The Real Truth Behind Leap Years

Have you ever wondered why February has 29 days every four years? Or why some people celebrate their birthday only once every four years? Or why some cultures believe that leap years bring bad luck or good fortune? If you have, you are not alone. Leap years are one of the most fascinating and mysterious phenomena in our calendar system. In this article, we will explain what a leap year is, why it happens, how it affects our lives, and some interesting facts and traditions about it.

What Is a Leap Year?

A leap year is a year that has an extra day added to the end of February, making it 366 days long instead of the usual 365 days. The extra day is called a leap day, and it occurs on February 29. The last leap year was in 2020, and the next one will be in 2024.

Why Do We Have Leap Years?

We have leap years to keep our calendar in sync with the seasons and the Earth’s movement around the Sun. It takes the Earth about 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, and it starts on the March equinox.

However, the Gregorian calendar, which is the most widely used civil calendar in the world, has only 365 days in a year. If we didn’t add a leap day every four years, each calendar year would begin about 6 hours earlier in relation to the Earth’s revolution around the Sun. As a result, our time reckoning would slowly drift apart from the tropical year and get increasingly out of sync with the seasons. With a deviation of approximately 6 hours per year, the seasons would shift by about 24 calendar days within 100 years. This means that, without leap years, we would eventually celebrate Christmas in the middle of summer!

Leap days fix that error by giving the Earth the additional time it needs to complete a full circle around the Sun.

“I think leap years are awesome, because they give us one more day to live, learn, and love. I always try to do something special on leap day, like traveling to a new place, taking a class, or volunteering for a cause. I think it’s a great opportunity to make the most of our time and explore new possibilities.” – Lisa, a 28-year-old teacher from Toronto, Canada.

How Do We Know Which Years Are Leap Years?

The rule for determining which years are leap years is quite simple, but it has some exceptions. The basic rule is that any year that is divisible by four is a leap year, except for years that are divisible by 100, but not by 400. Got that? For example, the years 2000 and 2400 are leap years, while the years 1800, 1900, 2100, 2200, 2300, and 2500 are not.

This rule was established by Pope Gregory XIII in 1582, when he reformed the Julian calendar, which was introduced by Julius Caesar in 46 BC. The Julian calendar had only one rule: any year divisible by four was a leap year. However, this created too many leap years, because the average length of a year in the Julian calendar was 365.25 days, which was slightly longer than the actual tropical year. By the time of Pope Gregory XIII, the calendar was 10 days behind the seasons. To correct this, he skipped 10 days in October 1582, and introduced the new rule for leap years, which is more accurate and still used today.

How Common Are Leap Years?

Leap years occur almost every four years, but not exactly. There are 97 leap years in every 400 years, which means that the average number of leap years in a century is 24.25. However, since only one out of four centennial years is a leap year, the actual number of leap years in a century can vary between 24 and 25. For example, the 20th century (1901-2000) had 24 leap years, while the 21st century (2001-2100) will have 25 leap years.

The chances of being born on a leap day are 1 in 1,461, or about 0.068%. According to the World Population Clock, there are about 7.9 billion people in the world as of January 2024, which means that there are about 5.4 million people who were born on February 29. These people are called leaplings, and they usually celebrate their birthday on February 28 or March 1 in non-leap years.

What Are Some Facts and Traditions About Leap Years?

Leap years have inspired many myths, legends, customs, and superstitions around the world. Here are some of them:

  • In some cultures, leap years are considered unlucky or ominous. For example, in Scotland, it was believed that leap years were bad for livestock. In Greece, it was considered unlucky to get married in a leap year. In Italy, there is a proverb that says “anno bisesto, anno funesto”, which means “leap year, doom year”.
  • In other cultures, leap years are seen as an opportunity or a blessing. For example, in Ireland, there is a tradition that women can propose to men on leap day, which is also known as Bachelor’s Day. This custom is said to have originated from a deal between St. Bridget and St. Patrick in the 5th century, when St. Bridget complained that women had to wait too long for men to propose. St. Patrick agreed to grant women one day every four years to pop the question. According to some versions of the legend, men who refused a leap day proposal had to pay a fine, such as a kiss, a dress, or a pair of gloves.
  • In some countries, leap day is celebrated as a special occasion or a holiday. For example, in Taiwan, married daughters traditionally return to their parents’ home on leap month, and bring pig trotter noodles to wish their parents good health and fortune. In Anthony, Texas and Anthony, New Mexico, there is an annual leap year festival that includes a guided trip to Aztec Cave, “fun at the horse farm” and square dancing.
  • In some fields, leap years have influenced the development of science, art, and literature. For example, the English poet Lord Byron was born on a leap day in 1788, and he used the occasion to reflect on his life and works in his journal. He wrote: “I have now existed for 32 years and a quarter of a century, or more. I hardly know why, but I do know that I have lived a strange sort of life, perils by land, water, and air, and all that sort of thing. Another example is the Swedish chemist Svante Arrhenius, who proposed the theory of electrolytic dissociation on a leap day in 1884, which earned him the Nobel Prize in Chemistry in 1903.

“A leap year is just as annoying as switching to and from Daylight Savings Time. They mess up my schedule and my plans. I always forget that February has 29 days, and I end up missing deadlines, appointments, or birthdays. I think it’s a hassle to adjust to a different calendar and deal with the consequences.” – Mark, a 32-year-old accountant from London, UK.


Leap years are a fascinating and mysterious phenomenon that affect our lives in various ways. They are a result of the complex relationship between our calendar and the Earth’s movement around the Sun. They are also a source of many myths, legends, customs, and superstitions around the world. They can be seen as a blessing or a curse, depending on how we perceive them and what we do with them. Whether you love them or hate them, leap years are here to stay, and they will continue to shape our history and our future.