Tax Year

What Is a Tax Year?

A tax year (also called a fiscal year or assessment year) is the 12-month period over which income is measured, tax is calculated, and returns are filed. Not all countries use the calendar year (January–December) — and the differences have real consequences for international workers, expats, and anyone moving countries mid-year.

Tax Year Dates by Country

Country	Tax Year	Filing Deadline
United States	1 Jan – 31 Dec	15 April (extensions available)
United Kingdom	6 April – 5 April	31 January (online) / 31 October (paper)
India	1 April – 31 March (Financial Year)	31 July (for non-audit cases)
Canada	1 Jan – 31 Dec	30 April (30 June for self-employed)
Australia	1 July – 30 June	31 October (or later via tax agent)
New Zealand	1 April – 31 March	7 July (or via tax agent, up to 31 March following year)
Ireland	1 Jan – 31 Dec	31 October (ROS: 15 November)
Singapore	1 Jan – 31 Dec	15 April (online) / 18 April (e-filing)
South Africa	1 March – 28/29 February	October/November (eFiling)

Why the Dates Differ

The UK’s unusual 6 April start date is a historical quirk dating to the 1752 calendar reform. When Britain switched from the Julian to the Gregorian calendar (losing 11 days), the Treasury refused to lose 11 days of tax revenue and shifted the fiscal year end from 25 March (Lady Day) to 5 April — which then became 6 April the following year. That date has persisted ever since.

India’s April–March financial year aligns with its colonial inheritance from British administration (which historically used a similar structure before Britain’s own calendar shifted).

South Africa’s March–February year is distinctive among major economies and creates complexity for South Africans working internationally.

Financial Year vs Assessment Year (India)

India uses two terms that frequently cause confusion:

• Financial Year (FY): The year in which income is earned. FY 2026-27 runs from 1 April 2026 to 31 March 2027.
• Assessment Year (AY): The year in which income is assessed (i.e., when you file your tax return for the preceding FY). AY 2027-28 is when you file for FY 2026-27.

When an Indian tax document says “AY 2027-28” it refers to income earned in FY 2026-27 (1 April 2026 – 31 March 2027).

Split-Year Treatment for Movers

When you arrive in or depart from a country during the tax year, most jurisdictions have rules to ensure you only pay tax as a resident for the portion of the year you were actually resident.

United Kingdom: The Statutory Residence Test has eight “split year” cases. When you qualify, HMRC splits the tax year into a UK part (when you are resident) and an overseas part (when you are not). You pay UK tax only on income earned or arising in the UK part.

Australia: The ATO splits the year from/to the date you become or cease to be an Australian tax resident. The tax-free threshold is prorated — you only receive a fraction of the $18,200 threshold if you were not resident for the full year.

United States: The US does not have a formal split-year provision. If you are a non-resident alien for part of the year and a resident alien for the remainder (e.g., you arrived on a work visa and met the Substantial Presence Test), you may file as a “dual-status alien” — which involves special rules and restrictions on deductions and filing status.

New Zealand: The IRD treats you as resident from the first day you established a “permanent place of abode” in New Zealand, or from the 183rd day of presence if you did not have a permanent abode established earlier.

Tax Year and Payroll Timing

For employees, the tax year determines:

• When to submit withholding declarations / Forms W-4 (US), P46 (UK), etc.
• When your employer resets withholding calculations
• When year-end forms (W-2, P60, Form 16) are issued

Key UK payroll point: HMRC issues tax codes at the start of each tax year (6 April). A new starter without a P45 may be given an emergency tax code (which assumes they have used all their personal allowance), leading to temporary over-withholding.

Tax Year and Investment Decisions

Knowing the tax year boundaries helps with:

• Timing capital asset disposals within or across years to split gains
• Pension contribution deadlines (e.g., UK ISA allowance resets each 6 April)
• India Section 80C investments — must be made within the financial year (by 31 March) to count for that year’s deductions
• Australia superannuation contributions — concessional cap is measured per tax year (1 July – 30 June)

Key Takeaway

Tax years differ meaningfully across countries — from the US and Canada’s clean calendar year to the UK’s 6 April anomaly and India’s April–March financial year. If you move countries, receive foreign income, or manage investments across jurisdictions, understanding which year’s income is assessed when — and how filing deadlines interact — is essential for staying compliant and avoiding late penalties.