Ask a model when Q1 ends and it will tell you 31 March, because that is what a calendar-year fiscal year implies and that is the majority answer in its training data. For a US federal agency, a Japanese company, an Australian business or an Indian taxpayer, it is wrong by one to two quarters.
The calendar-year default
A large number of countries do run the fiscal year from 1 January to 31 December — China, Germany, France, the Netherlands, Spain, Brazil, Russia, Switzerland and most of the euro area among them. That is why the default is usually right, and why the exceptions are so easy to miss: nothing in the output announces that an assumption was made.
Ireland is the case that shows this is a legislative choice rather than a fact of nature. The Irish tax year ran 6 April to 5 April, inherited from the UK, until it was moved to the calendar year with a transitional short year running from 6 April to 31 December 2001. Anything in a historical dataset from before that change is on the old basis.
Who starts when
The four common start months are January, April, July and October. Where a country has different years for government accounts and for personal tax — which is normal, not exceptional — both are given.
1 January China, Germany, France, Netherlands, Spain,
Brazil, Russia, Switzerland, Ireland (since 2002)
1 April United Kingdom (government financial year; personal
tax year runs 6 April - 5 April)
India, Japan, Canada (federal government),
Hong Kong, Singapore (government),
South Africa (government; personal tax year
runs 1 March - end February),
New Zealand (personal tax year)
1 July Australia, Egypt, Pakistan,
New Zealand (Crown financial year)
1 October United States (federal government),
Thailand (government)
The sources for the four largest of these are worth naming, because they are each set by an instrument rather than by custom. The US federal fiscal year has run from 1 October since fiscal year 1977, set by the Congressional Budget and Impoundment Control Act of 1974 and codified at 31 U.S.C. § 1102; the US Government Accountability Office uses that basis throughout its reporting. The UK personal tax year of 6 April to 5 April is documented by HMRC on GOV.UK. The Australian income year of 1 July to 30 June is documented by the Australian Taxation Office. India’s 1 April to 31 March year is the basis of the Union Budget and of the Income-tax Act’s “previous year”.
Fiscal years are changed by legislation and the change is not always well signposted internationally — Ireland moved, and proposals to move have been raised in several other countries. Verify against the country’s revenue authority or finance ministry before relying on a row of this table for anything with money attached, and treat any copy of it more than a year old as unverified.
FY2026 means two different years
This is the part the tables leave out, and it causes more damage than the start months do. Once a fiscal year spans two calendar years, somebody has to decide which one names it, and countries decided differently.
United States FY2026 = 1 Oct 2025 - 30 Sep 2026 named for the END year
Japan 令和7年度 = 1 Apr 2025 - 31 Mar 2026 named for the START year
Australia FY2026 = 1 Jul 2025 - 30 Jun 2026 named for the END year
(usually written 2025-26)
India FY 2025-26 = 1 Apr 2025 - 31 Mar 2026 written as a span
United Kingdom "the 2025 to 2026 tax year" written as a span
The US and Japanese conventions are exact opposites, and both are written as a single year. A Japanese fiscal year is 年度 (nendo) and is numbered by the imperial era year in which it starts — the year beginning April 2025 is 令和7年度, Reiwa 7, because April 2025 fell in Reiwa 7. So “FY26” from a US federal source and “令和8年度” from a Japanese one refer to periods that overlap by six months and are not the same year. The era-year arithmetic is a second conversion on top of the fiscal one.
Australia and the UK both hedge by writing the span, which is why Australian reporting says 2025-26 rather than 2026 in formal contexts — although “FY26” is used colloquially there for the year ending 30 June 2026, matching the US direction. When a model produces “FY2026” without a country, the string carries no recoverable meaning.
India has a second, offset label
India adds a distinction that catches out anyone reading Indian tax material for the first time. The financial year (FY) is when the income is earned; the assessment year (AY) is the following year, when it is assessed and the return is filed.
income earned 1 Apr 2025 - 31 Mar 2026
financial year FY 2025-26
assessment year AY 2026-27
Both are written in the same two-year span format and they differ by one year. Indian tax forms, portals and guidance ask for one or the other explicitly, and a generated form filled with the financial year where the assessment year was asked for is a filing error rather than a cosmetic one. The related lakh and crore number grouping appears on the same documents.
Companies choose their own
National fiscal years bind governments and, usually, personal taxation. Corporate fiscal years are frequently something else entirely, chosen to end at a quiet point in the business: software companies commonly end in June, and retailers commonly end in late January, after the holiday season and the returns that follow it have closed.
Retailers add a further wrinkle: many use a 52- or 53-week fiscal calendar rather than a calendar-month one, so that each quarter contains the same number of weekends and year-on-year comparisons are meaningful. The widely used 4-5-4 pattern is published by the National Retail Federation. Such a year ends on a fixed weekday rather than a fixed date, which means it has 53 weeks roughly every fifth or sixth year and one quarter in that year is 14 weeks long. Any year-on-year comparison across a 53-week year that does not adjust for the extra week is overstating growth by roughly the value of one week.
Handling this in generated output
- Never store or emit a bare fiscal year label. Store the start date and the end date. A label is a rendering of that pair for a particular audience, and it is not reversible without knowing whose convention produced it.
- Put the country or the entity next to the label wherever it appears: “US FY2026 (Oct 2025 – Sep 2026)”. The parenthetical is short and it removes every ambiguity on this page at once.
- Do not let a model infer the fiscal year from a date. Ask it for the calendar date, and derive the fiscal period in code from a configured start month and a configured labelling direction. Those are two settings, and a model asked for the label will silently supply both from whichever convention dominated its training data.
- Check the boundary quarters in tests. Any fiscal-period function that is wrong is wrong for dates in the month of the boundary; the middle of the year exercises nothing.
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