<?php
// 測定開始日
$start_day = strtotime('2016/04/23');
$today = strtotime( date('Y/m/d') );
$count_week = 8;
//終了日を出すために週に+1
$count_end = $count_week + 1;
$i = 0;
$ret = array();
$ret2 = array();
while( $count_end >= $i ){
	$ret[$i] = strtotime( $i.'week', $start_day);
	$ret2[$i] = date('Y/m/d' ,strtotime( $i.'week', $start_day));
	if( $i >= 1){
		$range_start = $ret[$i - 1];
		$range_end = strtotime( '-1 day', $ret[$i]);
		if( in_array($today, range( $range_start, $range_end ) ) ) echo $i."週目に該当<br>" ;
	}
	$i++;
}
print_r($ret);
print_r($ret2);
?>

<?php
$start_day = strtotime('2016/04/21');
$add = 7*8;
// カレンダー作成
$week_count=1;
$ary=array();
for($i=0; $i<$add; $i++)
{
	$buf = strtotime($i. ' days', $start_day);
	$ary[date('Y/m/d', $buf)]['date'] = date('Y/m/d', $buf);
	$ary[date('Y/m/d', $buf)]['w'] = date('w', $buf);
	if($i%7==0 and $i!=0) $week_count++;
	$ary[date('Y/m/d', $buf)]['week_count'] = $week_count;
}
print_r($ary);

// 該当日抽出
$today = date('Y/m/d');
if(array_key_exists($today, $ary)){
	print_r($ary[$today]);
}
?>

なるほどー。