How to Identify a Leap Year in Simple Steps
It takes approximately 365.25 days for our planet Earth to orbit the Sun — that is a solar year. We usually round the days in a calendar year to 365, that is 365 days in a year. To make up for the missing partial day, we add one day to our calendar approximately every four years and that is known as a leap year.
In an ordinary year, if you were to count all the days in a calendar from January to December, you’d count it as 365 days. But approximately every four years, the month of February has 29 days instead of 28. So, there are 366 days in the year. This is called a leap year.
Why Do We Have Leap Years?
A year can be defined as the amount of time it takes any planet to orbit its star one time. A day can be defined as the amount of time it takes a planet to finish one rotation on its axis.
It takes our planet Earth approximately 365 days and 6 hours to orbit the Sun, that is, it takes Earth approximately 24 hours — 1 day — to rotate on its axis. So, our one year is not an exact number of days.
Because of that, we round the days in a year down to 365 for most years. However, that one day doesn’t disappear. To make sure that we count that extra part of a day, we add one day to the calendar every four years. Here’s a table that shows how it works:
Because we’ve subtracted approximately six hours — or we can say that ¼ of a day — from 2017, 2018, and the year 2019, we have to make up that time in 2020 and that’s why we have a leap day!
Evaluation of Leap Year
The leap year occurs every 4 years, but there are scenarios where the gap between two leap years was 8 years instead of the regular 4 years.
Example: The year 1896 is a leap year. The next leap year comes in 1904 (The year 1900 is not a leap year).
In order to make the investigation easier, any year which is divisible by the number 4 completely (that is the remainder becomes zero) is considered as a leap year.
Example: 1888, 2012, 2016 are known to be leap years as it’s completely divisible by 4. Years like 2009, 2019, etc. are not divisible by 4 completely, therefore, they are normal years.
An Exception to Note:
A year 700 is completely divisible by 4, but this year is not considered as a leap year. For a century, the logic follows that any year should always be divisible by 400 not by 4. Even though the year 700 is divisible by 4 but not by the number 400. Hence, we cannot consider the year 700 as a leap year.
Example: 400, 800, 1200, etc. are leap years as they are divisible by 400, and years 300, 700, 100, etc are not leap years as these years are not divisible by 400.
Why?
We have discussed above, we know that because the Earth rotates about 365.242375 times a year but a normal year is 365 days, something has to be done to "catch up" the extra 0.242375 days a year.
So every fourth year we add an extra day (the 29th of February), which makes 365.25 days a year. This is fairly close but is wrong by about 1 day every 100 years.
So every 100 years we don't have a leap year, and that gets us 365.24 days per year (1 day less in 100 years = -0.01 days per year). Closer, but still not accurate enough!
So another rule says that every 400 years is a leap year again, this gets us 365.2425 days per year (that is 1 day regained every 400 years equals 0.0025 days per year), which is close to 365.242375 not to matter much.
How to Determine Whether Any Year is a Leap Year?
To determine whether any given year is a leap year, follow these steps:
If the year is evenly divisible by four, then go to step 2. Otherwise, go to step 5.
If the year is evenly divisible by a hundred, then go to step 3. Otherwise, go to step 4.
If the year is evenly divisible by four hundred, then go to step 4. Otherwise, you can go to step 5.
The year is a leap year (if it has 366 days).
The year is not a leap year (if it has 365 days).
FAQs on Leap Year: Meaning, Rules & Examples
1. What is the definition of a leap year in Maths?
A leap year is a calendar year that contains an additional day compared to a common year. This extra day is added to keep the calendar year synchronised with the astronomical or seasonal year. A leap year has 366 days instead of the usual 365 days. The extra day is added to February, making it 29 days long.
2. What are the rules to determine if a year is a leap year?
To determine if a year is a leap year, you can follow these two main rules as per the Gregorian calendar system taught in the CBSE syllabus:
- A year must be evenly divisible by 4. For example, 2024 is divisible by 4, so it is a leap year.
- However, if the year is a century year (divisible by 100), it must also be divisible by 400 to be a leap year. For instance, 1900 was not a leap year, but 2000 was.
3. Why is an extra day added to the calendar every four years?
An extra day is added because the Earth's orbit around the sun takes approximately 365.24 days, not exactly 365 days. This extra 0.24 of a day accumulates over time. By adding one full day (February 29th) nearly every four years, our calendar stays aligned with the Earth's journey around the sun and prevents the seasons from drifting over centuries.
4. Is the year 2025 a leap year? Explain with the calculation.
No, the year 2025 is not a leap year. To check, we apply the first rule of calculation: divide the year by 4. The number 2025 is not evenly divisible by 4 (2025 ÷ 4 = 506.25). Since it fails this basic test, it is a common year with 365 days. The most recent leap year was 2024, and the next one will be 2028.
5. What is the importance of the century rule for leap years? For example, why was 1900 not a leap year?
The century rule provides a crucial correction to the calendar. Simply adding a day every four years would slightly overcorrect for the 365.24-day orbit. The century rule states that a year divisible by 100 is not a leap year unless it is also divisible by 400. This is why 1900 was not a leap year (divisible by 100 but not by 400), but the year 2000 was a leap year (divisible by both 100 and 400). This adjustment makes the calendar system extremely accurate over long periods.
6. What would be the real-world consequence of not having leap years?
If we stopped observing leap years, our calendar would slowly fall out of sync with the Earth's seasons. Every four years, the calendar would be off by about one day. After just 100 years, it would be off by approximately 24 days. This means that significant events like the summer solstice would no longer occur around June 21st but would drift into July, disrupting agriculture, seasonal planning, and traditional festivities tied to specific times of the year.
7. How many leap years are there between 2001 and 2025?
To find the number of leap years between 2001 and 2025, we list the years in this range that are divisible by 4. These years are: 2004, 2008, 2012, 2016, 2020, and 2024. None of these are century years, so we don't need to apply the second rule. Therefore, there are a total of six leap years between 2001 and 2025.
8. What is a common way for people born on February 29th to celebrate their birthday?
People born on February 29th, sometimes called "leaplings" or "leapers," get to celebrate on their actual birth date only once every four years. In common years (non-leap years), they typically choose to celebrate their birthday on either February 28th or March 1st. The choice is a personal preference, and both days are common for celebrations.
