on $5,000 Γ ~183 days)
Total: $5,000 + ~$1,300 + ~$200 = ~$6,500
Penalty as % of original tax: ~30%
Extended
Payment Timing Analysis
See total cost of your tax debt at different payment dates β understand how delay compounds
See how total cost grows at different payment dates. Every month of delay adds more β this table shows the true cost of procrastination.
| Payment Scenario | Days Late | FTF Penalty | FTP Penalty | Interest | Total Owed | Extra Cost |
|---|
Cost of Waiting
Frequently Asked Questions
What is the IRS failure-to-file penalty?
The failure-to-file (FTF) penalty is 5% of unpaid taxes for each month (or part of a month) your return is late, up to a maximum of 25% of the unpaid tax. If your return is more than 60 days late, the minimum penalty is the lesser of $510 (2026) or 100% of the unpaid tax. Filing an extension (Form 4868) moves your filing deadline to October 15 and eliminates the FTF penalty for that period β but it does NOT extend your time to pay.
What is the IRS failure-to-pay penalty?
The failure-to-pay (FTP) penalty is 0.5% of unpaid taxes per month (or part of a month), up to a maximum of 25%. If both FTF and FTP penalties apply in the same month, the FTF penalty is reduced by the FTP amount (so you pay 5% FTF β 0.5% FTP = 4.5% combined for that month). The FTP penalty continues even after you file your return, until the tax is fully paid.
How does IRS interest work on unpaid taxes?
IRS interest is based on the federal short-term rate plus 3%, compounded daily. For 2026, this is approximately 7β8% annually. Interest accrues from the original due date (April 15) on any unpaid tax balance, including penalties. Interest is not capped and continues to accrue until the full balance is paid. Unlike penalties, interest cannot be waived unless the IRS made an error.
Does a tax extension eliminate all penalties?
An extension (Form 4868) eliminates only the failure-to-file penalty by moving your filing deadline to October 15. It does not extend the time to pay β any tax owed was still due on April 15. If you owe tax and file an extension without paying, the failure-to-pay penalty (0.5%/month) and interest begin immediately on April 15. To minimize penalties, pay as much as possible by April 15 even if you cannot file yet.
Can IRS penalties be reduced or removed?
Yes. The IRS offers penalty abatement in several situations: (1) First-time abatement β if you have a clean compliance history (no penalties in the past 3 years), you may qualify for automatic abatement of FTF and FTP penalties; (2) Reasonable cause β if you can show the failure was due to circumstances beyond your control (serious illness, natural disaster, reliance on incorrect professional advice); (3) Statutory exceptions β certain legal exceptions apply. Interest can only be reduced if there was an IRS error or an "undue delay" by the IRS.