Fiscal Year vs Calendar Year: Quarters and Who Uses Which

The definitions

The IRS calls the annual accounting period a tax year and allows two kinds:

• Calendar year: 12 consecutive months beginning January 1 and ending December 31.
• Fiscal year: 12 consecutive months ending on the last day of any month except December. A 52-53-week year is a special fiscal year, covered below.

Publication 538 says the calendar year is the most common tax year. Once you adopt one, you keep your books and report income and expenses on that same period every year.

The federal fiscal year

The federal government's fiscal year begins on October 1 and ends on September 30 of the following year. It is named for the calendar year in which it ends, so FY2027 runs from Oct 1, 2026 to Sep 30, 2027. That is why the first quarter in a federal budget report means October to December, and why a federal fiscal year number is always one higher than the calendar year it starts in.

Quarter dates side by side

A quarter is three months of the year in use. Here are the quarters for calendar 2027, federal FY2027, and a fiscal year that starts on July 1, 2026. Weekdays are Monday to Friday, before holidays.

Quarters are not equal in length. Counting days and weekdays:

A quarter with fewer weekdays has less selling and billing time, which shows up when one quarter is compared with the next. The business days calculator takes federal holidays out of any range, and the days between dates tool counts the days from a quarter's start to any deadline.

Who uses which

Anyone can generally adopt the calendar year. The IRS says you must use it if any of these apply:

• You keep no books or records.
• You have no annual accounting period.
• Your present tax year does not qualify as a fiscal year.
• A provision of the tax code or regulations requires it.

Individuals generally use the calendar year. Publication 538 lets an individual adopt a fiscal year only if he or she keeps books and records on that fiscal year. Income tax is also withheld from wages on a calendar-year basis.

Some business forms have their own limits. An S corporation must use a permitted tax year: the calendar year, a year elected under section 444, a 52-53-week year ending with reference to one of those, or a fiscal year it can show a business purpose for. Partnerships generally follow the tax years of their partners under the required tax year rules in the same publication.

A business with a busy season may want a fiscal year that ends after that season, so one season's results are not split across two returns. That is a choice, not a rule, and it has to fit the limits above.

52-53-week years

Some businesses want every year and quarter to contain whole weeks. The IRS allows a 52-53-week tax year if you keep your books on that basis. It must always end on the same day of the week, either on the last time that weekday falls in a given month or on the date of that weekday nearest to the end of the month.

Because 52 weeks are 364 days, such a year drifts a day or two against the calendar each year, and every few years it adds a 53rd week to catch up. A year that ends on the last Saturday of December:

In this table only 2028 has 53 weeks. Between 2024 and 2045 the pattern gives 53-week years in 2028, 2033, 2039, 2044. The extra week adds 1/52, about 1.9 percent, to a year's sales and costs, so compare a 53-week year with a 52-week one per week, not in totals. The week number tool shows which week of the year any date falls in.

Deadlines follow the year end

The year end sets the filing date. For individuals, the IRS lists April 15 for calendar-year filers and the 15th day of the fourth month after the fiscal year ends for fiscal-year filers. If that day falls on a weekend or legal holiday, the due date moves to the next business day.

Businesses have their own due dates by entity type, but the pattern is the same: count forward from the last day of the tax year, not from December 31. A first or last return for a period shorter than 12 months is a short tax year. Publication 538 says a short period return may be required when an entity did not exist for the whole year or changes its accounting period; a corporation formed on July 1 that picks the calendar year files its first return for July 1 through December 31.

Changing your tax year

A business that wants to switch generally needs IRS approval, requested on Form 1128. Some changes qualify for automatic approval, which needs no user fee. An S corporation that wants a year other than the calendar year uses Form 2553 instead. For a partnership, Publication 538 says the change needs a short period return covering the months between the end of the old tax year and the start of the new one.

Reading FY labels

"FY2027" means October 2026 to September 2027 for the federal government, July 2026 to June 2027 for a body with a July year that names by end year, and January to December 2027 for a calendar-year company. Before comparing two reports, check the start month of each year, and whether a year has 53 weeks. Estimated tax payments follow their own schedule, covered in the guide to estimated quarterly taxes.

Frequently asked questions

Sources

• IRS: Tax years (calendar year and fiscal year definitions, 52-53-week year, who must use a calendar year, Form 1128)
• IRS Publication 538, Accounting Periods and Methods (calendar year most common; individuals generally use the calendar year; 52-53-week year ends on the same weekday; S corporation permitted years; Form 2553)
• IRS: When to file (individual returns due April 15 for calendar-year filers, the 15th day of the fourth month after a fiscal year ends, next business day after a weekend or holiday)
• U.S. House of Representatives, Statement of Disbursements glossary: fiscal year (October 1 to September 30 of the following year)
• Congressional Research Service, via Congress.gov: each fiscal year is identified by the calendar year in which it ends (FY2011 began October 1, 2010)

General information based on the sources above, not tax, legal or financial advice.

Written by Tobias. Updated October 30, 2026.