<?php
$period = new DatePeriod(
new DateTime('2015-01-01'),
new DateInterval('P1M'),
new DateTime('2019-01-01')
);
var_dump($period->getDateInterval()->m);
Warning: PHP Startup: Unable to load dynamic library 'sodium.so' (tried: /usr/lib/php/8.3.5/modules/sodium.so (libsodium.so.23: cannot open shared object file: No such file or directory), /usr/lib/php/8.3.5/modules/sodium.so.so (/usr/lib/php/8.3.5/modules/sodium.so.so: cannot open shared object file: No such file or directory)) in Unknown on line 0
int(1)