function get_daydiff($end_date,$today)
{
    if($today=='')
    {
        $today=date('Y-m-d');
    }
    $str = floor(strtotime($end_date)/(60*60*24)) - floor(strtotime($today)/(60*60*24));
    return $str;
}
$d1 = "2018-12-31";
$d2 = "2018-06-06";
echo get_daydiff($d1, $d2);

如果你使用的是PHP 5.3 >，这是目前为止最准确的计算绝对差值的方法:

$earlier = new DateTime("2010-07-06");
$later = new DateTime("2010-07-09");

$abs_diff = $later->diff($earlier)->format("%a"); //3

如果你需要一个相对的(带符号的)天数，可以用这个代替:

$earlier = new DateTime("2010-07-06");
$later = new DateTime("2010-07-09");

$pos_diff = $earlier->diff($later)->format("%r%a"); //3
$neg_diff = $later->diff($earlier)->format("%r%a"); //-3

更多关于php的DateInterval格式可以在这里找到:https://www.php.net/manual/en/dateinterval.format.php

$now = time(); // or your date as well
$your_date = strtotime("2010-01-31");
$datediff = $now - $your_date;

echo round($datediff / (60 * 60 * 24));

$diff = strtotime('2019-11-25') - strtotime('2019-11-10');
echo abs(round($diff / 86400));

这是我的改进版本，显示1年2月25天(s)，如果通过第二个参数。

class App_Sandbox_String_Util {
    /**
     * Usage: App_Sandbox_String_Util::getDateDiff();
     * @param int $your_date timestamp
     * @param bool $hr human readable. e.g. 1 year(s) 2 day(s)
     * @see http://stackoverflow.com/questions/2040560/finding-the-number-of-days-between-two-dates
     * @see http://qSandbox.com
     */
    static public function getDateDiff($your_date, $hr = 0) {
        $now = time(); // or your date as well
        $datediff = $now - $your_date;
        $days = floor( $datediff / ( 3600 * 24 ) );

        $label = '';

        if ($hr) {
            if ($days >= 365) { // over a year
                $years = floor($days / 365);
                $label .= $years . ' Year(s)';
                $days -= 365 * $years;
            }

            if ($days) {
                $months = floor( $days / 30 );
                $label .= ' ' . $months . ' Month(s)';
                $days -= 30 * $months;
            }

            if ($days) {
                $label .= ' ' . $days . ' day(s)';
            }
        } else {
            $label = $days;
        }

        return $label;
    }
}

function howManyDays($startDate,$endDate) {

    $date1  = strtotime($startDate." 0:00:00");
    $date2  = strtotime($endDate." 23:59:59");
    $res    =  (int)(($date2-$date1)/86400);        

return $res;
}