Add number of days to a date

I want to add number of days to current date:
I am using following code:

$i=30;
echo $date = strtotime(date("Y-m-d", strtotime($date)) . " +".$i."days");

But instead of getting proper date i am getting this:
2592000

Please help me on this

Thanks,

Pankaj

Add number of days to a date