How to add days, weeks, months to date in PHP

Add days, weeks, months to date.

$date = date('Y-m-d');
$date = strtotime(date('Y-m-d', strtotime($date)) . ' +1 day');
$date = strtotime(date('Y-m-d', strtotime($date)) . ' +1 week');
$date = strtotime(date('Y-m-d', strtotime($date)) . ' +2 week');
$date = strtotime(date('Y-m-d', strtotime($date)) . ' +1 month');
$date = strtotime(date('Y-m-d', strtotime($date)) . ' +30 days');echo date('Y-m-d', $date);