Model IRS interest with the compound interest calculator
Approximate daily compounding on an unpaid balance using your principal, rate, and timeline.
Open compound interest calculatorSituation A vs Situation B
Situation A: You owe money. Late filing is expensive. The IRS starts charging penalties immediately and interest compounds daily.
Situation B: You're getting a refund. There is no penalty for filing late. None. The IRS owes you money - they're not going to fine you for taking longer to collect it.
Most people assume late filing is always bad. It's not. But if you're in Situation A and you're thinking of waiting a few more days, the math below might change your mind.
Situation A: You Owe Money - File Now
If you owe taxes and miss the April 15 deadline without filing an extension, two separate penalty clocks start ticking immediately:
1. The Failure-to-File Penalty
This is the big one. 5% of your unpaid tax for every month or partial month your return is late, up to a maximum of 25%. [1]
Partial month means partial month. File one day into May and you've triggered a full month of the penalty. The IRS doesn't prorate. Once 5 months have passed, this penalty maxes out at 25% - but the other charges keep going.
After 60 days: if your return is more than 60 days late, there's also a minimum penalty - the lesser of $525 or 100% of the tax owed. So if you owe $300 and file 61 days late, your minimum penalty is $300. Your entire tax bill, doubled. [1]
2. The Failure-to-Pay Penalty
0.5% per month on any unpaid balance, also up to 25% maximum. [2] This one starts the same day as the failure-to-file penalty and keeps running even after the failure-to-file maxes out at 5 months.
When both penalties apply in the same month, they're combined at a net rate of 5% rather than 5.5% - the failure-to-file penalty is reduced by the 0.5% failure-to-pay amount for that month.
3. Daily Compounding Interest
On top of both penalties, the IRS charges interest on any unpaid balance at the federal short-term rate plus 3% - currently approximately 7% annually - compounded daily. [1] Interest starts the day after the April 15 deadline regardless of whether you filed an extension.
Extensions delay your filing deadline - not your payment deadline
If you owe money and filed Form 4868, you still had to pay by April 15 to avoid interest.
What This Looks Like in Real Numbers
Here's exactly what a $2,000 unpaid tax bill grows to over time if you do nothing:
| Timeline | Failure-to-File Penalty | Failure-to-Pay Penalty | Interest | Total Owed |
|---|---|---|---|---|
| April 15 (deadline) | $0 | $0 | $0 | $2,000 |
| 1 month late (May 15) | $90 | $10 | $12 | $2,112 |
| 2 months late (Jun 15) | $180 | $20 | $25 | $2,225 |
| 3 months late (Jul 15) | $270 | $30 | $38 | $2,338 |
| 5 months late (Sep 15) | $360 | $50 | $62 | $2,472 |
| 12 months late (Apr 26) | $360 | $120 | $146 | $2,626 |
Illustrative example for a fixed $2,000 unpaid balance; actual IRS rates and combined penalty rules may vary. Verify current figures at IRS.gov.
Note: After 5 months, the failure-to-file penalty maxes out at 25% ($500 on a $2k bill - but here reduced slightly due to the combined-month rule). The failure-to-pay penalty keeps running until the 25% cap, and interest compounds daily throughout.
💡 The most important number in this table: at just one month late, your $2,000 bill has already grown to $2,112. That $112 is the IRS charging you for waiting 30 days. A short-term bank loan at 15% APR would cost you $25 for the same month. Filing and borrowing to pay is almost always cheaper than waiting.
What to Do If You Can't Pay the Full Amount
The single most common and costly mistake: not filing because you can't pay. These are two separate things. Filing without paying is significantly better than not filing at all.
File today even if you can't pay. Filing stops the 5% failure-to-file penalty from accumulating. You'll still owe the 0.5% failure-to-pay and daily interest - but the failure-to-file penalty is 10 times larger and you can stop it immediately by submitting your return.
Options for paying what you owe:
- •IRS payment plan (installment agreement): Available online at IRS.gov. If you owe under $50,000 and are up to date on filing, you can set up a monthly payment plan in minutes. The failure-to-pay penalty drops to 0.25% per month while you're on a payment plan. [2]
- •Pay what you can now: Any payment reduces the balance on which penalties and interest accrue. Paying $500 of a $2,000 bill today means tomorrow's interest runs on $1,500, not $2,000.
- •Borrow to pay: At 7% IRS interest plus 5% failure-to-file penalty = effective 12% monthly rate in Month 1. A credit card at 20% APR costs 1.67% per month - still cheaper than the combined IRS charges before the failure-to-file maxes out.
Situation B: You're Getting a Refund - Relax (Within Limits)
If the IRS owes you money, there is no failure-to-file or failure-to-pay penalty for filing late. There can't be - you don't owe anything.
The IRS isn't going to penalise you for taking longer to collect money they owe you. You can file tomorrow, next month, or next year - penalty-free.
The only deadline that matters if you're getting a refund: you have three years from the original filing deadline to claim it. For 2025 tax returns due April 15, 2026, your refund claim window closes April 15, 2029. After that, unclaimed refunds are permanently surrendered to the US Treasury. [3]
📌 The practical advice: if you're getting a refund, file now anyway. Your money is sitting with the IRS earning them interest-free use of your cash. The average 2026 refund is $3,571 - every month you delay is another month that money isn't in your account or invested.
