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What Is a Leap Year?

Nearly every four years is a leap year which has 366 days, as opposed to a common year, which has 365.

Illustration image

Leap years have 366 days, not 365.

A leap year has 366 days, as opposed to a common year, which has 365 days.

When Is the Next Leap Year?

Next leap day is February 29, 2016.

Last leap day was February 29, 2012.

Why Add Leap Years?

Leap years are needed to keep our modern day Gregorian calendar in alignment with the Earth's revolutions around the sun.

It takes the Earth approximately 365.242189 days – or 365 days, 5 hours, 48 minutes, and 45 seconds – to circle once around the Sun. This is called a tropical year.

However, the Gregorian calendar has only 365 days in a year, so if we didn't add a leap day on February 29 nearly every four years, we would lose almost six hours off our calendar every year. After only 100 years, our calendar would be off by around 24 days!

Is There a Perfect Calendar?

Exactly Which Years Are Leap Years?

We add a Leap Day on February 29, almost every four years. The leap day is an extra, or intercalary, day and we add it to the shortest month of the year, February.

In the Gregorian calendar three criteria must be taken into account to identify leap years:

  • The year can be evenly divided by 4;
  • If the year can be evenly divided by 100, it is NOT a leap year, unless;
  • The year is also evenly divisible by 400. Then it is a leap year.

This means that in the Gregorian calendar, the years 2000 and 2400 are leap years, while 1800, 1900210022002300 and 2500 are NOT leap years.

Special Leap Year 2000

The year 2000 was somewhat special as it was the first instance when the third criterion was used in most parts of the world since the transition from the Julian to the Gregorian Calendar.

Read More About Calendars

Ancient Roman General Julius Caesar
Roman general Julius Caesar.
Roman general Julius Caesar invented leap years.

Who Invented Leap Years?

Roman general Julius Caesar introduced the first leap years over 2000 years ago. But the Julian calendar had only one rule: any year evenly divisible by four would be a leap year.

This formula produced way too many leap years, but was not corrected until the introduction of the Gregorian calendar more than 1500 years later.

Leap Months

The ancient Roman Calendar added an extra month every few years to maintain the correct seasonal changes, similar to the Chinese leap month.

What Is a Leap Second?

Topics: Calendar, Leap Year, February

Leap Days 2016 – 2032

YearFebruary 29 – Day of the Week


Leap Day Library

  1. Leap Day is February 29
  2. Customs & Traditions
  3. Common Year vs. Leap Year
  4. Born on Leap Day
  5. February 30 Was a Real Date

What is a Leap Year?

Alternative Leap Years

  1. Bahá'í Leap Year
  2. Chinese Leap Year
  3. Ethiopian leap year
  4. The Hindu leap year
  5. The Iranian Leap Year
  6. The Islamic leap year
  7. The Jewish Leap Year

Leap Years in Other Calendars

Calendar Types

  1. The Gregorian Calendar
  2. The Julian Calendar
  3. The Revised Julian Calendar
  4. The Mayan Calendar
  5. The Chinese Calendar
  6. The Roman Calendar
  7. Switch from Julian to Gregorian
  8. Is There a Perfect Calendar?

Calendars Library

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The Chinese Calendar

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Ethiopian leap year

A leap year occurs once every 4 years in the Ethiopian calendar, in which 1 extra day is added at the end of the year. more

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The Islamic leap year

A leap year in the the Islamic Hijri calendar occurs 11 times in a 30-year cycle, in which 1 day is added to the last month of the year. more

Lotus Temple, Bahai house of worship in New Delhi, India.

Bahá'í Leap Year

The Bahá'í leap year occurs when 5 intercalary days are added between the last two months of the calendar. Non-leap years in the Bahá'í calendar have 4 intercalary days known as Ayyám-i-Há. Leap years usually occur every 4 years. more