非常简单：

    <?php
        $date1 = date_create("2007-03-24");
        echo "Start date: ".$date1->format("Y-m-d")."<br>";
        $date2 = date_create("2009-06-26");
        echo "End date: ".$date2->format("Y-m-d")."<br>";
        $diff = date_diff($date1,$date2);
        echo "Difference between start date and end date: ".$diff->format("%y years, %m months and %d days")."<br>";
    ?>

有关详细信息，请查看以下链接：

PHP:date_diff-手动

注意，它适用于PHP 5.3.0或更高版本。

// If you just want to see the year difference then use this function.
// Using the logic I've created you may also create month and day difference
// which I did not provide here so you may have the efforts to use your brain.
// :)
$date1='2009-01-01';
$date2='2010-01-01';
echo getYearDifference ($date1,$date2);
function getYearDifference($date1=strtotime($date1),$date2=strtotime($date2)){
    $year = 0;
    while($date2 > $date1 = strtotime('+1 year', $date1)){
        ++$year;
    }
    return $year;
}

我建议使用DateTime和DateInterval对象。

$date1 = new DateTime("2007-03-24");
$date2 = new DateTime("2009-06-26");
$interval = $date1->diff($date2);
echo "difference " . $interval->y . " years, " . $interval->m." months, ".$interval->d." days "; 

// shows the total amount of days (not divided into years, months and days like above)
echo "difference " . $interval->days . " days ";

阅读更多php DateTime:：diff手册

根据手册：

从PHP 5.2.2开始，DateTime对象可以使用比较运算符进行比较。

$date1 = new DateTime("now");
$date2 = new DateTime("tomorrow");

var_dump($date1 == $date2); // bool(false)
var_dump($date1 < $date2);  // bool(true)
var_dump($date1 > $date2);  // bool(false)

“如果”日期存储在MySQL中，我发现在数据库级别进行差异计算更容易。。。然后根据“天”、“小时”、“分钟”、“秒”输出，分析并显示相应的结果。。。

mysql> select firstName, convert_tz(loginDate, '+00:00', '-04:00') as loginDate, TIMESTAMPDIFF(DAY, loginDate, now()) as 'Day', TIMESTAMPDIFF(HOUR, loginDate, now())+4 as 'Hour', TIMESTAMPDIFF(MINUTE, loginDate, now())+(60*4) as 'Min', TIMESTAMPDIFF(SECOND, loginDate, now())+(60*60*4) as 'Sec' from User_ where userId != '10158' AND userId != '10198' group by emailAddress order by loginDate desc;
 +-----------+---------------------+------+------+------+--------+
 | firstName | loginDate           | Day  | Hour | Min  | Sec    |
 +-----------+---------------------+------+------+------+--------+
 | Peter     | 2014-03-30 18:54:40 |    0 |    4 |  244 |  14644 |
 | Keith     | 2014-03-30 18:54:11 |    0 |    4 |  244 |  14673 |
 | Andres    | 2014-03-28 09:20:10 |    2 |   61 | 3698 | 221914 |
 | Nadeem    | 2014-03-26 09:33:43 |    4 |  109 | 6565 | 393901 |
 +-----------+---------------------+------+------+------+--------+
 4 rows in set (0.00 sec)

查看以下链接。这是迄今为止我找到的最好的答案

function dateDiff ($d1, $d2) {

    // Return the number of days between the two dates:    
    return round(abs(strtotime($d1) - strtotime($d2))/86400);

} // end function dateDiff

当你通过日期参数。函数使用PHP ABS（）绝对值始终返回正数作为两者之间的天数日期。请记住，两个日期之间的天数不是包括两个日期。因此，如果您正在寻找天数由输入日期之间的所有日期表示，您需要向该函数的结果添加一（1）。例如，差异（由上述函数返回）2013-02-09和2013-02-14之间的值为5。但天数或日期范围2013-02-09-2013-02-14表示的日期为6。

http://www.bizinfosys.com/php/date-difference.html

简单的功能

function time_difference($time_1, $time_2, $limit = null)
{

    $val_1 = new DateTime($time_1);
    $val_2 = new DateTime($time_2);

    $interval = $val_1->diff($val_2);

    $output = array(
        "year" => $interval->y,
        "month" => $interval->m,
        "day" => $interval->d,
        "hour" => $interval->h,
        "minute" => $interval->i,
        "second" => $interval->s
    );

    $return = "";
    foreach ($output AS $key => $value) {

        if ($value == 1)
            $return .= $value . " " . $key . " ";
        elseif ($value >= 1)
            $return .= $value . " " . $key . "s ";

        if ($key == $limit)
            return trim($return);
    }
    return trim($return);
}

像这样使用

回波时间差（$time_1，$time_2，“天”）；

将返回2年8个月2天