Leap years almost always occur every four years, (i.e. in years that are divisible by 4). The only exceptions to this is that years that are evenly divisible by 100 are not leap years, unless they are also divisible by 400.

So this means that the years 1700, 1800, 1900, etc., were not leap years, but the year 2000 was, and the years 2400 and 2800 will be.

en.wikipedia.org/wiki/Leap_year

A leap year is a calendar year containing one additional day added to keep the
calendar year ..... The observed and calculated versions of the Islamic calendar
do not have regular leap days, even th...

stackoverflow.com/questions/725098/leap-year-calculation

In order to find leap years, why must the year be indivisible by 100 and ... The
length of a year is (more or less) 365.242196 days. So we have to ...

support.microsoft.com/en-us/kb/214019

Dec 17, 2015 ... Describes how to determine whether the year in a date that is used in an Excel
document is a leap year.

www.wikihow.com/Calculate-Leap-Years

How to Calculate Leap Years. To calculate if a year is a leap year is easy. Start
off using the year you want to calculate.

www.mathsisfun.com/leap-years.html

A Leap Year has 366 days (the extra day is the 29th of February). ... Leap Years
are any year that can be evenly divided by 4 (such as 2012, 2016, etc). not ...

www.timeanddate.com/date/leapyear.html

Feb 29, 2016 ... Is 2016 a leap year? A leap year has 366 days, as opposed to a common year,
which has 365. We add a leap day – February 29 – nearly every ...

www.onlineconversion.com/leapyear.htm

Easily determine if a year is a leapyear or not. ... Leap Years Within A Range:
Start Year: End year: Did you find us useful? Please consider supporting the site
...

www.grc.nasa.gov/www/k-12/Numbers/Math/Mathematical_Thinking/calendar_calculations.htm

Our calendar year is shorter than the tropical year by 0.2422 days. So to correct (
approximately), we add 1 day every four years (leap year). Thus, three calendar ...

www.infoplease.com/spot/leapyear2.html

Learn what leap year is, when it is and why we need it. ... Leap Year 101 – Next,
When, List, Days, Calendar, Years, Calculation, Last, Rules ...