The December 15 tax deadline is the one date in December that catches people off guard: calendar-year C corporations must make their fourth and final estimated tax installment for 2026 on Tuesday, December 15, 2026. Unlike individuals, whose fourth installment falls in January, corporations pay their last installment inside the same tax year. Miss it or underpay it, and the underpayment interest starts running from December 15 — not from the April filing deadline.
The date surprises people because it breaks the pattern they know from personal taxes. Individuals pay quarterly estimates in April, June, September, and January. Corporations pay on the 15th day of the 4th, 6th, 9th, and 12th months of their tax year — for a calendar-year corporation, that is April 15, June 15, September 15, and December 15, 2026. None of the four 2026 dates falls on a weekend or federal holiday, so none of them shifts. For the full quarterly calendar, see our quarterly tax due dates for 2026.
What the December 15 Tax Deadline Covers
The deadline covers the fourth installment of estimated tax for calendar-year C corporations. A corporation must make estimated payments if it expects to owe $500 or more in federal income tax for the year, after credits. Each installment is generally 25 percent of the required annual payment, which is normally the lesser of 100 percent of this year's tax or 100 percent of last year's tax. Large corporations — those with taxable income of $1,000,000 or more in any of the three preceding years — lose the prior-year safe harbor and must pay on the current year's figure.
Before you pay, project the full year's profit. A strong fourth quarter can push the company into a larger bill than the first three installments assumed, and a shortfall on the December payment draws underpayment interest even if the earlier payments were on time. The IRS figures the penalty on Form 2220, installment by installment, so a December shortfall is charged from December 15. For the fourth quarter of 2026, the underpayment rate is 7 percent for corporations and 9 percent for large corporate underpayments, per IR-2026-98.
December 15 Tax Deadline: How Corporations Pay
Corporations pay electronically through EFTPS, the free payment service of the U.S. Treasury — there is no form to file with the payment. The old worksheet, Form 1120-W, was retired after tax year 2022; the IRS now points corporations to the estimated tax worksheet in Publication 542. Enroll in EFTPS ahead of time if you have not used it: enrollment takes days, and the deadline does not wait for it.
Payments over $1 million must be scheduled by 8 p.m. ET at least one calendar day before the due date — for this installment, by 8 p.m. ET on Monday, December 14. Smaller payments can be scheduled closer to the date, but do not leave it to the last hour: a payment that posts late is a late payment. Keep the EFTPS confirmation number with the company's tax file; it is the proof the payment was made on time. The books that support the estimate should already be reconciled — our bank statement to Excel converter turns the year's statements into the spreadsheet the estimate is built on.
Who Does Not Pay on December 15
Most individuals do not pay on December 15, and this is where the confusion costs money. Pass-through owners — partnerships, S corporations, and sole proprietorships — pay estimated tax through their individual quarterly estimates, and their fourth installment is due January 15, 2027, not December 15. The same goes for freelancers and gig workers: the January date is theirs. If you pay on December 15 by mistake, the money is not lost, but the timing of the credit changes, and the January payment still has to be made.
Fiscal-year corporations follow their own schedule: the 15th day of the 4th, 6th, 9th, and 12th months of their own tax year. A corporation with a June 30 fiscal year-end, for example, owes installments on October 15, December 15, March 15, and June 15. And states have their own estimate deadlines — many follow the federal pattern, but some do not, so check the state calendar too. For the year-end moves that sit beside this deadline, see our guide to year end tax planning for 2026.
What Happens If You Miss the December 15 Tax Deadline
Missing the December 15 tax deadline triggers underpayment interest on the shortfall, running from the installment date. The charge is interest, not a flat penalty, and it is figured on Form 2220 for each installment separately. A corporation that pays late but in full by April still owes the interest for the months between December and April. The practical fix is to pay what you can now and true it up at filing — a partial payment reduces the interest, and an amended estimate is better than a silent miss.
The best defense is a clean set of books going into December. Reconcile every account to its statement, confirm the year's income and expenses, and run the estimate from real numbers rather than a guess. A company that knows its profit to the dollar can pay the right installment on the right day; a company guessing from memory usually pays the wrong amount on the wrong day. Keep the statements, the EFTPS confirmation, and the Form 2220 workpapers together — if the IRS asks, the file should answer the question by itself.
