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When a tax balance goes unpaid, the IRS does not simply hold the number steady while collection proceedings unfold. Interest begins accruing the day after the original filing deadline, it compounds every single day, and it applies not just to the unpaid tax but to any penalties already assessed on top of that tax. A balance that looked manageable in April looks materially different by the following spring, and most taxpayers do not understand why until they receive a notice.
This post explains how IRS interest works, what the current rates are, and what can realistically be done to limit it.
Key Takeaways
- IRS interest on unpaid taxes is authorized under IRC § 6601 and compounds daily under IRC § 6622.
- The underpayment rate for individuals is the federal short-term rate plus 3 percentage points, reset each calendar quarter under IRC § 6621.
- For 2026: Q1 (Jan–Mar) was 7%, Q2 (Apr–Jun) was 6%, Q3 (Jul–Sep) is 7%, per IRS Internal Revenue Bulletins 2025-48, 2026-08, and 2026-22.
- Interest runs on the full balance, unpaid tax plus assessed penalties, until paid in full.
- Unlike most penalties, interest on the underlying tax is almost never waived. Resolving the balance is the only reliable way to stop it.
Why the IRS Charges Interest
The authority for IRS interest comes from IRC § 6601, which requires the IRS to charge interest on any unpaid tax from the date it was due. The statutory rationale is straightforward: money owed to the government but not paid represents a benefit to the taxpayer and a cost to the Treasury. Interest removes that benefit. It is not a punishment for bad behavior. It is compensation for the time value of money, which is why it accrues regardless of whether the taxpayer had good reasons for not paying.
That framing matters in practice. Taxpayers who successfully obtain penalty abatement, either through first-time abatement or reasonable cause, sometimes expect the interest to disappear as well. It usually does not. When a penalty is reduced or removed, the interest that had accrued on that penalty disappears with it. But interest on the underlying tax itself is a different story. The IRS has narrow authority to abate it, and the standard is high.
How the Rate Is Set
Under IRC § 6621(a)(2), the underpayment rate for individuals is the federal short-term rate plus 3 percentage points. The IRS reviews the federal short-term rate each quarter and publishes the resulting interest rate in the Internal Revenue Bulletin. The rate can change from one quarter to the next, which means a balance carried across multiple quarters accrues at different rates depending on when it was owed.
For 2026, those rates are:
- Q1 (January through March): 7% — IRB 2025-48
- Q2 (April through June): 6% — IRB 2026-08
- Q3 (July through September): 7% — IRB 2026-22
Large corporate underpayments carry a higher rate under IRC § 6621(c), currently 9% for Q3 2026, but that category does not affect individual taxpayers.
Daily Compounding: What It Actually Means
The rate published each quarter is an annual rate. Under IRC § 6622, the IRS compounds interest daily. Each day’s interest is calculated on the prior day’s balance plus the prior day’s interest. The result is that the effective annual rate is slightly higher than the stated annual rate.
At 7% compounded daily, the effective annual rate is approximately 7.25%. On a $50,000 balance, that difference is not trivial over a year or two.
More practically, daily compounding means the balance never holds still. Every day the debt sits unresolved, the interest base grows slightly larger, and the next day’s charge is calculated on that larger number. A taxpayer waiting on a collection alternative to close, whether an installment agreement, an OIC, or a CDP hearing, is accumulating interest throughout that wait, even if enforcement is paused.
Interest on Penalties, Not Just Tax
One of the more consequential and least understood features of IRS interest is that it applies to assessed penalties as well as to the underlying tax.
Under IRC § 6601(e)(2)(B), interest accrues on failure-to-file and failure-to-pay penalties from the date those penalties are assessed. A taxpayer who filed late and paid late is accruing interest on two separate penalty amounts in addition to the tax itself. The running balance at any given point is: unpaid tax, plus accrued interest on the tax, plus the assessed failure-to-file penalty, plus interest on that penalty, plus the assessed failure-to-pay penalty, plus interest on that penalty. These components accumulate independently and do not simplify into a single clean number until the balance is fully resolved.
This is one reason the IRS account transcript is the only reliable source of truth on what is actually owed. Notices often reflect a snapshot that is already stale by the time they arrive in the mail.
When Interest Can Be Reduced
Interest on the underlying tax is almost never abated. The IRS has authority under IRC § 6404(e) to abate interest only when it results from IRS errors or delays, a specific documented failure by the IRS to act in a timely or correct manner. These situations are uncommon, and the taxpayer bears the burden of establishing them.
What does work for reducing the total interest burden:
Removing the underlying penalty. When a penalty is abated through first-time abatement or a reasonable cause argument, the interest that had accrued on that penalty disappears with it. The tax interest remains, but the penalty stack shrinks.
Paying the balance faster. There is no substitute for this. Every day the balance is open, interest runs. An installment agreement that runs over 72 months will produce significantly more interest than a lump-sum resolution in month 6. When evaluating payment options, the interest cost of delay is a real factor in the calculation.
Offer in Compromise. A successfully negotiated OIC eliminates the underlying tax balance and all accrued interest and penalties as of the acceptance date. This is part of why OIC negotiations carry urgency. The Reasonable Collection Potential calculation used to evaluate the offer does not freeze the clock while the application is pending. Interest continues to accrue throughout a prolonged application process, and that can affect what the IRS is willing to accept.
The Installment Agreement Reality
Taxpayers who enter installment agreements often assume the interest problem is solved once the agreement is in place. It is not. An installment agreement stops enforcement, no levies, no garnishments. It does not stop interest. The IRS continues to charge interest on the unpaid balance throughout the life of the agreement at whatever rate applies each quarter.
For a large balance paid over several years, the total interest cost is substantial. A $100,000 balance at 7% compounded daily, paid over 60 months in equal installments, generates roughly $19,000 in interest costs over the life of the agreement. That figure rises if rates increase.
This is not an argument against installment agreements. They are the right tool in many situations. It is an argument for understanding what the agreement actually costs and whether a faster resolution path exists.
What to Do If a Balance Is Accruing
The single most effective way to stop interest is to resolve the balance. The fastest path available, whether full payment, a structured payment arrangement, an OIC, or a currently not collectible determination, is the one that minimizes interest cost. The choice among those options depends on the taxpayer’s financial position, the age of the liability, the underlying tax years, and whether penalty abatement is viable.
If a balance has been open for more than a year, an IRS account transcript will show the current total more accurately than any prior notice. That transcript is the starting point for any resolution discussion.
If you are carrying an IRS balance and have not evaluated your resolution options, the interest clock is running regardless. Contact our firm to understand what the actual number is and what it would take to stop it.
Matt Wildes, JD | CLAW Tax Group / Wildes At Law
Schedule a consultation or call (651) 323-2255.
The content of this article is for informational purposes only and does not constitute legal or tax advice. Consult a qualified tax professional for guidance specific to your situation.
