index.php
function day_diff($date1,$date2){
// 日付をUNIXタイムスタンプに変換
$timestamp1 = strtotime($date1);
$timestamp2 = strtotime($date2);
// 何秒離れているかを計算
$seconddiff = abs($timestamp2 - $timestamp1);
// 日数に変換
$daydiff = $seconddiff / (60 * 60 * 24);
// 戻り値
return $daydiff;
}
$term = day_diff('2016-10-01','2016-12-01');