您可以比较添加1个月之前和之后的月份。如果不一样，您超出了下个月。
function add($date_str, $months)
{
$date = new DateTime($date_str);
// We extract the day of the month as $start_day
$start_day = $date->format('j');
// We add 1 month to the given date
$date->modify("+{$months} month");
// We extract the day of the month again so we can compare
$end_day = $date->format('j');
if ($start_day != $end_day)
{
// The day of the month isn't the same anymore, so we correct the date
$date->modify('last day of last month');
}
return $date;
}
$result = add('2011-01-28', 1); // 2011-02-28
$result = add('2011-01-31', 3); // 2011-04-30
$result = add('2011-01-30', 13); // 2012-02-29
$result = add('2011-10-31', 1); // 2011-11-30
$result = add('2011-12-30', 1); // 2011-02-28
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