A tax year is the annual accounting period whose income and expenses you report on a tax return. For most individuals in the United States, it is the calendar year, January 1 through December 31. The tax year decides which transactions belong on a return. The filing deadline is a separate date, and the two are often confused.
This guide covers U.S. federal rules as described by the Internal Revenue Service (IRS). State, local, and non-U.S. tax systems can use different periods, so check with the relevant tax authority if you are subject to one.
How the IRS defines a tax year
The IRS describes a tax year as an annual accounting period for keeping records and reporting income and expenses. You use it to work out taxable income. Think of it as the bookkeeping window: money earned and spent inside that window is reported on the return for that window, no matter when the return is actually sent in. The IRS explains the term on its “Tax years” page on IRS.gov.
The three types of tax year
| Type | Period covered | Who typically uses it | Key condition |
|---|---|---|---|
| Calendar tax year | 12 consecutive months, January 1 through December 31 | Most individuals; many businesses | The default period for individuals |
| Fiscal tax year | 12 consecutive months ending on the last day of a month other than December; IRS guidance also recognizes a 52- or 53-week year that need not end on a month’s last day | Eligible businesses; individuals only if they keep their books and records on that basis | Must meet IRS eligibility rules |
| Short tax year | Fewer than 12 months | Taxable entities that do not exist for an entire tax year, or that change their accounting period | Arises only in these specific circumstances |
Fiscal year versus the federal government’s fiscal year
A business fiscal tax year is not the same thing as the federal government’s fiscal year. The IRS glossary defines the government’s fiscal year as running from October 1 of the previous calendar year through September 30 of the year it is named for. A fiscal tax year is chosen by a taxpayer and can end in any month except December, subject to the rules above.
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Who uses which tax year
Individuals
Individuals generally use the calendar year. IRS Publication 538 (Accounting Periods and Methods) says an individual can use a fiscal year only if the individual maintains books and records on that basis. In practice, most individual filers never make a choice; their tax year is simply the calendar year.
Businesses
Businesses may use a calendar year or an eligible fiscal year. Some entity types are subject to required-year rules that limit their choice, so check the rules for your entity type in Publication 538 and the instructions for your return before choosing.
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How a business adopts its tax year
According to IRS guidance, a business generally adopts a tax year by filing its first income tax return using that period. The following steps reflect that guidance:
- Confirm whether your entity type is required to use a particular tax year. Review Publication 538 and the instructions for the return you will file.
- Choose a period that matches how your books are kept, and make sure it is eligible for your entity type.
- Adopt the year by filing your first income tax return using that period. Filing an extension request, applying for an employer identification number (EIN), or paying estimated taxes does not, by itself, adopt a tax year.
- If you already have an adopted tax year and want to change it, you generally need IRS approval. Request it on Form 1128, subject to the exceptions described in IRS guidance and the form’s instructions.
Tax year versus filing date
The tax year is the period whose income and expenses are reported. The filing date is the deadline for submitting the return. A return filed in 2026 can cover a 2025 tax year, so the two dates do not match.
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Publication 509 (Tax Calendars) lists April 15, 2026, as the filing date for calendar-year individual filers. That date applies to the return covering calendar 2025. For fiscal-year filers, the general rule in Publication 509 is the 15th day of the fourth month after the fiscal year ends, adjusted for weekends and holidays. Some entity types have different due dates, so confirm the rule for your form.
| Tax year | Period reported | Filing date under the general rule |
|---|---|---|
| Calendar year 2025 (individual) | January 1, 2025, through December 31, 2025 | April 15, 2026, as listed in Publication 509 (2026) |
| Fiscal year ending June 30, 2026 | July 1, 2025, through June 30, 2026 | October 15, 2026, under the general fiscal-year rule; entity-specific dates may differ |
Deadlines are set each year and can be changed by special relief, so confirm the current IRS calendar before you file.
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Common points of confusion
- The year you file is not automatically your tax year. Returns filed in 2026 usually report a prior tax year.
- The federal government’s fiscal year is not a business tax year. It runs October 1 through September 30 (IRS glossary).
- A short tax year is not a planning choice. It arises only when an entity does not exist for a full year or changes its accounting period.
- State tax years may differ. Check your state revenue agency for its own period and deadlines.
Limits of this guide
- This guide summarizes IRS guidance, including Publication 538, which was last revised in January 2022. Check the IRS website for later changes before applying its detailed rules.
- Publication 509 deadlines apply to the years they name. Earlier or later years may have different dates.
- This guide does not determine whether a particular taxpayer is eligible for a given accounting period or an exception to a required-year rule. Those questions depend on the facts of each case and may require a qualified tax professional.
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