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You already know the conversation is coming. A client calls, forwards a notice, or asks why the balance they thought was manageable just grew again. Whether you are advising individuals on a lingering tax debt, walking a corporate client through estimated payments, or studying for your EA or CPA Exam credential while working in practice, the IRS interest rate is one of those quiet numbers that changes every quarter and rarely gets the attention it deserves—until a client sees the total.
For the quarter beginning October 1, 2026, that number is back to 7%. Here is what changed, why it changed, and how to explain it calmly and clearly.
Quick answer: For the quarter beginning October 1, 2026, the IRS interest rate is 7% for individual underpayments and overpayments, compounded daily. Corporations pay 7% on underpayments (9% for large corporate underpayments) but earn only 6% on overpayments (4.5% on amounts above $10,000). Rev. Rul. 2026-15, issued under Internal Revenue Code (IRC) §6621, sets these rates from a 4% federal short-term rate (IRS Newsroom; Internal Revenue Bulletin 2026-36).
The individual overpayment and underpayment rate for the quarter beginning October 1, 2026, is 7% per year, compounded daily, unchanged from the third quarter of 2026 (IRS Newsroom, “Interest Rates Remain the Same for the Fourth Quarter of 2026Opens in new window“). The “again” in this quarter’s headline is really about the year as a whole: the individual rate ran at 7% in the first quarter of 2026, dipped to 6% in the second quarter, then climbed back to 7% for the third and fourth quarters.
That swing matters because the IRS does not average a client’s balance over the year. Each quarter carries its own rate, so a balance that has been outstanding since early 2026 has already crossed three different interest environments. The rate itself is set by Revenue Ruling 2026-15, published in Internal Revenue Bulletin 2026-36Opens in new window, which formally announces the rates under IRC §6621 for the fourth calendar quarter of 2026.
IRC §6621 ties every IRS interest rate to the federal short-term rate, which the Treasury Department redetermines each quarter. For the quarter beginning October 1, 2026, the federal short-term rate, based on daily compounding and determined during July 2026, is 4% (Internal Revenue Bulletin 2026-36).
From that base rate, §6621 adds a fixed spread depending on who owes whom:
Because the Treasury Department sets the federal short-term rate using the first month of the prior quarter, practitioners can often see a rate shift coming a few weeks before it takes effect. Rates never apply retroactively—a change announced for Q4 2026 does not reach back and change what a client owed for interest that accrued in an earlier quarter (IRS, “Quarterly Interest RatesOpens in new window“).
Daily compounding means the stated 7% rate is not the true annual cost—the effective rate runs a bit higher once you account for interest accruing on interest every single day. The IRS confirms that “the interest rates we charge and pay on overpayments and underpayments are compounded daily,” meaning interest is assessed on the previous day’s balance plus the interest already added (IRS, “Quarterly Interest Rates”), a mechanic required under IRC §6622.
Running the math on daily compounding over a full year, a nominal 7% rate works out to roughly 7.25% in effective annual terms. A nominal 9% large corporate underpayment rate compounds to roughly 9.42% effective. These effective-rate figures are illustrative calculations based on the published nominal rates, not numbers the IRS publishes directly, but they show why a balance that looks modest in January can grow faster than clients expect by December.
The other detail worth repeating to every client with an outstanding balance: interest keeps accruing on unpaid tax, penalties, and interest until the full amount is paid, even if the client is on an approved installment agreement (IRS, “Quarterly Interest Rates”). A payment plan stops enforced collection. It does not stop the clock on interest.
Corporations pay a higher rate on money they owe the IRS than they earn on money the IRS owes them, and the gap gets wider at higher balances. For Q4 2026, a corporation underpaying its taxes pays 7% (9% if it qualifies as a large corporate underpayment), while a corporation with an overpayment earns only 6%—and just 4.5% on any portion above $10,000 (IRS Newsroom; Internal Revenue Bulletin 2026-36). That is a spread of up to 4.5 percentage points between what a corporation pays on a large deficiency and what it earns on a large refund.
This is also where a common misconception deserves a direct correction: some clients treat a lingering IRS refund, or an intentional overpayment, as a safe place to park cash—essentially a savings account. It is not. Overpayment interest is taxable income, so the 6% or 4.5% a client earns is a pre-tax figure that shrinks further once ordinary income tax applies. Compare that to the 7% (or 9%) a client pays on an underpayment, and the math almost never favors overpaying the IRS on purpose. If a corporate client has excess cash, a §6603 deposit at 4% to stop interest on a disputed liability, or simply accurate estimated payments, will usually serve them better than an intentional overpayment.
Yes, if a client did not pay enough tax throughout the year, the same 7% rate that applies to a balance due also drives the estimated tax underpayment penalty. IRC §6654 (individuals) and §6655 (corporations) both provide that the addition to tax for underpaying estimated taxes uses the underpayment rate established under §6621—so for the fourth quarter of 2026, that penalty calculation runs on the 7% rate as well (Internal Revenue Bulletin 2026-36).
