IRS Penalty and Interest Calculator: What the IRS Actually Charges You (2026 Rates)
The short answer
The IRS charges on an unpaid $5,000 balance, filed on time, add $54.25 in month one and $672.35 by month twelve, from the failure-to-pay penalty plus 7% daily interest. Filing late costs far more than paying late.
Updated October 2026.
The IRS penalty and interest calculator math in this article shows exactly what an unpaid federal balance costs, month by month. On $5,000 owed and filed on time, the failure-to-pay penalty plus 7% daily interest adds $54.25 in month one and $672.35 by month twelve. Filing late costs far more.
This article is educational information about US federal tax penalties and interest, not tax advice. The rules below cover individual Form 1040 balances. For a large balance, an audit notice, or anything you are unsure about, talk to a qualified tax professional before acting.
What does an IRS penalty and interest calculator show on an unpaid $5,000 balance?
Start with the mildest case: you filed your return on time, you owe $5,000, and you pay nothing yet. Only one penalty applies, the failure-to-pay penalty at 0.5% of the unpaid tax per month. Interest also runs at 7% per year, compounded daily, on the tax plus the penalties as they are assessed (the IRS rate for the quarter starting October 1, 2026, per Revenue Ruling 2026-15).
| Month | Failure-to-pay penalty so far | Balance owed | Extra cost so far |
|---|---|---|---|
| 1 | $25 | $5,054.25 | $54.25 |
| 2 | $50 | $5,108.82 | $108.82 |
| 3 | $75 | $5,163.70 | $163.70 |
| 4 | $100 | $5,218.91 | $218.91 |
| 5 | $125 | $5,274.44 | $274.44 |
| 6 | $150 | $5,330.29 | $330.29 |
| 7 | $175 | $5,386.47 | $386.47 |
| 8 | $200 | $5,442.98 | $442.98 |
| 9 | $225 | $5,499.82 | $499.82 |
| 10 | $250 | $5,557.00 | $557.00 |
| 11 | $275 | $5,614.50 | $614.50 |
| 12 | $300 | $5,672.35 | $672.35 |
Method, in one line: penalty assessed at each month end, interest compounded daily at 7% on the tax and the penalties assessed so far, using an average month of 365/12 days. Your real IRS notice will differ by a few dollars because the IRS counts exact days. The shape is what matters: the bill grows every single day, and the growth speeds up as penalties stack into the interest base.
Notice the split at month 12. Of the $672.35 extra, $300 is penalty and about $372 is interest. People fixate on the penalty, but on a balance left alone for a year, interest quietly becomes the bigger half.
Running this table for your own balance, with your own filing and payment dates, is the job of the IRS Penalty Calculator 2026: enter what you owe and the dates, and it shows your penalty plus interest total for every month, so you know the exact cost of waiting one more month.
Is filing late or paying late worse?
Filing late, and it is not close. The failure-to-file penalty is 5% of the unpaid tax per month. The failure-to-pay penalty is 0.5% per month. Same $5,000 balance, six months:
- Filed on time, paid six months late: payment penalty only, 6 x 0.5% = 3.0%, which is $150.
- Filed six months late: the two penalties combine (the next section explains the math), reaching 25.5% of the balance, which is $1,275.
That is 8.5 times more penalty for the same debt and the same six months, before interest. This is why the first rule of owing the IRS is simple: file on time even if you cannot pay a cent. Filing costs nothing, and it keeps you in the cheap penalty lane. If you already missed a filing deadline, our missed tax extension deadline walkthrough covers the October 15 case step by step.
How do the two penalties stack in the same month?
They do not stack at full strength. In any month when both penalties apply, the filing penalty drops from 5% to 4.5%, so the combined rate is 5% per month, not 5.5%. On $5,000, one combined month costs $250 (4.5% is $225, plus 0.5% is $25), not the $275 a naive stack would suggest.
The caps work the same blended way. The filing component maxes out at 22.5% and the payment component at 25%, so the lifetime combined ceiling is 47.5% of the unpaid tax. A balance left unfiled and unpaid for years can grow by almost half from penalties alone, with interest on top.
What is the $525 minimum penalty trap?
Once a return is more than 60 days late, a minimum failure-to-file penalty applies: the smaller of $525 (for returns required to be filed in 2026) or 100% of the tax due. Percentage math stops mattering.
This trap hits small balances hardest. Owe $600 and file more than 60 days late, and the percentage formula would give a far smaller figure, but the minimum replaces it: you pay $525, which is 87.5% of the entire tax bill. Owe $400, and the 100% cap binds instead, so the minimum penalty is the full $400. If your balance is small and your return is unfiled, the calendar matters more than the amount: file before day 60.
Why does one day into a new month cost a full month of penalty?
Because part of a month counts as a full month, for both penalties. Take an extension filer who owes $5,000 and has not filed. October 16 to October 31 is month one of the combined penalty: 5%, or $250. File on October 31 and that is where it stops. File on November 1 instead, one day later, and month two has started: another $250. One day, $250.
