选择的答案不是最正确的答案，因为它将在UTC之外失败。 根据时区(列表)，可能会有时间调整创建“没有”24小时的日子，这将使计算(60*60*24)失败。

这里有一个例子:

date_default_timezone_set('europe/lisbon');
$time1 = strtotime('2016-03-27');
$time2 = strtotime('2016-03-29');
echo floor( ($time2-$time1) /(60*60*24));
 ^-- the output will be **1**

因此，正确的解决方案是使用DateTime

date_default_timezone_set('europe/lisbon');
$date1 = new DateTime("2016-03-27");
$date2 = new DateTime("2016-03-29");

echo $date2->diff($date1)->format("%a");
 ^-- the output will be **2**

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

PHP中两个日期之间的天数

      function dateDiff($date1, $date2)  //days find function
        { 
            $diff = strtotime($date2) - strtotime($date1); 
            return abs(round($diff / 86400)); 
        } 
       //start day
       $date1 = "11-10-2018";        
       // end day
       $date2 = "31-10-2018";    
       // call the days find fun store to variable 
       $dateDiff = dateDiff($date1, $date2); 

       echo "Difference between two dates: ". $dateDiff . " Days "; 

$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));

你可以试试下面的代码:

$dt1 = strtotime("2019-12-12"); //Enter your first date
$dt2 = strtotime("12-12-2020"); //Enter your second date
echo abs(($dt1 - $dt2) / (60 * 60 * 24));