Large Corporation Estimated Tax: Installments, Penalties, and CAMT

A corporation is subject to the large corporation estimated tax rules if it reported taxable income of $1 million or more in any of the three tax years before the current one. The consequence is stricter than for other businesses: quarterly installments generally must be built on an accurate projection of the current year’s tax, not the prior year’s return, and underpayments accrue a daily-compounding penalty tied to the federal short-term rate. That rate ran 7% in the first quarter of 2026 and 6% in the second.¹

Who Counts as a Large Corporation

The test is a three-year look-back. A corporation (or any predecessor) that had $1 million or more in taxable income in any single year of that window is classified as large for the current year.² For a 2026 tax year, that means checking 2023, 2024, and 2025. Hitting the line in one of those years is enough.

The taxable income figure used for the test does not include net operating loss carrybacks or capital loss carrybacks, so a corporation cannot pull historical income below $1 million using later carrybacks.² The classification looks at net taxable income only, not gross revenue or assets.

Controlled Groups Share the Threshold

Members of a controlled group do not each get a full $1 million. The threshold is divided among component members under rules similar to those used to allocate corporate tax bracket amounts under Section 1561.² Equal shares are the default, but all members can consent to an alternative allocation.³

A subsidiary that earns $400,000 might look safely under the line on its own. In a five-member group with an equal split, its share of the threshold is $200,000, and it is a large corporation. Losses at one member cannot offset another member’s income for this test.³

No Prior-Year Safe Harbor, With One Narrow Exception

Most corporations can base their required annual payment on the lesser of 100% of the current year’s tax or the tax shown on the prior year’s return. That prior-year safe harbor is what makes quarterly planning predictable for smaller companies.

Large corporations lose it, with one exception. The statute allows a large corporation to base its first quarterly installment on 25% of the prior year’s tax.² Whatever shortfall that produces compared with a current-year projection must be made up in the second installment. Total payments through the second installment must reach 50% of the current-year projected tax; through the third, 75%; through the fourth, 100%.

The practical result is that a large corporation needs a working current-year tax projection at every quarterly deadline. Waiting until year-end is not an option, and an underestimate at any point starts a penalty clock running from that installment date.

The Annualized Income Installment Method

Because installments must track the current year, most large corporations use the annualized income installment method. It sizes each payment to the income actually earned through a defined window, then scales that income to a full-year figure and computes the tax on it.

The standard measurement windows are the first 3 months for the first installment, the first 3 months again for the second, the first 6 months for the third, and the first 9 months for the fourth. Two elective alternatives exist: 2, 4, 7, and 10 months, or 3, 5, 8, and 11 months.⁴ The alternative periods can fit better when revenue and expenses concentrate at particular points in the fiscal year.

For each installment, the annualized tax is multiplied by a cumulative percentage — 25%, 50%, 75%, 100% — and prior payments are subtracted from that cumulative target.² Heavy early-year profits scale up under annualization and push installments higher; slower months pull them down. Calculations are reported on Schedule A of Form 2220.⁵

The Seasonal Alternative

Corporations with a consistent seasonal pattern can instead use the adjusted seasonal installment method. It is available when at least 70% of taxable income for the year falls within any six consecutive months, based on a comparison to prior years.⁶ It fits businesses like agriculture, tourism, and retail that earn most revenue in predictable windows.

When Installments Are Due

For a calendar-year corporation, the four installments are due April 15, June 15, September 15, and December 15. Fiscal-year corporations pay on the 15th day of the 4th, 6th, 9th, and 12th months of their tax year. If the 15th is a Saturday, Sunday, or legal holiday in the District of Columbia, the deadline moves to the next business day.⁷

Electronic Payment Is Almost Always Required

A corporation that deposits more than $200,000 in total federal depository taxes during a calendar year must use the Electronic Federal Tax Payment System for all federal tax deposits after that, including corporate estimated tax.⁸ That threshold counts employment and withheld income taxes too, so corporations with meaningful payroll typically cross it. Depositing outside EFTPS when required carries a separate 10% penalty on the amount that should have been sent electronically.⁹ The right amount paid the wrong way still triggers a charge.

What an Underpayment Costs

When any quarterly deposit falls short, Section 6655 imposes an addition to tax equal to interest on the shortfall at the federal short-term rate plus three percentage points, compounded daily.² The rate resets each quarter. For 2026, it was 7% in the first quarter and 6% in the second.¹

Each installment is evaluated on its own. A shortfall on the first due date starts accruing from that date and keeps accruing until it is covered or until the return is due, whichever comes first. Catching up in a later quarter stops future accrual but does not erase what has already built up, so early-year underpayments are the most expensive.

Form 2220 is where the calculation, and any annualization or seasonal method, gets documented. A large corporation that used the prior-year 25% option for its first installment must attach Form 2220 to its return even when no penalty is owed.⁵ Skipping it can produce an erroneous penalty notice.

Relief is narrow. There is no penalty if the tax shown on the return is under $500.² Otherwise there is no standing exception for downturns, cash-flow strain, or volatile income. Annualization is the tool for handling fluctuation without penalty.

Corporate Alternative Minimum Tax

The corporate alternative minimum tax applies to corporations with average annual adjusted financial statement income above $1 billion. CAMT liability is part of a corporation’s total tax and must be built into estimated payments.

The IRS waived estimated tax penalties attributable to CAMT for 2023 and extended similar relief for 2024 and 2025.¹⁰ Affected corporations still had to file Form 2220 and could exclude the CAMT portion when computing the required annual payment. As of early 2026, no formal extension has been announced for the 2026 tax year. Plan installments assuming the penalty applies unless further relief is issued.

Recovering an Overpayment Before You File

Overshooting is common when income projections come in high and then soften. Form 4466 lets a corporation apply for a quick refund of overpaid estimated tax, but only if the overpayment is at least 10% of expected tax liability and at least $500.¹¹

The window is tight. Form 4466 must be filed after the tax year ends but before the income tax return is filed, and no later than the unextended due date for that return. A filing extension does not extend the Form 4466 deadline.¹¹ For a calendar-year corporation, that means the form has to reach the IRS by April 15. Filing the return first closes the quick refund door, and the overpayment must then be claimed as a credit or refund on the return itself.

1
Internal Revenue Service. Quarterly Interest Rates
2
Office of the Law Revision Counsel. 26 USC 6655 – Failure by Corporation to Pay Estimated Income Tax
3
govinfo.gov. 26 CFR 1.6655-4 Large Corporations
4
eCFR. 26 CFR 1.6655-2 – Annualized Income Installment Method
5
Internal Revenue Service. Instructions for Form 2220 (2025) – Underpayment of Estimated Tax by Corporations
6
eCFR. 26 CFR 1.6655-3 – Adjusted Seasonal Installment Method
7
Internal Revenue Service. Publication 509 (2026), Tax Calendars
8
eCFR. 26 CFR 31.6302-1 – Deposit Rules for Taxes Under the Federal Insurance Contributions Act (FICA) and Withheld Income Taxes
9
Internal Revenue Service. Information About Your Notice, Penalty and Interest
10
Internal Revenue Service. Relief From Additions to Tax for Underpayments Applicable to the New Corporate Alternative Minimum Tax
11
Internal Revenue Service. Instructions for Form 4466