Leap year is a calendar year with an extra day—February 29—added to keep the calendar aligned with Earth’s orbit around the Sun. In the Gregorian calendar (used as the civil calendar in most countries), leap years follow a specific rule set based on divisibility by 4, 100, and 400.
Quick facts
- Rule (Gregorian): Years divisible by 4 are leap years—except century years unless divisible by 400. (U.S. Naval Observatory)
- Why it exists: A tropical year averages about 365.24219 days, not 365. (NIST)
- Next Leap Day: February 29, 2028. (timeanddate.com)
- Leap Day odds: About 1 in 1,461 chance of being born on Feb 29. (HISTORY)
On this page:
- What is a leap year?
- Leap year rule (Gregorian)
- Why do we have leap years?
- History: Julian to Gregorian
- Leap Day dates and “leaplings”
- Traditions and folklore
- Methodology
- Sources & references
What is a leap year?
A leap year is a year with 366 days instead of 365, created by adding February 29 to the calendar. The goal is to keep dates and seasons aligned over time. (U.S. Naval Observatory)
Which years are leap years?
Gregorian leap year rule: A year is a leap year if it is divisible by 4, except years divisible by 100 are not leap years, unless they are also divisible by 400.
- Leap years: 2024, 2028, 2032, 2036 …
- Not leap years (century exceptions): 1700, 1800, 1900, 2100 …
- Leap years (century allowed): 1600, 2000, 2400 …
Source: U.S. Naval Observatory
Why do we have leap years?
Because Earth’s orbit doesn’t fit evenly into 365-day years. NIST notes the solar (tropical) year is about 365.24219 days, so without leap years, the calendar would drift away from the seasons over time. (NIST)
Who created leap years? A quick history
Julian calendar (45 BCE): Julius Caesar introduced a reform that added an extra day roughly every four years to keep the Roman calendar aligned with the solar year. (timeanddate.com)
Gregorian calendar (1582): Pope Gregory XIII introduced the Gregorian reform to correct drift caused by the Julian system’s slightly-too-long year. The Gregorian system keeps most 4-year leap days but skips certain century years. (NIST)
Leap Day dates and “leaplings”
Next Leap Day:
Tuesday, February 29, 2028. (timeanddate.com)
Recent and upcoming Leap Days (selected):
- 2020 — Saturday, Feb 29
- 2024 — Thursday, Feb 29
- 2028 — Tuesday, Feb 29
- 2032 — Sunday, Feb 29
Source: timeanddate.com
Odds of being born on Leap Day:
About 1 in 1,461. (HISTORY)
Estimated number of people born on Feb 29 worldwide:
Commonly cited estimates are around 5 million globally. (HISTORY)
Name for people born on Leap Day:
Leaplings (also commonly “leapers”). (timeanddate.com)
Traditions and folklore
Leap Day proposals: A well-known tradition says women may propose marriage on Feb 29. This is generally treated as folklore with versions linked to Ireland and Scotland/England in later retellings. (Condé Nast Traveler)
Methodology
- Authority-first: Calendar rules and year length use scientific/government sources (U.S. Naval Observatory, NIST).
- No speculation: This page uses reported or explained facts only (no forecasts).
Sources & references
- U.S. Naval Observatory — Leap year rules (Gregorian)
- NIST — Why leap years exist; year length context
- timeanddate.com — Next Leap Day (Feb 29, 2028) and Leap Day background
- timeanddate.com — Leap Day dates list; customs terminology (“leaplings”)
- HISTORY — Leap Day odds and widely cited Feb 29 birth estimates
- Condé Nast Traveler — Leap Day proposal tradition (folklore overview)