date_default_timezone_set('prc');

//获取添加的月个数
$months=$request->input('months');
//设置默认时区北京
        date_default_timezone_set('prc');
        //处理添加月
        if (date("n") + $months >= 12) {
            $tmpMonth = date("n") + $months - 11;
            $tmpYear = date ("Y") + 1;
            $tmpDay = date("d");
            $tmpH = date("H:i:s");
        }else{
            $tmpMonth = date ("n") + $months;
            $tmpYear = date ("Y");
            $tmpDay = date("d");
            $tmpH = date("H:i:s");
        }
        $tmpDate = "$tmpYear-$tmpMonth-$tmpDay $tmpH";

<?php
$m = intval($_GET['months']);
echo date("Y-m-d H:i:s",strtotime("+ $m months"));