Corporation Tax Interest: Rates, Overpayments, and Abatement

Corporation tax interest rates run on a simple formula: the IRS charges the federal short-term rate plus three percentage points on unpaid corporate taxes, compounded daily, and pays the short-term rate plus two points on overpayments. For the second quarter of 2026, that works out to 6% on underpayments and 5% on overpayments. Two adjustments shift those numbers in specific situations: a higher 8% rate applies to large corporate underpayments once an IRS deficiency notice has aged 30 days, and the overpayment rate drops sharply on the portion of a refund exceeding $10,000.¹²

The Standard Underpayment Rate

Interest starts accruing the day after a corporate tax payment is due and does not stop until the balance is paid. The rate is reset at the beginning of each calendar quarter and equals the federal short-term rate plus three points.¹ For April through June 2026, that rate is 6% annually for both corporate and non-corporate underpayments.²

Compounding is daily. The IRS divides the annual rate by 365 (366 in a leap year) and applies that fraction each day, so yesterday’s interest earns interest today.³ On a $500,000 balance at 6%, that produces roughly $82 of interest per day, and the base grows every 24 hours.

One boundary worth flagging: daily compounding does not apply to the estimated tax penalty. That charge uses the same underlying interest rate but is computed as a penalty under the estimated tax provisions, without the daily compounding mechanic.³

The Higher Rate on Large Corporate Underpayments

C corporations with underpayments above $100,000 face the federal short-term rate plus five points instead of three.⁴ For Q2 2026 that is 8%.² S corporations, regulated investment companies, and real estate investment trusts are not subject to this higher rate.⁵

The higher rate is not immediate. It begins on the 30th day after the earlier of two events: the IRS sending a first letter of proposed deficiency that allows an administrative review, or the sending of a statutory notice of deficiency.¹ The standard rate governs until that 30-day window closes. Once the higher rate turns on, it applies to the full underpayment above the $100,000 threshold and compounds daily. Responding to IRS notices quickly is one of the few ways to keep the rate from stepping up.

What the IRS Pays on Overpayments

When a corporation overpays, the IRS pays interest back at the federal short-term rate plus two points, compared with the three points individuals receive.⁶ For Q2 2026 that is 5% for corporations and 6% for individuals.²

The rate drops on the portion of a corporate overpayment above $10,000. Any excess earns only the federal short-term rate plus half a point, which is 3.5% for Q2 2026.⁶ A corporation carrying a $200,000 overpayment earns 5% on the first $10,000 and 3.5% on the remaining $190,000. Parking corporate cash with the IRS is a weak return by design.

The 45-Day Processing Window

The IRS owes no interest on a refund it processes within 45 days of the later of the return’s due date or its actual filing date.⁷ Past 45 days, interest accrues back to the date of the overpayment. Filing early starts that clock sooner.

Overpayment Interest Is Taxable

Any interest the IRS pays on a refund is taxable income in the year received. It gets reported on the corporation’s return the same way bank interest would.

Avoiding Underpayment Interest Through Estimated Payments

Corporations pay estimated tax in four installments, each 25% of the required annual payment. The required annual payment is the lesser of 100% of the current year’s tax or 100% of the prior year’s tax, provided the prior year covered 12 months and showed some tax liability.⁸ Hitting either figure avoids the estimated tax penalty.

Large corporations get less leeway. Any corporation with $1 million or more of taxable income in one of the three preceding tax years can use the prior-year safe harbor only for its first installment. The remaining three quarters must be based on 100% of the current year’s actual tax, with any first-quarter shortfall from using the prior-year figure rolled into the second installment.⁹⁸

Corporations use Form 2220 to determine whether an estimated tax penalty is owed and, if so, the amount.¹⁰

Penalties Running Alongside Interest

Interest and penalties are separate charges that both apply to an unpaid balance. The failure-to-pay penalty is 0.5% of the unpaid tax per month or partial month, capped at 25%. It rises to 1% per month once the tax is still unpaid 10 days after an IRS notice of intent to levy. It falls to 0.25% per month for corporations that filed on time and are in an installment agreement.¹¹

When the IRS applies a payment, it hits tax first, then penalties, then interest. Because interest keeps accruing on any remaining tax, a partial payment often leaves the interest line barely moved: the payment was absorbed by the underlying tax and penalty before reaching it.

When Interest Can Be Reduced

The IRS can abate interest when the accrual resulted from an unreasonable error or delay by an IRS employee performing a ministerial or managerial act. A ministerial act is a routine procedural step involving no judgment, like processing a return once every prerequisite is in place. A managerial act covers administrative decisions such as losing records or reassigning personnel.¹²

Abatement is narrow. It reaches only the interest that accrued during the specific period of the IRS error or delay, not all interest on the account. The taxpayer cannot have contributed to the delay, and the underlying tax must be income, estate, gift, or certain excise tax; employment taxes are excluded.¹² The request goes on Form 843 and needs to identify the tax type, the date the IRS first made written contact, the period at issue, and the reasons declining to abate would be grossly unfair.¹³

Penalties are easier to remove than interest. The IRS applies a First Time Abate policy to penalties and will also waive them for reasonable cause. Interest itself is rarely abated outside the narrow IRS-error path.¹¹

1
Office of the Law Revision Counsel. 26 USC 6621 Determination of Rate of Interest
2
Internal Revenue Service. Quarterly Interest Rates
3
Office of the Law Revision Counsel. 26 USC 6622 Interest Compounded Daily
4
eCFR. 26 CFR 301.6621-3 – Higher Interest Rate Payable on Large Corporate Underpayments
5
Internal Revenue Service. Internal Revenue Manual – 20.2.5 Interest on Underpayments
6
Office of the Law Revision Counsel. 26 USC 6621 – Determination of Rate of Interest
7
Internal Revenue Service. Interest
8
Office of the Law Revision Counsel. 26 USC 6655 – Failure by Corporation to Pay Estimated Income Tax
9
Internal Revenue Service. Instructions for Form 2220
10
Internal Revenue Service. About Form 2220, Underpayment of Estimated Tax by Corporations
11
Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
12
Internal Revenue Service. Interest Abatement
13
Internal Revenue Service. Instructions for Form 843