Retrieving dates as day,month and year wise in PHP

To Get the date from the current date as per day,month,year wise:
 

     
//current date in Y-M-D Format.
            $now=date('Y-m-d');       


// Retrieveing date from the current date by day wise .(For ex., retrieved 6 days before from current date).
	    $cal_day=date('Y-m-d',strtotime("-6 days"));       

// Retrieveing date from the current date  by month wise.(For ex., retrieved 1 month before from current date).
	    $cal_month=date('Y-m-d',strtotime("-1 month"));

// Retrieveing date from the current date  by year wise.(For ex., retrieved 1 year before from current date).
	    $before_year=date('Y-m-d',strtotime("-1 year"));