At 4% APY in a high-yield savings account, $3,571 earns roughly $12 per month. That's not a fortune - but it's money you've already earned that belongs to you.
Why Some 2026 Refunds Are Larger - and Why Some People Unexpectedly Owe
Searches for "big beautiful bill", "no tax on overtime", and "no tax on tips" have exploded this week - and for good reason. The One Big Beautiful Bill Act (OBBBA) introduced several new deductions for the 2025 tax year that affect millions of filers:
- •No tax on tips: Tip income is now deductible for eligible workers. If you received tips and didn't adjust your withholding, you may be getting a larger refund than expected.
- •No tax on overtime: Overtime pay now has a deduction for eligible employees. Many workers who earned significant overtime in 2025 are seeing meaningfully larger refunds.
- •Larger standard deduction: The standard deduction increased again for 2025, meaning more income is shielded from tax before itemised deductions.
- •Senior deduction: Taxpayers 65+ can claim an additional $6,000 deduction - one of the largest new OBBBA benefits.
These are the main reasons the average 2026 IRS refund ($3,571) is up 10.9% from last year. If your refund is larger or smaller than expected, the Big Beautiful Bill changes are likely the explanation.
A Note for Gig Workers and Freelancers
Searches for "estimated tax payments 2025" are up 300% this week - a sign that many self-employed workers are realising they should have been making quarterly payments throughout the year.
If you're self-employed, a freelancer, or run a side hustle, the IRS expects quarterly payments - not just year-end filing. Missing those estimated tax payments can result in an underpayment penalty on top of any balance due.
If you owe a large amount today as a gig worker, the same advice applies: file today and pay what you can. Then mark your calendar for 2026 estimated payment dates: June 16, September 15, and January 15, 2027.
The Extension Option - What It Does and Doesn't Do
If you haven't filed yet and you know you can't finish your return by April 15th, filing Form 4868 today gives you until October 15, 2026 to submit your return. This eliminates the failure-to-file penalty entirely during that extension period.
Critical: an extension does not extend your payment deadline. If you owe money, you were still required to pay by April 15. If you're filing an extension today and you owe, you should estimate your bill and pay what you can now to limit further interest accumulation.
Form 4868 is free to file electronically at IRS.gov or through any major tax software. It takes about 10 minutes and is approved automatically - the IRS does not require a reason.
The Decision Framework in 60 Seconds
| Your situation | Action | Why |
|---|---|---|
| You owe money - haven't filed | File today, pay what you can | Stops 5% FTF penalty immediately |
| You owe money - can't pay at all | File anyway + set up payment plan | FTF is 10x worse than FTP |
| Getting a refund - haven't filed | File soon, no rush | Zero penalty, but get your money |
| Filed but didn't pay | Pay now or set up plan | Interest running daily since Apr 15 |
| Need more time to finish return | File Form 4868 today | Buys you until October 15 |
Use HelpCalculate to Model Your Situation
The Compound Interest calculator at HelpCalculate.com can model the daily compounding interest on any unpaid IRS balance. Enter your unpaid amount as the principal, 7% as the annual rate (current approximate IRS rate), and compounded daily - then set the timeline to see exactly what you'll owe at any point. The number updates fast and tends to motivate action.
Key takeaways
- •If you owe: failure-to-file (up to 5%/month) and failure-to-pay (0.5%/month) stack with daily interest - filing stops the larger failure-to-file clock.
- •If you are due a refund: there is no late-filing penalty, but you forfeit the refund after three years if you never file.
- •Form 4868 extends time to file, not time to pay; pay what you can by April 15 to limit interest.
- •OBBBA deductions (tips, overtime, standard deduction, senior deduction) help explain larger 2026 refunds for many filers.
Conclusion
Know which situation you are in - owe versus refund - and act today if you owe.
When in doubt, file. You can always set up a payment plan; you cannot always undo months of failure-to-file penalties.
FAQ
Is there a penalty if I file late but the IRS owes me a refund?
No failure-to-file or failure-to-pay penalty applies when you do not owe tax. You still should file within three years of the original due date to claim your refund.
Does Form 4868 give me more time to pay?
No. It extends the deadline to submit your return, not to pay tax due. Interest (and often failure-to-pay penalties) can still apply to amounts unpaid after April 15.
Cited sources
- IRS - Topic 653, Penalties and InterestFailure-to-file, failure-to-pay, interest, and related rules.
- IRS - Failure to Pay PenaltyRates, installment agreement reduction, and guidance.
- IRS - Topic 308, Refund of amounts withheld or paid as estimated taxTime limits for claiming a refund (generally within three years of the due date).
- Instead.com - Late tax filing penalty rates 2026As cited in source document; verify against IRS primary sources.
Disclaimer: This article is for general informational purposes only and does not constitute tax advice. Consult a qualified tax professional for guidance specific to your situation. Tax law can change - verify current rates at irs.gov.
Related calculators
Related posts
Finance
What To Do With Your Tax Refund in 2026: The Smart, the Dumb, and the Math
Average refunds are up in 2026. Here is how to prioritize debt, investing, and emergency savings - with the math behind each choice.
Finance
The True Cost of Your Mortgage in Year One Will Shock You
How a $400,000 home loan actually works - and what your bank does not lead with. Year-one payment split, hidden costs, amortization crossover, and what one extra payment can save.