2行代码，你就完成了:

$oDate = new DateTime("2019-11-23");

// now your date object has been updated with last day of month    
$oDate->setDate($oDate->format("Y"),$oDate->format("m"),$oDate->format("t"));

// or to just echo you can skip the above line using this
echo $oDate->format("Y-m-t");

我在这里将它包装在我的日期时间助手类中 https://github.com/normandqq/Date-Time-Helper 使用 $dateLastDay = Model_DTHpr::getLastDayOfTheMonth();

完成了

试试这个，如果你使用的是PHP 5.3+，

$a_date = "2009-11-23";
$date = new DateTime($a_date);
$date->modify('last day of this month');
echo $date->format('Y-m-d');

为了查找下个月最后的日期，修改如下:

 $date->modify('last day of 1 month');
 echo $date->format('Y-m-d');

等等。

使用Zend_Date非常简单:

$date->setDay($date->get(Zend_Date::MONTH_DAYS));

另一种使用mktime而不是date('t')的方法:

$dateStart= date("Y-m-d", mktime(0, 0, 0, 10, 1, 2016)); //2016-10-01
$dateEnd = date("Y-m-d", mktime(0, 0, 0, 11, 0, 2016)); //This will return the last day of october, 2016-10-31 :)

所以用这种方法，它会计算它是31 30还是29

有很多方法可以得到一个月的最后一天。

//to get last day of current month
echo date("t", strtotime('now'));

//to get last day from specific date
$date = "2014-07-24";
echo date("t", strtotime($date));

//to get last day from specific date by calendar
$date = "2014-07-24";
$dateArr=explode('-',$date);
echo cal_days_in_month(CAL_GREGORIAN, $dateArr[1], $dateArr[0]);