IRS Form 1120-W: Corporate Estimated Tax Due Dates and Penalties

IRS Form 1120-W is the worksheet a C corporation uses to figure out how much to pay in quarterly estimated federal income tax. You don’t file it with the IRS. It stays in your records as the calculation behind four installment payments you send during the year, and it applies whenever your corporation expects to owe $500 or more in income tax after credits.¹

Which Corporations Have to Pay Estimated Tax

The $500 threshold is the trigger. If your net tax after credits will hit that figure for the year, quarterly payments are required.¹ This covers C corporations and LLCs that have elected C corporation tax treatment. Because the test uses net tax rather than gross tax, credits can drop you below the threshold and out of the requirement.

Two boundaries are worth knowing. Tax-exempt organizations only owe estimated payments on unrelated business income tax, and only once that liability itself reaches $500.² A corporation with a short tax year of fewer than four full calendar months is exempt from estimated tax for that period.³

How the Worksheet Calculates Your Payment

Start with your projected taxable income for the full year. Apply the flat 21% corporate rate. Subtract the credits you reasonably expect to claim, such as the general business credit or the foreign tax credit. What’s left is your estimated tax for the year.

That total gets split into four equal installments of 25% each.¹ The number you’re actually required to cover, called the required annual payment, is the lesser of 100% of the current year’s tax or 100% of last year’s tax, provided last year was a full 12-month period showing a tax liability.⁴ Many corporations base payments on last year’s actual tax because the figure is fixed and known.

If your projections change mid-year, redo the worksheet and adjust the remaining installments. There’s no penalty for recalculating, and letting a shortfall accumulate until the annual return is due can be expensive.

When the Payments Are Due

Calendar-year corporations pay on four dates:⁵

1st installment: April 15
2nd installment: June 15
3rd installment: September 15
4th installment: December 15

These are the 15th days of the 4th, 6th, 9th, and 12th months of the tax year. Fiscal-year corporations follow the same pattern counted from the start of their own tax year. When a date lands on a weekend or federal holiday, the deadline moves to the next business day.⁵ The gap between the first and second payments is only two months, and that’s where corporations most often miss.

How to Send the Money

Corporate estimated tax payments have to be made electronically. The standard route is the Electronic Federal Tax Payment System (EFTPS), a free Treasury service that lets you schedule payments in advance.⁶ Enrollment takes time because credentials arrive by mail, so a new corporation should sign up well before its first due date.⁷ Alternatives include arranging ACH credit or same-day wire through a bank, or letting a tax professional deposit on your behalf.

Uneven Income: The Annualized Installment Method

Equal quarterly payments assume income arrives at a steady pace. Retailers, construction companies, and early-stage businesses know it doesn’t. Paying 25% of an annual estimate in April on income you haven’t earned yet ties up cash you may need.

The annualized income installment method lets you size each installment to the income you actually earned through a set annualization period. Under the default schedule, the first two installments look at the first 3 months of income, the third at 6 months, and the fourth at 9 months. Each period’s income is annualized to a full-year figure, and cumulative targets of 25%, 50%, 75%, and 100% set how much you should have paid by each deadline. Corporations with unusual patterns can elect alternative periods by filing Form 8842.⁸ The math gets involved fast, and most corporations that use this method run it through tax software or a preparer.

Avoiding the Underpayment Penalty

When installments fall short, the IRS charges a penalty computed on Form 2220. It behaves like interest on the shortfall, running from the missed due date until the payment is made or the return is due.¹ To stay clear, your total estimated payments have to cover the smaller of two safe-harbor amounts:

100% of the current year’s tax as shown on the return you eventually file
100% of the prior year’s tax, if that return covered a full 12 months and showed a tax liability

The prior-year figure is popular because it’s already known. It has one big limit.

The Large Corporation Rule

A large corporation is one that had taxable income of $1 million or more in any of the three preceding tax years, measured without net operating loss or capital loss carrybacks. A single strong year in that lookback window can flag your corporation as large even if the other two years were losses.¹

Large corporations can’t use the prior-year safe harbor for the second, third, and fourth installments. Those must be based on 100% of the current year’s tax.¹ The first installment can still lean on last year’s tax, but any reduction from doing so has to be added back to the second installment.

Interest Rates on Shortfalls

The penalty rate is the federal short-term rate plus 3 percentage points for most corporations, and the short-term rate plus 5 points for large corporate underpayments, compounded daily from each installment due date.⁹ Rates reset quarterly. For Q1 2026, the general corporate underpayment rate is 7% and the large corporate rate is 9%.¹⁰ For Q2 2026, those drop to 6% and 8%.¹¹

A Note on the Corporate Alternative Minimum Tax

The Corporate Alternative Minimum Tax (CAMT), introduced by the Inflation Reduction Act, is a 15% minimum tax on adjusted financial statement income for applicable corporations. Applicable corporations are generally those with average annual adjusted financial statement income above $1 billion over three years; foreign-parented groups face a $1 billion global test plus a $100 million U.S. test. S corporations, regulated investment companies, and REITs are excluded. If CAMT applies, the excess over regular tax plus credits would ordinarily flow into estimated tax. The IRS has announced penalty relief waiving the estimated tax penalty for CAMT-attributable underpayments during implementation.¹² That relief is temporary, and corporations near the threshold should watch for updated guidance.

Getting a Refund If You Overpaid

If your corporation pays more estimated tax than it ends up owing, you don’t have to wait for the annual return to recover the money. Form 4466 is an application for a quick refund of overpaid estimated tax, and the IRS must act on it within 45 days.¹³ The overpayment has to meet two thresholds:

At least 10% of the corporation’s expected tax liability for the year
At least $500

Timing is strict. File Form 4466 after the end of the tax year but before the original due date of the income tax return, and before you actually file the return. For a calendar-year corporation, that window runs from January 1 through April 15. Extending your income tax return does not extend the Form 4466 deadline.¹³ Applications with material errors or omissions the IRS can’t resolve in 45 days may be denied.

1
Office of the Law Revision Counsel. 26 USC 6655 – Failure by Corporation to Pay Estimated Income Tax
2
Internal Revenue Service. Instructions for Form 2220
3
eCFR. 26 CFR 1.6655-5 – Short Taxable Year
4
Internal Revenue Service. Instructions for Form 2220
5
Internal Revenue Service. Underpayment of Estimated Tax by Corporations Penalty
6
Internal Revenue Service. EFTPS The Electronic Federal Tax Payment System
7
Electronic Federal Tax Payment System. Electronic Federal Tax Payment System
8
eCFR. 26 CFR 1.6655-2 – Annualized Income Installment Method
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Internal Revenue Service. Topic No. 653, IRS Notices and Bills, Penalties and Interest Charges
10
Internal Revenue Service. Interest Rates Remain the Same for the First Quarter of 2026
11
Internal Revenue Service. Internal Revenue Bulletin 2026-8
12
Internal Revenue Service. Relief From Additions to Tax for Underpayments Applicable to the New Corporate Alternative Minimum Tax
13
Internal Revenue Service. Instructions for Form 4466 – Corporation Application for Quick Refund of Overpayment of Estimated Tax