The leap year is a device used in all solar calendars to keep them correct. Since each year is made up of 365 days and 6 hours approximately, with the introduction of the leap year, which provides for the addition of one day every 4 years, the difference of 6 hours of the previous years is "corrected". Calculating whether a year is a leap year or not is very simple, but there are some very specific rules to keep in mind. If you don't like math, you can use the calendar to find out when a year will be leap year.
Steps
Method 1 of 2: Use Divisions
Step 1. Find the year you want to check
To check whether a year is a leap year or not, it is necessary to start from the corresponding number. You can use a past year, the current year, or a future year as a starting point.
For example, you can start from 1997 or 2012, if you want to check a year that has already passed, or you can check if the current year, 2019, is a leap year. If you are interested in the future, you can take 2025 or 2028 as a reference
Step 2. Check if the reference year is divisible by 4
Divide the year number by 4 and verify that the remainder is zero. If so, the year under review was, is or will be a leap year. If the remainder is non-zero, it means that the year tested is not a leap year.
- For example, dividing 1997 by 4 yields 499 with the remainder of 1; therefore, since it is not divisible by 4, it cannot be a leap year. If the remainder of the division is zero, it means it is a leap year.
- Dividing 2012 by 4 results in 503, an integer. This means that 2012 was a leap year.
Step 3. Verify that the year under review is not divisible by 100
If the chosen number is divisible by 4, but not by 100, it means it is a leap year. If the year under consideration is divisible both by 4 and by 100, there is a possibility that it is not a leap year and to verify this you will need to make an additional calculation.
- For example, the year 2012 is divisible by 4, but not by 100 (since 2012/100 = 20, 12), so you can be sure that it is a leap year.
- The year 2000 is divisible by both 4 and 100 (since 2000/100 = 20). This means that 2000 may be a leap year, but to be sure you will need to perform one final division.
Step 4. Check if the year in question is a leap year by checking if it is also divisible by 400
If a year is divisible by 4, by 100, but not by 400, it means that it is not a leap year. Conversely, if it is divisible by 4, 100 and 400 it is definitely a leap year.
- For example, 1900 is divisible by 100, but not by 400 (since 1900/400 = 4.75), so it wasn't a leap year.
- Conversely, 2000 is divisible by 4, 100 and 400 (since 2000/400 = 5), so it was definitely a leap year.
advise: If you don't want to do all these calculations by hand or aren't sure what you got, you can use a web service that does the calculations for you.
Method 2 of 2: Check the Calendar
Step 1. Find the year you want to check in an electronic or paper calendar
Start by identifying the year you want to check, then use a paper or electronic calendar to carry out the checks. If you have chosen to use an electronic calendar, you will have the possibility to check more than one year, both past and future.
- For example, if you want to check if 2016 was a leap year, get the relevant paper calendar.
- If you want to know if 2021 will be a leap year, use an electronic calendar.
Step 2. Check if the month of February has 29 days
Leap years are 366 days and not 365; in particular, 1 day is added to the month of February, since it is the shortest of the year. Browse the calendar up to February to check if the 29th day exists; if so, it is a leap year.
If February has only 28 days, it is not a leap year
Step 3. Expect a leap year every 4 years
This happens because by convention the duration of a calendar year has been fixed at 365 days, but in reality each year lasts about 365 days and 6 hours. Over a period of 4 years, the 6 extra hours of each calendar year add up to make up an entire day; for this reason every 4 years there is almost always a leap year consisting of 366 days. After locating a leap year on the calendar, you can assume that the next one will fall 4 years later.
For example, since the last leap year was 2016, you can predict that 2020 will be next, given that 2016 + 4 = 2020
advise: remember that sometimes you have a leap year only after 8 years, instead of 4. This happens because the annual difference is slightly less than 6 hours (in reality it is equal to 5 hours, 48 minutes and 46 seconds). It is for this reason that it is always better to stick to mathematical calculations rather than the rule that every 4 years there is a leap year.
