Find number of days between given two days in PHP

We are going to study how can we calculate the number of days between given two days. For the example I am going to find the number of days between current date and another given date.

<?php

    $year="1990";
    $month="March";
    $day="23";

$today=date('Y-m-d'); // in-built function to get current date.

$datetime1 = date_create($year.'-'.$month.'-'.$day); //Given date
$datetime2 = date_create($today); //System date for current date
$interval = date_diff($datetime1, $datetime2); //$datetime2 - $datetime1
$date_amount= $interval->format('%R%a');
echo($date_amount);

?>