Why Do We Have Leap Years and When Is the Next One?

Have you ever met someone with a birthday on February 29th?  These special birthdays only come around every four years, thanks to something called a leap year. But why do we have leap years in the first place?

Leap years, with their extra day every four years, might seem like a quirk, but they play a vital role in ensuring our calendars stay aligned with the Earth’s journey around the Sun.

Why Do We Have Leap Years?

A. The Earth’s Orbit and the Solar Year

Our calendars are based on the cycle of seasons – spring, summer, fall, and winter. This cycle, known as the solar year, is slightly longer than a typical year of 365 days. Here’s why:

  • Sidereal Year vs. Solar Year: The Earth takes a bit longer than 365 days to complete one full orbit around the Sun. This actual orbital period is called a sidereal year and is roughly 365 days, 5 hours, 48 minutes, and 46 seconds.
  • The Missing Pieces: Since calendars can’t have leftover hours, we round down the sidereal year to 365 days. Those extra hours add up over time, causing our calendar to slowly drift out of sync with the seasons.

B. Keeping the Calendar in Sync with Seasons

This is where leap years come in. By adding an extra day every four years, we essentially “catch up” on those missing hours and keep our calendar aligned with the solar year. This ensures that:

  • Seasons Stay Predictable: Farmers rely on the predictability of seasons for planting and harvesting. Leap years ensure the calendar stays synchronized with the Sun’s position relative to Earth, thus maintaining predictability. This ensures spring arrives roughly around the same time each year, allowing farmers to plan their crops accordingly.
  • Holidays Stay Seasonal: Many holidays, like Christmas and Thanksgiving, are tied to specific seasons. For example, Christmas celebrations align with the winter solstice in the Northern Hemisphere. Leap years prevent these holidays from gradually drifting into different seasons over time. Imagine celebrating Christmas in July! Leap years ensure these traditions remain connected to their intended seasons.

History of Leap Years

The concept of leap years has been around for centuries, with different civilizations developing their own methods to account for the Earth’s orbital discrepancy:

  • The Julian Calendar: Introduced by Julius Caesar in 45 BC, the Julian calendar added an extra day every three years. This system was a significant improvement over previous lunar calendars but wasn’t perfect. The extra day every three years was slightly too much, causing the calendar to drift out of sync with the solar year over time.
  • The Gregorian Calendar: The current system, implemented in 1582 by Pope Gregory XIII, addressed the shortcomings of the Julian calendar. It adds an extra day every four years with some exceptions (we’ll get to those later). This system provides a more accurate way to account for the Earth’s orbit and keeps our calendar in better alignment with the solar year.

Fun Facts about Leap Years

Leap years come with some interesting trivia that add a touch of lightheartedness to the calendar:

  • The Odds of a February 29th Birthday: The chance of being born on February 29th is about 1 in 1,461! That makes it a pretty exclusive birthday to have.
  • Leap Year Traditions: Leap years have inspired unique traditions around the world. In Greece, it’s considered bad luck for women to propose on a leap year. Perhaps this stems from the idea of women having an “extra day” to take initiative in a leap year. In Ireland, there’s a tradition of women proposing to men on February 29th, turning the tables on the usual proposal dynamic.
  • Double Trouble: Very rarely, February 29th can coincide with a day of the week twice in a leap year. This last happened in 2016 (a leap year that was also a Monday) and won’t occur again until 2424! Imagine having two Mondays on the same date – a truly unique leap year phenomenon.

When is the Next Leap Year?

The next leap year will be in 2028. But how can you determine future leap years? Here’s a simplified rule of thumb:

  • Generally Leap Year Every Four Years: A year is usually considered a leap year if it’s divisible by 4. This is because four years is roughly how long it takes to accumulate those extra “missing hours” from the Earth’s orbit.

There are some exceptions to this rule, though:

  • Century Years (Not Always): Years ending in “00” (centuries) are not leap years unless they are also divisible by 400. For example
  • 1900 was not a leap year as it is not divisible by 400.
  • 2000 was a leap year as it is divisible by 400.
  • 2100 will not be a leap year (not divisible by 400).

These exceptions further refine the leap year system, ensuring even greater accuracy in keeping our calendar aligned with the solar year over extended periods.


Leap years, with their extra day every four years, might seem like a calendar oddity. But they play a crucial role in maintaining harmony between our timekeeping system and the Earth’s movement around the Sun. 

Leap years ensure the predictability of seasons for agriculture, prevent holidays from drifting into different seasons, and add a touch of uniqueness to the calendar, with special birthdays and interesting traditions around the world. 

So, the next time you encounter February 29th or hear about a leap year, remember the clever way our calendar system accounts for the Earth’s journey and keeps us in sync with the rhythm of the seasons.


1. Is the Next Leap Year the Same Worldwide?

Yes, the concept of a leap year and the extra day in February apply almost universally around the world.

2. Are there any traditions or superstitions around leap years?

Yes! Leap years have inspired unique traditions worldwide. In some cultures, it’s considered bad luck for women to propose on a leap year, while others have traditions where women propose to men on February 29th.

3. Can February 29th fall on the same day of the week twice in a leap year?

Very rarely, yes! This phenomenon, where February 29th shares the same day of the week twice in a leap year, last happened in 2016 and won’t occur again until 2424.