When Does the Tax Year Start? Calendar, Fiscal, and Short Years

For individual taxpayers in the United States, the tax year starts on January 1 and ends on December 31. That 12-month window is called the calendar year, and federal law makes it the default for almost everyone who files a personal return. Businesses that keep formal books can instead adopt a fiscal year, which is any 12-month period ending on the last day of a month other than December. A third option, the 52–53 week year, always ends on the same weekday and shifts by a few days each year.

The Calendar Year Is the Default

A calendar tax year runs from January 1 through December 31. Federal law defines it as a 12-month period ending on December 31, and it is the most common reporting cycle by a wide margin.

You are required to use the calendar year if any of the following apply: you keep no books or records, you have no annual accounting period, or the accounting period you do use does not qualify as a fiscal year.¹ Because most individuals track their finances on a January-to-December cycle and receive W-2s and 1099s on that same schedule, the calendar year is the practical default for wage earners, freelancers, and small-scale investors.²

Sole proprietors report business income and losses directly on their personal returns, so their business activity automatically follows the same January-to-December cycle as their individual filing. A sole proprietor cannot adopt a separate fiscal year for the business without IRS permission.

When a Business Can Use a Fiscal Year Instead

A fiscal year is any 12-month period that ends on the last day of a month other than December. A company with a fiscal year ending June 30, for example, starts its tax year on July 1. Federal law allows any taxpayer who keeps adequate books and records to adopt a fiscal year, but restrictions apply to certain entity types.

Businesses often pick a fiscal year that lines up with their natural operating cycle. Retailers frequently choose a year ending in January so the entire holiday shopping season and post-holiday returns fall within one reporting period. Agricultural businesses may end their year after harvest. Closing the books during a slow period gives accountants more time and produces financial statements that capture a complete business cycle in a single year.¹

You establish a fiscal year by filing your first tax return covering that 12-month period. Once adopted, the fiscal year remains in effect until the IRS approves a change.

Pass-Through Entities Face Limits

Partnerships and S corporations cannot freely choose any fiscal year. Because income from these entities flows through to the owners’ personal returns, federal law generally requires them to match their owners’ tax years to prevent long delays between when income is earned and when it is taxed.

A partnership must use the tax year of partners who together own more than 50 percent of partnership profits and capital. If no single tax year meets that test, the partnership must use the tax year of all principal partners (those owning 5 percent or more). If those partners have different tax years, the partnership defaults to the calendar year. A partnership can use a different year only by proving a legitimate business purpose to the IRS, and deferring income to partners does not count as a valid reason.³

S corporations face a similar rule. An S corporation’s tax year must end on December 31 unless the corporation can demonstrate a business purpose for a different year-end. As with partnerships, deferring income to shareholders is not an acceptable reason.⁴

The 52–53 Week Variation

Some businesses use a 52–53 week tax year instead of a standard fiscal year. This variation always ends on the same day of the week, such as the last Saturday in March or the Friday nearest to June 30. Because months do not divide evenly into weeks, the actual year-end shifts slightly each year, resulting in periods that alternate between 52 and 53 weeks.¹

To adopt a 52–53 week year, you file a statement with your first tax return using that period. The statement must specify the calendar month your year references, the day of the week it always ends on, and whether it ends on the last occurrence of that weekday in the month or the occurrence nearest to the month’s final day.⁵ Switching to a 52–53 week year from an established tax year requires IRS approval.

Large retailers and manufacturers whose operations revolve around weekly sales cycles or payroll periods often use this format. It guarantees that every reporting period contains the same number of weekdays, which makes year-over-year comparisons more consistent.

Short Tax Years: When the Start Date Shifts

A short tax year is any reporting period covering fewer than 12 months. Two common situations create one: a new entity that starts mid-year, or a change in accounting period.

When a business forms partway through the year, say it incorporates on May 15 and adopts a calendar year, the first tax year runs only from May 15 through December 31. The reverse applies too: if a corporation dissolves or a taxpayer dies, the tax year ends on that date rather than at the normal year-end.² For a deceased individual, the final tax year runs from January 1 to the date of death, and the estate then begins its own separate tax year the following day.

A short tax year also arises when you change from one annual accounting period to another. Switching from a June 30 fiscal year to a calendar year, for example, creates a short period from July 1 through December 31.

Because tax brackets are designed around a full 12-month year, the IRS requires you to annualize income for a short period. You multiply taxable income for the short period by 12 and divide by the number of months in that period to get an annualized figure, compute the tax on that annualized amount, then take the fraction of that tax that corresponds to the short period’s length.⁶

How the Start Date Sets Your Filing Deadline

Your tax year determines when your return is due. Missing the deadline triggers a failure-to-file penalty of 5 percent of unpaid tax for each month the return is late, up to a maximum of 25 percent.⁷

Individual calendar-year returns are due April 15 following the end of the tax year. Filing Form 4868 gives you an automatic extension to October 15, but any taxes owed are still due April 15.⁸
Partnership returns (Form 1065) are due on the 15th day of the 3rd month after the tax year ends. For a calendar-year partnership, that is March 15. A six-month extension is available on Form 7004.⁹
S corporation returns (Form 1120-S) are also due on the 15th day of the 3rd month after year-end, which is March 15 for calendar-year filers.⁹
C corporation returns (Form 1120) are due on the 15th day of the 4th month after year-end, or April 15 for calendar-year corporations. Form 7004 provides a six-month extension.⁹

If any deadline lands on a Saturday, Sunday, or legal holiday, the due date shifts to the next business day. Fiscal-year filers follow the same formulas by counting the specified number of months from their own year-end.

Once Set, Your Tax Year Cannot Easily Change

Once you establish a tax year by filing your first return, you cannot switch to a different period without IRS approval. Partnerships, S corporations, personal service corporations, and certain trusts may qualify for automatic approval under a streamlined IRS procedure, with no user fee for automatic changes.¹⁰ To qualify, the entity generally must meet specific conditions, such as adopting its required tax year or changing to a natural business year supported by its revenue pattern.

Taxpayers who do not qualify for automatic approval must file Form 1128, Application to Adopt, Change, or Retain a Tax Year. The application requires detailed information about your current accounting methods, gross receipts history, and reasons for the requested year-end. The IRS will deny the request if the change would significantly distort income or create an inappropriate deferral of tax.²

1
Office of the Law Revision Counsel. 26 USC 441 – Period for Computation of Taxable Income
2
Internal Revenue Service. Tax Years
3
Office of the Law Revision Counsel. 26 USC 706 – Taxable Years of Partner and Partnership
4
Office of the Law Revision Counsel. 26 USC 1378 – Taxable Year of S Corporation
5
eCFR. 26 CFR 1.441-2 – Election of Taxable Year Consisting of 52-53 Weeks
6
Office of the Law Revision Counsel. 26 USC 443 – Returns for a Period of Less Than 12 Months
7
Internal Revenue Service. Failure to File Penalty
8
Internal Revenue Service. When to File
9
Internal Revenue Service. Publication 509 (2026), Tax Calendars
10
Internal Revenue Service. Revenue Procedure 2006-46