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Why do we have leap years and when was the last one?

It is rare to be born on a leap day (Alamy / PA)
It is rare to be born on a leap day (Alamy / PA)

As we reach the last week of February, there may be many people wondering why we have an extra day at the end of the month.

In some places around the world, leap years are considered lucky while, elsewhere, a February 29 birthday is thought to be unfortunate.

But, one thing is for certain: Without leap years, there would be nothing to keep our months and years in check.

So what is a leap year and when is the next one?

What is a leap year?

Most of the world uses the Gregorian calendar. It has 365 days a year, plus one additional day every four years. These years are called leap years.

The Roman general Julius Caesar instituted leap years in the Western calendar more than 2,000 years ago. The Julian calendar, which bears his name, had just one rule: a leap year was declared in any year that could be divided evenly by four.

However, this formula wasn’t exact enough and wasn’t corrected until the introduction of the Gregorian calendar more than 1,500 years later, when some days were skipped to realign our calendar with the seasons.

In a leap year, the shortest month, February, gets an extra day at the end of it. This so-called intercalary day, February 29, is commonly referred to as leap day.

Leap years have 366 days instead of the usual 365 days and occur almost every four years.

When is the next leap year?

February 29, 2024 is a leap day. The last leap day was February 29, 2020, and the next one is February 29, 2028.

Why does leap year exist?

Our calendar remains in sync with Earth's rotations around the Sun thanks to leap days. Earth completes one orbit of the Sun in about 365.242189 days, or 365 days, five hours, 48 minutes, and 45 seconds. The equinox in March marks the beginning of what is known as a tropical year.

Only 365 days make up a year on the Gregorian calendar. In regard to Earth's rotation around the Sun, each calendar year would start around six hours earlier if we didn't add a leap day on February 29 almost every four years.

How do leap year birthdays work?

Being born on February 29 is quite rare: the Office for National Statistics (ONS) reports that February 29 technically has the lowest number of births between 1995 and 2014.

However, it's not the rarest birthday, on average. The ONS reports that 1,788 people are born on February 29, on average, compared to 1,422 on Christmas Day and 1,359 on Boxing Day,

Although people born on a leap day will only get to mark their actual birthdate every four years, they will typically celebrate turning a year older on either February 28 or March 1 on non-leap years.

But people born on February 29 may choose to have an extra special celebration every four years.

Are leap years lucky?

Leap years are considered to be lucky in some cultures.

For example, it is a tradition for women to pop the question to men on the extra day.

According to Irish legend, St Patrick issued his proclamation allowing women to pop the question to men on the additional day of a leap year, after being informed by St Brigid of Kildare that maidens were forced to wait too long for their suitors to ask for their hands in marriage.

However, leap years are considered unlucky by some. For instance, Greek people are said to believe that couples who get married during a leap year will get divorced, while some people believe that it's unfortunate to be born on February 29.