What Is a Fiscal Year? Eligibility, Deadlines, and Changes

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 some individuals use one to track income, expenses, and tax obligations on a cycle that fits their operations instead of the standard January-through-December calendar. Federal tax law decides who is allowed to use a fiscal year, and once adopted, it generally sticks unless the IRS approves a change.

Fiscal Year vs. Calendar Year

A calendar year always runs January 1 through December 31. A fiscal year can start on the first day of any month and end twelve months later, as long as it ends on the last day of a month other than December.¹ April 1 through March 31 is a fiscal year. So is July 1 through June 30. An entity can also elect a 52-to-53-week year that always ends on the same day of the week nearest a chosen month-end, which some large companies use to keep every reporting period the same length.

The practical effect is a shift in what “the year” means for the entity. A business with a fiscal year ending March 31 calls April through June its first quarter, even though those months fall in the calendar year’s second quarter. Financial statements close on a different date, annual meetings move, and quarterly reporting shifts along with them.

Who Can Use a Fiscal Year

The rules turn on entity type, and the flexibility varies a lot.

C-Corporations

Regular C-corporations have the widest choice. A C-corporation adopts a fiscal year simply by filing its first income tax return using that period, and must then keep using it consistently unless the IRS approves a change.²

Individuals and Sole Proprietors

Most individuals and sole proprietors are required to use the calendar year. You must use a calendar year if you keep no books, have no annual accounting period, or your current period does not qualify as a fiscal year.¹ If you already filed your first individual return on a calendar-year basis and later start a sole proprietorship, you have to keep using the calendar year unless the IRS approves a switch.²

S-Corporations

An S-corporation must use a “permitted year,” which generally means the calendar year. A fiscal year is available only if the corporation can show a legitimate business purpose to the IRS, and deferring income to shareholders does not qualify.³

Partnerships

A partnership generally has to match the tax year of partners who own more than 50 percent of profits and capital. If no majority interest shares a common year, the partnership uses the year of all principal partners (those owning 5 percent or more). If that also fails, it defaults to the calendar year.⁴

Personal Service Corporations

A personal service corporation, generally one where employee-owners perform services in fields like health, law, accounting, engineering, or consulting, must also use the calendar year. The same business-purpose exception applies, and again, income deferral to shareholders does not count.¹

The Section 444 Election

Partnerships, S-corporations, and personal service corporations that would otherwise be locked into a calendar year can elect a fiscal year under Section 444, but only if the chosen year creates a deferral of three months or less.⁵ Partnerships and S-corporations making this election have to make annual required payments to the IRS that approximate the tax benefit of the deferral, computed from base-year income and the highest individual tax rate.⁶

How a Fiscal Year Gets Adopted

If your entity type allows one, adoption is simple: you file your first income tax return using the fiscal year you want. Filing an extension, applying for an employer identification number, or paying estimated taxes does not adopt a tax year. Only the return does.² From that point on, you have to keep your books on the same basis and report income and expenses for that period every year.⁷

How Your Fiscal Year Sets Your Filing Deadlines

Federal deadlines run off your year-end. Corporations generally file Form 1120 by the fifteenth day of the fourth month after the fiscal year ends.⁸ For a fiscal year ending March 31, that puts the deadline on July 15. Individual fiscal-year filers follow the same fourth-month rule for Form 1040.⁹

C-corporations with a June 30 fiscal year-end previously had an earlier deadline, the fifteenth day of the third month, or September 15. That exception is being phased out and no longer applies to tax years beginning on or after January 1, 2026. After that, every C-corporation files by the fifteenth day of the fourth month regardless of when its fiscal year closes.¹⁰

Missing the deadline carries a failure-to-file penalty of 5 percent of the unpaid tax per month or partial month, capped at 25 percent. For returns due in 2026, the minimum penalty when a return is more than 60 days late is the lesser of the tax owed or $525.⁸

Common Fiscal Year Cycles

The federal government runs on a fiscal year from October 1 through September 30. Congress passes appropriations each year to fund operations for that period, and the federal budget is organized around it.¹¹

Public schools and universities commonly use July 1 through June 30, which lines the reporting period up with the academic year. Many large retailers close their books on January 31, giving them room to process holiday returns, run inventory, and capture the peak shopping season before the year ends. These are industry conventions rather than legal requirements. The idea is to group a full cycle of the entity’s core activity inside one reporting window.

Changing Your Fiscal Year Later

Switching to a different fiscal year after adoption is a bigger undertaking. You generally have to file Form 1128 and either qualify for automatic approval or submit a ruling request to the IRS.⁷ Automatic approval covers a narrow set of situations, such as a newly married spouse changing to the other spouse’s accounting period (no Form 1128 required) and a subsidiary joining an affiliated group that files a consolidated return.¹²

For most other changes, you need to show a substantial business purpose. The IRS charges a user fee of $5,750 for Form 1128 requests received after January 29, 2026.¹³ Between the fee and the paperwork, picking the right fiscal year at the outset matters.

Short Tax Years

A short tax year is any tax period shorter than twelve months. Two situations create one: the entity did not exist for the full year (formed or dissolved mid-year), or the entity changed its accounting period.² You file a return covering only the shortened period, generally under the same rules as a full-year return ending on the last day of the short period. When the short year comes from a change in accounting period, income may need to be annualized, meaning you project it over twelve months to set the tax rate and then prorate the tax back to the actual period.

1
Office of the Law Revision Counsel. 26 U.S. Code 441 – Period for Computation of Taxable Income
2
Internal Revenue Service. Tax Years
3
Office of the Law Revision Counsel. 26 U.S. Code 1378 – Taxable Year of S Corporation
4
Office of the Law Revision Counsel. 26 U.S. Code 706 – Taxable Years of Partner and Partnership
5
Office of the Law Revision Counsel. 26 U.S. Code 444 – Election of Taxable Year Other Than Required Taxable Year
6
Office of the Law Revision Counsel. 26 U.S. Code 7519 – Required Payments for Entities Electing Not to Have Required Taxable Year
7
Internal Revenue Service. Publication 538, Accounting Periods and Methods
8
Internal Revenue Service. Instructions for Form 1120 (2025), U.S. Corporation Income Tax Return
9
Internal Revenue Service. Publication 509 (2026), Tax Calendars
10
eCFR. 26 CFR 1.6072-2 – Time for Filing Returns of Corporations
11
USAGov. The Federal Budget Process
12
eCFR. 26 CFR 1.442-1 – Change of Annual Accounting Period
13
Internal Revenue Service. Internal Revenue Bulletin 2026-01