/**
 * Calculates the differences between two date
 * 
 * @param date $date1
 * @param date $date2
 * @return array
 */
function dateDifference($date1, $date2)
{
    $d1 = (is_string($date1) ? strtotime($date1) : $date1);
    $d2 = (is_string($date2) ? strtotime($date2) : $date2);

    $diff_secs = abs($d1 - $d2);
    $base_year = min(date("Y", $d1), date("Y", $d2));

    $diff = mktime(0, 0, $diff_secs, 1, 1, $base_year);

    return array
    (
        "years"                 => abs(substr(date('Ymd', $d1) - date('Ymd', $d2), 0, -4)),
        "months_total"  => (date("Y", $diff) - $base_year) * 12 + date("n", $diff) - 1,
        "months"                => date("n", $diff) - 1,
        "days_total"    => floor($diff_secs / (3600 * 24)),
        "days"                  => date("j", $diff) - 1,
        "hours_total"   => floor($diff_secs / 3600),
        "hours"                 => date("G", $diff),
        "minutes_total" => floor($diff_secs / 60),
        "minutes"               => (int) date("i", $diff),
        "seconds_total" => $diff_secs,
        "seconds"               => (int) date("s", $diff)
    );
}

http://stackoverflow.com/questions/388673/php-date-calculation

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