increament for loop by date php : I am trying to increament date by new date. but it is not showing any result.

                $ed = strtotime($endDate);
				for($i = $ed; $i <= strtotime($today); $i = $ed ){
					$toArray['d'] = $ed;

					$startDate = date('y-m-d', strtotime("+1 day", strtotime($endDate)));
					$endDate = date('y-m-d', strtotime("+13 day", strtotime($startDate)));
					$ed = strtotime($endDate);

				}


it is not working . whats wrong..?