What Is a Fiscal Year? Definition, Examples, and Deadlines

A fiscal year is any twelve-month accounting period that ends on the last day of a month other than December. Businesses, government agencies, and nonprofits pick fiscal years that match their natural operating rhythms instead of following the January-through-December calendar most individuals use. The IRS treats a fiscal year as a formal tax year, so the choice shapes filing deadlines, estimated payments, and how income gets reported.¹

Fiscal Year vs. Calendar Year

A calendar year always runs January 1 through December 31. A fiscal year can end on the last day of any month except December. A company whose fiscal year runs April 1 through March 31, for example, closes its books each spring instead of each winter.¹

The IRS also recognizes a 52-53 week variant. That version ends on the same day of the week each year (say, the last Saturday in March) and fluctuates between 52 and 53 weeks instead of landing on the last calendar day of a month.²

Most individuals and many small businesses use a calendar year because it keeps personal and business taxes on the same cycle. You adopt a tax year by filing your first income tax return using that period, and once you’ve filed a calendar-year return, you’re locked into it unless the IRS approves a change or you qualify for an exception.²

How Fiscal Years Are Named

The standard convention names a fiscal year after the calendar year in which it ends. A company whose fiscal year runs October 1, 2025, through September 30, 2026, calls that period Fiscal Year 2026. This holds across government, higher education, and most corporate reporting. The federal government’s current fiscal year began October 1, 2025, and runs through September 30, 2026, so it’s FY 2026.³

One wrinkle catches people off guard. The IRS uses the year a fiscal year begins for form selection. A corporation with a fiscal year starting in 2025 and ending in 2026 files the 2025 version of Form 1120, not the 2026 version. The period is still called FY 2026 for reporting purposes, but the tax form matches the year the period started.

Common Fiscal Year Examples

The Federal Government

The United States federal government operates on a fiscal year running October 1 through September 30. That timing gives Congress the summer months to work through appropriation bills before the new budget period starts in the fall.³

Schools and Nonprofits

Schools and many nonprofits favor a July 1 through June 30 fiscal year, which tracks the academic calendar and keeps a school year inside a single reporting period. About 22 percent of public charities use a June 30 fiscal year end, and those organizations hold a disproportionate share of total nonprofit assets.⁴ A summer camp might close its books in winter after wrapping up its core programming, which is why nonprofit fiscal years end in nearly every month.

Retailers

Retailers often end their fiscal year on January 31 or use a 4-5-4 calendar that divides the year into repeating four-week and five-week periods. The logic is straightforward. The holiday shopping season and post-holiday returns dominate December and early January, so closing the books in late January captures the entire peak as one clean period rather than splitting it across two fiscal years. The 4-5-4 format has been a voluntary industry standard since the 1940s and also keeps week-over-week sales comparisons consistent from year to year.

Who Can and Can’t Choose a Fiscal Year

Not everyone gets to pick. The IRS requires you to use a calendar year if you keep no books or records, have no annual accounting period, or fall under a tax code provision that mandates it.² Sole proprietors who filed their first personal return on a calendar-year basis have to stick with it for their business too, unless the IRS approves a change.

Personal service corporations face a stricter rule. Federal law requires them to use a calendar year unless they can prove a legitimate business purpose for a different period, and simply deferring income to shareholders doesn’t count.¹ S corporations face the same restriction under a separate statute.⁵

Partnerships don’t get free rein either. Federal law ties a partnership’s tax year to the tax years of its partners, mainly to prevent income deferral. If partners holding more than 50 percent of profits and capital all share the same tax year, the partnership must use that year. If no such majority exists, the partnership must use the tax year of all principal partners (those with 5 percent or more of profits or capital). If neither test produces an answer, the partnership defaults to a calendar year.⁶ Since most individual partners use a calendar year, most partnerships end up on one too.

Partnerships, S corporations, and personal service corporations that can’t otherwise justify a non-calendar year have one more option: a Section 444 election, which allows a fiscal year with a deferral period of up to three months. The election comes with a required payment or deduction limitation designed to offset the deferral benefit, so it only makes sense when a non-calendar year offers a clear operational advantage.⁷

How Filing Deadlines Shift

Your fiscal year end date drives every tax deadline. The math for the most common entity types:

Individuals: return due on the 15th day of the fourth month after the fiscal year ends.⁸
C corporations: return due on the 15th day of the fourth month after the fiscal year ends. One exception: corporations with a June 30 fiscal year end must file by the 15th day of the third month.⁹
Partnerships: return due on the 15th day of the third month after the fiscal year ends.¹⁰
Tax-exempt organizations with a June 30 year end: Form 990 due November 15.⁴

Corporate estimated tax payments follow their own rhythm: the 15th day of the 4th, 6th, 9th, and 12th months of the fiscal year.¹⁰ Any deadline that falls on a weekend or legal holiday moves to the next business day. Most entities can request a six-month extension by filing Form 7004 before the original deadline, though an extension gives you more time to file, not more time to pay.¹¹

Adopting or Changing a Fiscal Year

You adopt a fiscal year by filing your first tax return using that period. Switching afterward requires IRS approval on Form 1128 (Application to Adopt, Change, or Retain a Tax Year).¹² Some changes qualify for automatic approval at no cost; others require a private letter ruling with a $1,500 user fee and evidence that the new fiscal year serves a genuine business purpose beyond deferring income.¹³

A change also creates a short tax year, the gap between the old fiscal year’s end and the new one’s start. You file a separate return for that period, and the IRS annualizes your income for the calculation, which can push you into higher brackets than your actual income warrants.¹⁴ Timing a switch matters for that reason alone.

1
Office of the Law Revision Counsel. 26 USC 441 – Period for Computation of Taxable Income
2
Internal Revenue Service. Tax Years
3
USAGov. The Federal Budget Process
4
Internal Revenue Service. Return Due Dates for Exempt Organizations: Annual Return
5
Office of the Law Revision Counsel. 26 USC 1378 – Taxable Year of S Corporation
6
Office of the Law Revision Counsel. 26 USC 706 – Taxable Years of Partner and Partnership
7
U.S. Code. 26 USC 444 – Election of Taxable Year Other Than Required Taxable Year
8
Internal Revenue Service. When to File
9
Internal Revenue Service. Starting or Ending a Business 3
10
Internal Revenue Service. Publication 509 (2026), Tax Calendars
11
IRS. Instructions for Form 7004 (Rev. December 2025)
12
eCFR. Part 1 – Income Taxes – Accounting Periods
13
IRS. Schedule of IRS User Fees
14
eCFR. 26 CFR 1.443-1 – Returns for Periods of Less Than 12 Months