What Is a Leap Year?
A leap year is a year with 366 days instead of the usual 365. The extra day — February 29th — is added to keep our calendar aligned with the Earth's orbit around the Sun. ☀️
Why Do We Need Leap Years?
The solar (tropical) year — the time it takes Earth to complete one full orbit — is approximately 365 days, 5 hours, 48 minutes, and 45 seconds. Those extra ~6 hours accumulate over four years to equal roughly one full day. Without leap years, our calendar would drift by about 24 days every century, completely misaligning the seasons.
How to Calculate a Leap Year
A year is a leap year if it meets one of these rules:
- The year is divisible by 4 — e.g., 2024 ÷ 4 = 506 ✅
- Exception: if the year is also divisible by 100, it is not a leap year — e.g., 1700, 1800, 1900 ❌
- Exception to the exception: if the year is divisible by 400, it is a leap year — e.g., 1600, 2000 ✅
In short: (year % 4 == 0 && year % 100 != 0) || (year % 400 == 0)
Interesting Leap Years
- 2024 — The most recent leap year. Paris hosted the Summer Olympics.
- 2020 — A memorable leap year marked by the COVID-19 pandemic. 🦠
- 2012 — Queen Elizabeth II marked the 60th anniversary of her coronation. CERN announced a particle consistent with the Higgs boson.
- 2000 — A special leap year (divisible by 400). The start of the new millennium. The ISS received its first resident crew. 🧬
- 1992 — Space Shuttle Atlantis launched to study global warming. Microsoft released Windows 3.1. 🚀
- 1960 — 17 African countries declared independence. Elvis Presley returned from Germany. New Zealand had its first TV broadcast. 📺
- 1900 — Not a leap year! Divisible by 100 but not by 400.
All Leap Years Since 1900
1904, 1908, 1912, 1916, 1920, 1924, 1928, 1932, 1936, 1940, 1944, 1948, 1952, 1956, 1960, 1964, 1968, 1972, 1976, 1980, 1984, 1988, 1992, 1996, 2000, 2004, 2008, 2012, 2016, 2020, 2024, 2028, 2032…
FAQs
When is the next leap year?
The next leap year after 2024 is 2028. Leap years occur every four years (with the century-rule exceptions).
Is 2100 a leap year?
No. 2100 is divisible by 100 but not by 400, so it is not a leap year. The next century leap year will be 2400.
What happens to people born on February 29?
People born on February 29 (sometimes called leaplings or leap-day babies) celebrate their "official" birthday only once every four years! In non-leap years they typically celebrate on either February 28 or March 1, depending on local custom or personal preference.
Does the Gregorian calendar perfectly track the solar year?
Almost — but not perfectly. The Gregorian calendar is off by roughly 26 seconds per year. After about 3,300 years this will amount to a one-day error, but for now the calendar serves us extremely well.
Are there other leap year systems?
Yes! The Hebrew calendar adds a full leap month (13th month) seven times every 19 years. The Islamic (Hijri) calendar also has a leap-day system. The Julian calendar used only the "divisible by 4" rule, which is why it drifted over time and was eventually replaced by the Gregorian calendar in 1582.