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What is a Leap year?

A leap year consists of 366 days, as opposed to a common year, which has 365. Nearly every 4 years is a Leap Year, and we add a Leap Day, an extra – or intercalary – day on February 29.

Picture of calendar with Feburary, 29.
Leap years have 29 days in February, not 28.
©bigstockphoto.com/Yulia

Why do we need 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 365.242199 days – or 365 days, 5 hours, 48 minutes, and 46 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 day on February 29 nearly every 4 years, we would lose almost six hours off our calendar every year. After only 100 years, our calendar would be off by approximately 24 days!

Which Years are Leap Years?

In the Gregorian calendar 3 criteria must be taken into account to identify leap years:

  • The year is evenly divisible 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 2000 and 2400 are leap years, while 1800, 1900210022002300 and 2500 are NOT leap years.

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.

Leap Years 2008 – 2032

YearFebruary 29 – day of the week
2008Friday
2012Wednesday
2016Monday
2020Saturday
2024Thursday
2028Tuesday
2032Sunday

Who invented Leap Years?

Julius Caesar introduced Leap Years in the Roman empire over 2000 years ago, but the Julian calendar had only one rule: any year evenly divisible by 4 would be a leap year. This led to way too many leap years, but didn't get corrected until the introduction of the Gregorian Calendar more than 1500 years later.

In this Article

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Leap Year Library

  1. Leap Year in Other Calendars
  2. Bahá'í leap year
  3. Chinese Leap Year
  4. Ethiopian leap year
  5. The Hindu leap year
  6. The Iranian leap year
  7. The Islamic leap year
  8. The Jewish Leap Year
  9. US Election & Olympic games

What and when is Leap Year?



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