直接看程式碼就知道啥意思了！

<?php

// 獲取明天凌晨時間戳：
echo "今天凌晨的時間戳:" . strtotime(date("Y-m-d")) . PHP_EOL;

echo "一天後:" . date("Y-m-d", strtotime("+1 day")) . PHP_EOL;

echo "一週後:" . date("Y-m-d", strtotime("+1 week")) . PHP_EOL;

echo "一週零兩天四小時兩秒後:" . date("Y-m-d G:H:s", strtotime("+1 week 2 days 4 hours 2 seconds"
 
)) . PHP_EOL;

echo "下個星期四:" . date("Y-m-d", strtotime("next Thursday")) . PHP_EOL;

echo "上個週一:" . date("Y-m-d", strtotime("last Monday")) . PHP_EOL;

echo "一個月前:" . date("Y-m-d", strtotime("last month")) . PHP_EOL;

echo "一個月後:" . date("Y-m-d", strtotime("+1 month")) . PHP_EOL;

echo "十年後:" . date("Y-m-d"
 
, strtotime("+10 year")) . PHP_EOL;


//如果需要的是時間戳，那就更簡單了：

echo strtotime("now"), "\n";

echo strtotime("+0 day"), "\n";

echo strtotime("10 September 2000"), "\n";

echo strtotime("+1 day"), "\n";

echo strtotime("+1 week"), "\n";

echo strtotime("+1 week 2 days 4 hours 2 seconds"), "\n";

echo strtotime("next Thursday"
 
), "\n";

echo strtotime("last Monday"), "\n";

//昨天
print date('Y-m-d', strtotime('-1 day')) . PHP_EOL;
//上星期
print date('Y-m-d', strtotime('-1 week')) . PHP_EOL;
//上個月
print date('Y-m-d', strtotime('-1 month')) . PHP_EOL;
//去年
print date('Y-m-d', strtotime('-1 year')) . PHP_EOL;

怎麼樣，是不是很有用處！

看看效果：

補充–2018.3.19

#上週一
$data = date('Y-m-d H:i:s', strtotime('-1 monday'));
#下週一
$data = date('Y-m-d H:i:s', strtotime('+2 monday'));

#計算生日
function birthday2($birthday)
{
    list($year, $month, $day) = explode("-", $birthday);
    $year_diff = date("Y") - $year;
    $month_diff = date("m") - $month;
    $day_diff = date("d") - $day;
    if ($day_diff < 0 || $month_diff < 0) {
        $year_diff--;
    }
    return $year_diff;
}