The safe harbor still offers protection. Individuals generally avoid the penalty if their timely payments equal the lesser of 90% of the current year’s tax or 100% of the prior year’s tax, with that threshold rising to 110% of prior-year tax for taxpayers whose prior-year adjusted gross income exceeded $150,000 ($75,000 if married filing separately). Corporations have a parallel safe harbor under §6655 with its own limits on using the prior-year option. Confirm the exact percentages against the current Form 2210Opens in new window and Form 2220Opens in new window instructions before finalizing a client’s estimated payment strategy, since safe-harbor mechanics are exactly the kind of detail worth double-checking every filing season.
For clients with lumpy or seasonal income, the safe harbor is often the cleanest way to avoid a 7% penalty calculation entirely—base payments on a known prior-year number instead of guessing at the current year.
The IRS is replacing FTA with a new, automatic relief program called AEP, and the transition is already underway. The IRS describes AEP as a systemic administrative relief program “designed to simplify the process and reduce burden for those with a timely compliance history” (IRS Newsroom, “IRS Simplifies Penalty Relief, Introduces Automatic Process for Eligible TaxpayersOpens in new window“). Where FTA requires a practitioner or taxpayer to call and ask for relief, AEP applies automatically for eligible returns.
Here is the transition timeline that matters to your clients right now. FTA remains available for certain returns during the transition, but it must still be requested manually. For original returns with due dates of January 1, 2027, or later, FTA will no longer be available at all—AEP takes over completely (IRS Newsroom, “Automatic Exemption from Penalty: What Taxpayers Should KnowOpens in new window“). AEP generally covers failure-to-file, failure-to-pay, and failure-to-deposit penalties for taxpayers with a clean three-year filing and payment history (or twelve consecutive quarters for quarterly filers). It is important to be precise with clients about what AEP does not do—it does not eliminate the underlying tax liability, it does not stop interest from accruing, and it does not apply to every penalty or every taxpayer.
As J.T. Eagan, DTech, EA, Clinical Assistant Professor at Purdue University and a Gleim Instruct tax professor, puts it: “Every time the IRS retires one relief process and rolls out another, practitioners worry they’ll miss something for a client. You won’t, if you treat it like any other regulatory update—read the transition rules once, calmly, and build them into your year-end checklist.”
Start by separating the rate from the penalty, because clients often conflate the two. Interest at 7%, compounded daily under IRC §6621, applies to any unpaid balance regardless of fault. Penalties are a separate charge for late filing, late payment, or underpaying estimates, and those are the ones AEP or FTA can potentially remove—interest keeps running either way.
From there, a short year-end conversation should cover three things—the current 7% rate and how daily compounding adds to a stalled balance, whether the client’s estimated payments meet the §6654 or §6655 safe harbor, and whether the client’s compliance history would qualify for AEP relief if a penalty does hit. For clients still confused about overpayment interest, remind them plainly that any interest the IRS pays them is taxable and rarely beats the cost of an underpayment—it is compensation for money borrowed, not a return on savings.
The individual rate returns to 7% because the federal short-term rate that drives IRC §6621 came in at 4% for the month used to set the quarter, plus the statutory 3-percentage-point add-on. The rate had dropped to 6% for the second quarter of 2026 before climbing back to 7% for the third and fourth quarters, so “again” reflects a return to the higher rate rather than a brand-new increase (Internal Revenue Bulletin 2026-36).
Under IRC §6622, the IRS compounds interest daily, meaning each day’s interest is calculated on the prior day’s balance plus any interest already added. This makes the true annual cost slightly higher than the stated rate—a nominal 7% rate works out to roughly 7.25% effective over a full year—and it keeps accruing on unpaid tax, penalties, and interest until the balance is paid in full.
For the quarter beginning October 1, 2026, corporations pay 7% on standard underpayments and 9% on large corporate underpayments, while earning only 6% on standard overpayments and just 4.5% on the portion of an overpayment exceeding $10,000. That spread means overpaying the IRS is rarely an efficient way for a corporation to hold cash.
FTA required a taxpayer or practitioner to actively request relief from the IRS, one time, for a first penalty. AEP applies automatically to eligible taxpayers with a clean multi-year compliance history, without a request. FTA remains available during the transition but must still be requested manually; for returns due on or after January 1, 2027, only AEP will apply.
Yes—the interest rate and penalty relief are separate issues. A higher IRS interest rate does not affect whether a client qualifies for AEP or, during the transition period, FTA. Penalty relief depends on the client’s filing and payment compliance history, not on the current §6621 rate; interest continues to accrue on any unpaid balance regardless of penalty relief.
Quarterly interest resets, safe-harbor math, and penalty-relief transitions like the shift from FTA to AEP are the kind of detail that separates a preparer who reacts to IRS notices from one who anticipates them for clients. Building that fluency and being able to explain it in plain terms, the way we do here is a large part of what makes the Enrolled Agent (EA) credential valuable for anyone advising clients on federal tax matters.
We are committed to helping accounting professionals build that kind of confidence, with real Gleim Instruct professors like J.T. Eagan, DTech, EA, guiding you through the tax law changes that show up in client conversations long before they show up on an exam. If you are preparing for the EA exam, working toward the Annual Filing Season Program (AFSP) as a tax preparer, or weighing the EA credential alongside a CPA or broader tax track, take a look at the Gleim EA Review course, built with SmartAdapt™ technology and backed by the Access Until You Pass® guarantee.