IRS interest: how it builds and the few ways to stop it

The IRS announced in news release IR-2026-98 that its interest rates would stay where they were for the calendar quarter that began October 1, 2026: 7% a year on underpayments, and 9% on large corporate underpayments. The rate is the part you can look up. How IRS interest attaches to a balance, and the short list of things that stop it, is the part that decides what a dispute costs.

This is a federal piece. Oklahoma has its own interest rules for state taxes, and nothing here describes them. But the owners of closely held Oklahoma and Texas companies file federal returns for the business and for themselves, and when an examination reaches back several years, the federal interest line is often the number nobody planned for.

Where IRS interest starts: the original due date

The general rule sits in section 6601 of the Internal Revenue Code, and it's short. If tax isn't paid by the last date prescribed for payment, interest runs from that date until the date it's paid.

That last date is fixed early. The statute says it's determined without regard to any extension of time for payment or any installment agreement, and the IRS's interest page adds that extensions to file don't extend the date for payment.

Here's how that surfaces in practice. An examination opens two or three years after a return was filed and ends, some time later, with additional tax. Interest on that tax didn't begin when the audit began; it began on the original due date, before anyone knew there was a disagreement.

What the interest runs on

The tax itself

Interest runs first on the unpaid tax, and section 6601 provides that it's assessed and collected in the same manner as the tax.

The penalties, on two different clocks

Penalties draw interest too, and the starting point depends on which penalty it is.

For the failure-to-file and accuracy-related penalties, interest runs from the date the return was required to be filed, including any extensions, until the penalty is paid.

Most other penalties work differently. Interest applies only if the penalty isn't paid within 21 calendar days of the notice and demand for it, meaning the IRS's formal bill (10 business days if the amount demanded is $100,000 or more), and then only from the date of that notice. The IRS's interest page lists the failure-to-pay and estimated tax penalties among those whose interest starts with a notice or assessment.

So a large accuracy-related penalty proposed at the end of a long audit arrives with years of interest already attached.

How it compounds, and why the rate keeps moving

Section 6622 is brief: interest under the Code is compounded daily. Each day's interest joins the balance, and the next day's is figured on the larger number.

The rate comes from section 6621. For underpayments it's the federal short-term rate, a benchmark the Treasury determines, plus 3 percentage points, and that benchmark is redetermined for each calendar quarter. The IRS notes that a change doesn't affect the interest charged for prior quarters, so a balance that spans several years is computed in layers, each at the rate in force at the time.

C corporations face a higher tier. When a C corporation's underpayment for a taxable period exceeds $100,000, the statute substitutes 5 percentage points for the usual 3, for periods after an applicable date the statute defines.

The notice window

Two timing rules sit at the point where a balance becomes a bill.

First, the grace period. If the amount in a notice and demand is paid within 21 calendar days after the notice date (10 business days when the amount is $100,000 or more), no interest is charged on the amount paid for the period after the notice date. The IRS's interest page has a related statement, framed around the notice's pay-by date: a taxpayer who pays the amount shown in full on or before that date isn't charged interest on it.

Second, the waiver rule. It applies to a deficiency, which in rough terms is additional income, estate, gift or certain excise tax the IRS determines beyond what was reported. The statute refers to a waiver of the restrictions on assessing that deficiency. In our shorthand, that's the taxpayer agreeing in writing that the IRS may go ahead and assess it.

If the IRS then doesn't make notice and demand within 30 days after the waiver is filed, section 6601 stops interest on the deficiency from immediately after that 30th day until the date of the notice and demand. In our experience it's one of the first things to check when an agreed case sat for months before the bill arrived.

Why reasonable cause doesn't reach interest

Penalties get most of the attention in a controversy, and for an understandable reason: many of them can be removed when the taxpayer shows reasonable cause. We cover that ground in our overview of penalty abatement.

Interest is different. The IRS says so in one sentence on its interest page: "We don't remove or reduce interest for reasonable cause or as first-time relief."

Good faith doesn't move the interest line, and neither does a clean compliance history. Think of a taxi meter in stopped traffic. It keeps turning no matter who caused the jam.

There's one indirect exception. When tax or a penalty is reduced, through an amended return or penalty relief, the IRS says it automatically reduces the related interest. In our experience that's often the only interest relief a taxpayer ever sees: the interest that had built up on a penalty goes away because the penalty did.

In a dispute that runs for years, that leaves the decisions controlling interest to be made early, usually before anyone has focused on it.

The short list of tools that stop or reduce it

Pay, or make a deposit, while the dispute runs

Paying the tax stops interest on the amount paid. The less familiar tool is the deposit under section 6603.

A taxpayer may make a cash deposit that the IRS can use to pay income, estate, gift or certain excise tax that hasn't been assessed yet. To the extent the deposit is later used to pay the tax, the tax is treated as paid when the deposit was made, so underpayment interest doesn't run on that amount in the meantime.

What separates a deposit from a payment is the way back. The statute directs the IRS to return any unused part of a deposit on the taxpayer's written request, unless it determines that collection of the tax is in jeopardy. A payment, as we frame the contrast, is applied to the liability, and getting it back generally means pursuing a refund claim.

Deposits have a cost. A returned deposit earns interest only to the extent it's attributable to a "disputable tax," meaning the taxpayer's reasonable estimate, specified at the time of the deposit, of the maximum tax attributable to disputable items.

Even then the rate is the federal short-term rate alone, 3 points below the underpayment rate. A taxpayer who deposits and then wins has parked cash at a low return.