There is no grace period and no pro-rating. When you are near the end of a penalty month, filing today instead of tomorrow is real money.
When does a payment plan beat paying the balance off?
An IRS installment agreement cuts the failure-to-pay penalty from 0.5% to 0.25% per month while the agreement is in effect. On $5,000 still owed, that is $12.50 a month instead of $25. Interest at 7% keeps running either way until the balance is gone. Short-term plans (180 days or less) carry no setup fee; a long-term plan set up online with direct debit costs $29.
The decision rule: a payment plan beats raiding your savings only when the cash you would use is your emergency buffer and losing it would push you onto credit cards at 20% or more. If the money is sitting in a savings account earning 4%, paying the IRS today wins, because it stops both the penalty and the 7% interest at once. If paying today would leave you one car repair away from card debt, take the plan, pay the halved penalty, and keep the buffer. Either way, pay as much as you can today first: every dollar paid now is a dollar that stops accruing both charges.
To stay out of this math next year, the quarterly estimated tax calculator shows what to set aside each quarter so April never produces a surprise balance.
Can the IRS waive these penalties?
Sometimes, and 2026 changed the main route. For 2025 tax-year returns, the IRS replaced the old request-based First-Time Abatement with an Automatic Exemption from Penalty: if you qualify (generally, a clean compliance history for the prior three years), the exemption is applied automatically and no request is needed. The request-based First-Time Abatement still exists for earlier tax years. One limit never changes: interest is not abated, even when penalties are.
Reasonable cause is the other path. Serious illness, a death in the family, destroyed records, or bad advice you relied on can qualify, but you have to ask and document it. It is relief with a bar to clear, not an automatic discount.
What did a 36-day delay cost on an $18,000 balance?
Morkel Financial published a larger worked case: a $78,000 tax bill with $60,000 already paid through withholding, leaving $18,000 unpaid on an extended return. Filed October 15, the total penalty was $540. Filed November 20, about 36 days later, it was $2,340. The delay cost $1,800 in penalties alone, and the figures recompute exactly from the IRS formulas above. Interest runs on top of both numbers.
The lesson scales in both directions. Whatever you owe, the cost of waiting is not the daily interest people imagine. It is the monthly penalty steps, and each step is a full month charged for a single day of delay.
FAQ
Can penalties be removed for reasonable cause? Yes. The IRS can relieve penalties when you show reasonable cause, such as serious illness, a natural disaster, or records destroyed outside your control. You request it, usually with Form 843 or a letter, and you document the facts. Interest is never removed this way.
Do states add their own penalties on top of the federal ones? Usually, yes. Most states run their own late-filing and late-payment penalties and their own interest, on their own rates and deadlines. This article covers federal charges only, so check your state tax agency for the second layer.
How do I get the exact number for my balance? An IRS notice tells you what the IRS has assessed so far, but it does not show what next month adds. A calculator that runs your balance, your filing date, and your payment date through the same formulas in this article does. That forward view, month by month, is what tells you whether paying this week beats paying next month.
Sources
- IRS, Interest rates remain the same for the fourth quarter of 2026 (IR-2026-98). Publisher: Internal Revenue Service. Substantiates the 7% individual underpayment rate, compounded daily, for the quarter beginning October 1, 2026, per Revenue Ruling 2026-15.
- IRS, Collection Procedural Questions 3. Publisher: Internal Revenue Service. Substantiates the combined 5% per month rate when both penalties apply, the 47.5% combined maximum, and the $525 minimum failure-to-file penalty for returns required to be filed in 2026.
- IRS, Failure to file penalty. Publisher: Internal Revenue Service. Substantiates the 5% per month filing penalty, its cap, and the part-month rule.
- IRS, Topic 653, IRS notices and bills, penalties, and interest charges. Publisher: Internal Revenue Service. Substantiates the 0.5% failure-to-pay rate, the 0.25% rate during an installment agreement, and daily-compounded interest.
- IRS, Administrative penalty relief. Publisher: Internal Revenue Service. Substantiates the Automatic Exemption from Penalty for 2025 tax-year returns and that interest is not abated.
- IRS, Online payment agreement application. Publisher: Internal Revenue Service. Substantiates the $0 short-term plan fee and the $29 online direct-debit long-term setup fee.
- Morkel Financial, Missed tax extension deadline. Publisher: Morkel Financial. The $78,000-liability worked example ($540 filed October 15 vs $2,340 filed November 20); arithmetic independently recomputed from IRS formulas.
Educational information, not tax advice. When in doubt, talk to a tax professional.
About Kollaz: Kollaz makes smart financial tools for modern money. This article's companion is the IRS Penalty Calculator 2026: enter your balance and dates, and it computes your exact IRS penalty and interest bill month by month. If you are self-employed, the self-employed tax preparation checklist is the companion guide for staying ahead of these deadlines next year.