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Checking For Leap Year Using PHP

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One part of programming that seems pretty static is dealing with dates. The calendar is a set system of rules that doesn't look to change. The only part of the calendar that can be variable is a leap year, which changes every four years (obviously).

Using pure PHP ternary logic, much like the PHP Function - Calculating Days In A Month, I posted a few weeks back, you can check to see if a year is a leap year.

The Code

function is_leap_year($year) {
	return ((($year % 4) == 0) && ((($year % 100) != 0) || (($year % 400) == 0)));
}
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Discussion

  1. Keith

    Placing a function call as an argument default will result in a fatal error. Also, give this version a shot:

    function is_leap_year( $year = NULL )
{
    if_numeric( $year ) || $year = date( 'Y' );
    return checkdate( 2, 29, ( int ) $year );
}
  2. Keith

    Whoops, small typo… if_numeric( $year ) should be is_numeric( $year )… :x

  3. Tamlyn

    Better yet, use date('L') which returns 1 if it’s a leap year, 0 if it isn’t.

  4. Jasa Web Desain

    I do agree with tamlyn, why you dont use date function??
    It can makes a load fasting right?

  5. Travis

    date(‘L’) is way better because leap year is not every 4 years.

  6. Indra

    Date("L") only tell you in a given year, default is the year today.
    If you need to know whether previous or next year is a leap, you must reset the date.
    It could affect the system.

    • Lossy

      Indra, you can always pass the timestamp as second parameter to date function:

      echo date('L', mktime(1, 1, 1, 1, 1, 2005));
  7. iCalculator

    I think this is a better example relating to the function. Also provided example for anyone looking for true/false as I was in this instance.

    /* for true or false */
function is_leap_year($year)
{
	return ( date ('L', mktime(1,1,1,1,1, $year) ) === 1 ) ? true : false;
}
/*for 0 or 1 Whether it's a leap year: 1 if it is a leap year, 0 otherwise. */
function is_leap_year($year)
{
	return date ('L', mktime(1,1,1,1,1, $year) );		
}
  8. Habibur Rahaman
    <?php
$day = "";
for($i=0; $i<4; $i++)
{
    $day =  date("d", mktime(0, 0, 0, 2, 29, date("Y")+$i));
    if($day == 29)
    {
        $year = date("Y")+$i;
        break;
    }
}
echo "The next leap year is 29th February $year";    
?>
  9. Milan Dvořák

    code of Habibur Rahaman will not work for example for the year 1897, because 1900 is not leap year.

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