One anchor helps with that estimate. Once a 30-day letter has been issued (the first letter of proposed deficiency that offers review in the IRS Independent Office of Appeals), the disputable tax can't be less than the deficiency proposed in that letter. We describe that stage in what happens in IRS Appeals after the audit.

Here's a pattern we see often. The deposit question gets raised late, after a case has sat in Appeals for a year or more, when the interest it could have stopped has already compounded. It belongs in the first conversation about contesting a proposed adjustment.

Abatement for IRS error or delay

Section 6404(e)(1) allows the IRS to abate interest attributable to an unreasonable error or delay by an IRS officer or employee in performing a ministerial or managerial act. Three limits are built into the text.

• The word is "may." Relief is discretionary.
• An error or delay counts only if no significant aspect of it can be attributed to the taxpayer.
• It counts only after the IRS has contacted the taxpayer in writing about the deficiency or payment, so quiet years before that first letter are outside the rule.

The regulations define the two key terms narrowly. A ministerial act is a procedural or mechanical act that involves no judgment or discretion and that occurs after all prerequisites, such as conferences and supervisory review, have taken place. A managerial act is an administrative act during the processing of a case that involves the loss of records or the exercise of judgment or discretion about managing personnel.

Examples in the regulation show where the line falls. A clerical employee misplacing the case file is a managerial act, and so is leaving a case unassigned while the agent is on extended sick leave. Issuing a notice of deficiency (the formal determination letter that precedes a Tax Court case) once it has been prepared and reviewed is a ministerial act, so an unreasonable delay at that step can qualify.

On the other side, holding a case until a related tax shelter examination is finished is a general administrative decision, and waiting on Chief Counsel advice about a substantive legal question reflects a decision about the proper application of federal tax law. Neither supports abatement. Where the taxpayer's own conduct caused part of the delay, as in the regulation's example of a taxpayer who moves twice mid-audit, only the IRS-caused slice can be abated.

This is why we say an abatement claim is built from a calendar: a dated timeline that starts with the first written contact and accounts for every gap. Much of what frustrates taxpayers about a slow case, in our experience, turns out to be workload prioritization or legal analysis, and neither qualifies. Time a case spends in Appeals or in court because the taxpayer chose to contest it is hard to describe as IRS delay at all.

A request goes on Form 843 or in a signed letter, with a detailed description and supporting documents. The Form 843 instructions point to box a on line 7 and ask for a line 8 explanation that covers the type of tax, when the IRS first gave written notice about the deficiency or payment, the specific period for which abatement is requested, and why failing to abate would be grossly unfair.

Two boundaries matter if you run a business. This relief is available only for taxes that require a notice of deficiency, which the instructions list as income, generation-skipping transfer, estate and gift, and certain excise taxes. Interest on employment taxes can't be abated this way, so a company whose federal problem is payroll tax won't find help here.

There's also a clock. The IRS's interest abatement page lists a filing window of 3 years from when the return was originally filed or 2 years from the payment of the tax, whichever is later.

The 36-month suspension for individuals

Section 6404(g) doesn't depend on proving anyone's mistake. It covers an individual who filed an income tax return on time, counting extensions.

If the IRS doesn't provide a notice specifically stating the liability and the basis for it within 36 months, interest and certain time-based penalties are suspended. Those 36 months run from the later of the date the return was filed or its due date without regard to extensions. The suspension starts the day after that period closes and ends 21 days after the notice is provided.

The exceptions are broad enough to check every time. Excluded are tax shown on the return, penalties under section 6651 (the failure-to-file and failure-to-pay section), cases involving fraud, gross misstatements, certain reportable transactions and listed transactions, and criminal penalties.

As we read it, because the rule is written for individuals, it can reach an owner's personal income tax return but not a C corporation's own balance.

Erroneous refunds

The last item is mandatory. When the IRS issues a refund by mistake and later asks for it back, section 6404(e)(2) says the IRS "shall" abate the interest on that erroneous refund until the date it demands repayment. Two exceptions apply: the taxpayer or a related party caused the erroneous refund in some way, or the refund exceeds $50,000.

Where a denial can be reviewed

What happens when the IRS says no? Its interest abatement page says a taxpayer who disagrees with the determination can appeal the decision.

Section 6404(h) then gives the Tax Court jurisdiction to decide whether the failure to abate interest was an abuse of discretion, and to order an abatement if it was. In our view, that asks for more than simple disagreement with the result.

Timing is specific. An action can be brought once the IRS mails its final determination not to abate, or once 180 days have passed since the claim was filed, and no later than 180 days after the final determination is mailed.

It's also limited to taxpayers who meet the requirements referred to in section 7430(c)(4)(A)(ii), which include a net worth requirement. Our article on whether to take a case to Tax Court covers the broader choice of forum.

Interest in the other direction

The same machinery can work for a taxpayer. The IRS pays interest on overpayments, although section 6621 sets the corporate overpayment rate at the federal short-term rate plus 2 points (plus 0.5 for the part of an overpayment above $10,000), below what a corporation is charged on an underpayment. The IRS also notes that it typically has 45 days of administrative time to issue a refund without paying interest on it.

If a federal examination or appeal is running long and the interest line has started to matter, that's a good moment for a conversation. You can reach us through the contact page or at our Oklahoma City office. Raising the timeline and the deposit question early usually leaves more options open than raising them at the end.

This article is general information about Oklahoma, Texas, and federal law, not legal advice, and it does not create an attorney-client relationship. Facts matter; talk to a lawyer about yours.