Tax Year and Due Dates

Electing a tax year

• The first return makes the election. The first tax year begins on the date of incorporation and ends on the chosen year-end, so the first year is almost always short. No Form 1128 is needed to adopt the first year.
• A tax year is 12 months, ends on the last day of a month (unless a 52–53 week year is elected), and must be the same period used for the books (§441(c), (e)). A corporation that keeps its books on a June 30 year cannot file on a calendar year.
• A calendar year ends December 31. A fiscal year ends on the last day of any other month; December 31 cannot be called a fiscal year. Fiscal years are usually chosen to match the natural business year — the low point in the cycle.
• A personal service corporation — one whose principal activity is personal services performed substantially by its employee-owners — must use a calendar year unless it establishes a business purpose to the satisfaction of the IRS, or makes a §444 election (which comes with a required payment) (§441(i)).

Due dates and extensions

• For tax years beginning after 2015 the corporate due date is the 15th day of the fourth month after year-end (it had been the third). Calendar year: April 15.
• The one exception is the June 30 year-end, which was left on the 15th day of the third month — September 15 — for a decade. updated 2026 For tax years beginning after December 31, 2025 that exception ends: a June 30 corporation’s year beginning July 1, 2026 is due October 15, 2027. The year ending June 30, 2026 is still due September 15, 2026, with a seven-month extension to April 15, 2027.
• Extension: Form 7004, automatic. updated 2026 The course describes a five-month extension for calendar-year corporations through 2025. In practice the regulations and the Form 7004 instructions have given calendar-year C corporations six months, to October 15, since the 2016 returns; the statutory five-month figure never operated. check
• An extension extends the time to file, not to pay. Tax is due with the extension request.
• added 2026 Estimated tax is not covered in the course. A corporation expecting to owe $500 or more must pay four installments, each 25% of the required annual payment, on the 15th of the 4th, 6th, 9th and 12th months (April, June, September, December for a calendar year). The safe harbor is 100% of the prior year’s tax, but only if the prior year was a full 12 months and showed a tax liability, and a “large corporation” (taxable income of $1 million or more in any of the three prior years) may use it only for the first installment. Form 1120-W was discontinued after 2022; use the worksheet in the Form 1120 instructions and pay by EFTPS. Underpayment penalty on Form 2220.

Changing the year-end

• Requires IRS approval, requested on Form 1128. Two routes.
• Automatic approval (Rev. Proc. 2006-45, modified by Rev. Proc. 2007-64 and Rev. Proc. 2018-17): available if there is a business purpose and none of the exclusions apply. The main exclusions: a change of accounting period within the 48 months ending with the last month of the requested year; an interest in a pass-through entity or controlled foreign corporation (with exceptions); being a personal service corporation, S corporation, IC-DISC, foreign corporation, tax-exempt or cooperative; leaving a consolidated group during the year; or having a required tax year other than the one requested.
• Procedure: file Form 1128 with “FILED UNDER REV. PROC. 2006-45” at the top of page 1, by the due date including extensions of the short-period return, and attach a copy to that return. No fee. The IRS does not acknowledge it. check Confirm the current filing address and whether a successor revenue procedure has been issued; the Form 1128 instructions cite the current authority.
• Ruling request (Rev. Proc. 2002-39 and the annual Rev. Proc. 2026-1): if any exclusion applies, complete Part III of Form 1128 and file by the due date without extensions of the short-period return. There is a user fee. The IRS acknowledges within 45 days and the corporation cannot file on the new year until approved.
• The short period runs from the day after the old year ends to the new year-end, and its return is due the 15th day of the fourth month after the new year-end. Income for the short period is annualized to compute the tax.

Study questions 8–14

• SQ 8. Johnson Corp keeps accrual books on a June 30 year but wants to file on a calendar year. The IRS allows: the June 30 fiscal year. The tax year must match the books.
• SQ 9. Grace Corp incorporates August 1, 2019 and elects a July 31 year. First return due: November 15, 2020.
• SQ 10. Ace Computer Corp begins April 1, 2019 on a calendar year. First return (April 1 to December 31, 2019) due: April 15, 2020.
• SQ 11. United Corp begins March 1, 2019 and elects a June 30 year. First return covers: March 1 to June 30, 2019.
• SQ 12. Gauley Whitewater, calendar year through 2019, changes to September 30. Short-period return: January 1 to September 30, 2020.
• SQ 13. Same facts. Last day to file for automatic approval: January 15, 2021 — the due date of the short-period return.
• SQ 14. Pet Land changed to a September 30 year six years ago with IRS permission and now wants to go back to a calendar year for good business reasons. The IRS will not reject it: the prior change is outside the 48-month window and nothing else excludes automatic approval.

Private reference, not client advice. Notes taken from a 2019 continuing-education course (Thomson Reuters Checkpoint Learning, C Corporations — Overview of Corporate Income Tax); figures and rules brought current to 2026 in October 2026 (P.L. 119-21, Rev. Proc. 2024-40, Rev. Proc. 2025-32). Verify current-year amounts before relying on them.