What Is 31 March

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Last updated: April 15, 2026

Quick Answer: 31 March is the 90th day of the year in the Gregorian calendar (91st in leap years), with 275 days remaining until year-end. It marks historical events such as the end of the UK's financial year and the 2002 Commonwealth Games opening in Manchester.

Key Facts

31 March falls on the 90th day of the year, or 91st in leap years like 2020 and 2024.
The UK’s financial year ends on 31 March, a date set by HM Revenue and Customs.
The 2002 Commonwealth Games opened in Manchester on 31 March, lasting 10 days.
NASA launched the Fermi Gamma-ray Space Telescope on 31 March 2008.
In 1976, Cambodia adopted a new constitution on 31 March, establishing Democratic Kampuchea.

Overview

31 March is the 90th day of the year in the Gregorian calendar, with 275 days remaining until the end of the year. In leap years, such as 2020 and 2024, it falls on the 91st day, shifting the calendar dynamics slightly.

This date holds significance across various domains including finance, sports, and space exploration. Its recurring position near the end of the first quarter makes it a key marker for fiscal and academic cycles.

Financial Year-End: In the United Kingdom, 31 March marks the official end of the government’s fiscal year, used by HMRC for tax calculations and budget reporting.
Sports History: The 2002 Commonwealth Games officially opened in Manchester on 31 March, drawing over 3,800 athletes from 72 nations.
Space Missions: NASA launched the Fermi Gamma-ray Space Telescope on 31 March 2008, designed to study high-energy gamma rays from cosmic sources.
Historical Events: On 31 March 1976, Cambodia adopted a new constitution, establishing Democratic Kampuchea under the Khmer Rouge regime.
Climate Observations: The Arctic sea ice typically reaches its annual maximum extent around late March, often near 31 March, averaging 15.1 million km² in recent decades.

How It Works

Understanding the role of 31 March requires examining its function in institutional, historical, and astronomical contexts. The date serves as a recurring benchmark across multiple systems.

Gregorian Calendar: The Gregorian system places 31 March as the 90th day, with leap years adding a day to February, shifting the count to 91st.
Fiscal Policy: The UK’s tax year ends on 31 March, a legacy of pre-1752 calendar reforms when the new year began on 25 March.
Academic Cycles: Many international schools and universities use 31 March as a deadline for term-end assessments or scholarship applications.
Historical Milestones: On 31 March 1968, U.S. President Lyndon B. Johnson announced he would not seek re-election, altering the course of American politics.
Environmental Cycles: The vernal equinox occurs around 20 March, making 31 March a period of rapidly increasing daylight in the Northern Hemisphere.
Corporate Reporting: Multinational corporations often use 31 March as a quarter-end for financial reporting, especially in Asia-Pacific regions like Japan and India.

Comparison at a Glance

Comparing 31 March across different years and systems reveals patterns in policy, nature, and human activity.

Year	Event	Location	Significance
2024	End of UK financial year	United Kingdom	HMRC deadlines for self-assessment tax returns and corporate filings.
2008	Fermi Gamma-ray Telescope launch	Cape Canaveral, USA	Revolutionized high-energy astrophysics with decade-long mission.
2002	Commonwealth Games opening	Manchester, UK	Hosted 3,800 athletes from 72 Commonwealth nations.
1976	Democratic Kampuchea constitution	Phnom Penh, Cambodia	Established Khmer Rouge rule, leading to widespread atrocities.
1968	Johnson’s non-re-election announcement	Washington, D.C., USA	Shifted Vietnam War policy and Democratic Party dynamics.

The table highlights how 31 March has marked pivotal moments in governance, science, and human rights. While some events are annual, others are irreversible historical turning points.

Why It Matters

31 March is more than a calendar date—it reflects institutional rhythms and historical turning points. Its recurrence underscores the interplay between timekeeping and societal function.

Tax Compliance: In the UK, missing the 31 March deadline can result in penalties from HMRC for late corporate or personal tax filings.
Scientific Research: The Fermi Telescope has collected over 15 years of gamma-ray data, helping map black holes and supernovae.
Historical Memory: Cambodia’s 31 March 1976 constitution is studied in human rights courses as a case of totalitarian legal frameworks.
Sports Legacy: The 2002 Commonwealth Games boosted Manchester’s infrastructure, with £300 million invested in sports facilities.
Climate Indicators: Arctic ice extent near 31 March is monitored as a climate change indicator, with 2023 levels 1.2 million km² below the 1981–2010 average.
Corporate Strategy: Japanese firms often finalize fiscal year budgets by 31 March, influencing Q1 economic forecasts in Asia.

From tax returns to space launches, 31 March serves as a quiet but critical junction in global systems. Its consistent recurrence makes it a reliable marker for planning, reflection, and historical analysis.