date('Y-m-d H:i:s',strtotime('+2 days'));

换个思路嘛，
你管一个月多少天干嘛呢？直接用时间戳判断不就行了？

先日期+2
然后分别判断月份，注意2月和闰年

最近学python时写的代码，仅供参考

c_day += 2

if ( c_day == 29 and c_month == 2 and not is_leap_year ) \
    or ( c_day == 30 and c_month == 2 ) \
    or ( c_day == 31 and (c_month == 4 or c_month == 6 or c_month == 9 or c_month == 11) ) \
    or ( c_day == 32 and (c_month == 1 or c_month == 3 or c_month == 5 or c_month == 7 or c_month == 8 or c_month == 10) ) \
    or ( c_day == 32 and c_month == 12 ):

        if c_day == 32 and c_month == 12: #when 12 year should increase
            c_year += 1
            c_month = 1
            is_leap_year = (c_year%400 == 0 or (c_year%4 == 0 and c_year%100 ))
        else:
            c_month += 1
        c_day = 1

http://cn2.php.net/manual/zh/class.datetime.php

$dateTime = new DateTime("now",new DateTimeZone("Asia/Chongqing"));
$dateTime->modify("+2 day");
echo $dateTime->format("Y-m-d");