new DateTime is not working properly with the future date

I am trying to calculate the differences between 2 dates.

The first date is the reservation date, and the second date is the traveler’s birthdate. Format of the $tour_day is 15 December, 202X

$date1 = new DateTime($bir_day);
$date2 = new DateTime($tour_day);
$interval = $date1->diff($date2);

if($interval->y < 8) {
// error: Adults must be at least 8 years old
 }

It works if the reservation date is the current year.

However if the reservation date is 2022 or more, than it cannot calculate correctly because

$date2 = new DateTime($tour_day);

is always converts as 2021.

echo $tour_day; 

is ’15 December, 2023′ But

echo $date2->format('m-d-y');

is ’12-15-21′ however it must be ’12-15-23′ (12-15-23 is what I want but it shows 12-15-21)

I do not understand why the future date (next year or more) is not converting correctly but the current year of any date is no problem.

Answer

that’s because your date string is not in proper format as required by DateTime, use createFromFormat() as:

...
$tour_day = "5 December, 2023";
// your format is "Day Month, Year", so use that format as below
$date2 = DateTime::createFromFormat("j F, Y", $tour_day);
echo $date2->format('m-d-y'); // 12-05-23
...