To calculate if a year is a leap year is easy.
1Start off using the year you want to calculate.
2See if it is evenly divisible by 4 (a whole number with no remainder). If it is not, like 1997, it is not a leap year. If it is, like 2012, keep reading.
3See if the year is divisible by 100. If a year is divisible by 4, but not 100, like 2012, it is a leap year. If a year is divisible by both 4 and 100, like 2000, keep reading.
4See if the year is divisible by 400. If a year is divisible by 100, but not 400, like 1900, then it is not a leap year. If a year is divisible by both, then it is a leap year. So 2000 was indeed a leap year.
Why do we check for divisibility by 100? Is it not enough to check divisibility by 4?wikiHow ContributorNo, there is still a small error that must be accounted for. To eliminate this error, the Gregorian calendar stipulates that a year that is evenly divisible by 100 (for example, 1900) is a leap year only if it is also evenly divisible by 400. For this reason, the following years are not leap years: 1700, 1800, 1900, 2100, 2200, 2300, 2500, 2600. This is because they are evenly divisible by 100 but not by 400.
Since you state "any year divisible by 4 is a leap year," why aren't 1700, 1900 and 2100 leap years?wikiHow ContributorBecause, just as a 365-calendar undershoots measuring our trip around the sun (by about .25 days every year, to be more precise), over time, adding a whole day every 4 years overshoots it a tiny bit as well. This is why we add a day every 4 years, but we pull it back a bit around every 100 years. It's all meant to find the most easily calculated plan to measure our days according to the solar system.
Why do we have leap years?wikiHow ContributorEach year is technically 12 months and a fraction of a day, close to .25. Every four years, the fraction is compiled to create a whole day and added to that year.
- Leap years: 1600, 1604, 1608, 1612, 1616...1684, 1688, 1692, 1696, 1704 (no 1700, see why?), 1708, 1712...1792, 1796, 1804 (no 1800), 1808, 1812...1892, 1896, 1904 (no 1900), 1908, 1912...1992, 1996, 2000 (there is a 2000, see why?), 2004, 2008, 2012...2092, 2096, 2104 (no 2100)...2196, 2204...2296, 2304...2396, 2400 (see why?), 2404...etc.
- Any year divisible by "4" is a leap year. 1 year is ‘365 days + 6 hours', which is the same as 365 and 1/4 days. Every 4 years, the 6 hours become one day (6X4=24 hours) and the reason why we have extra day in February.
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