<?php
$startDateTime = new DateTime('2016-10-17');
$currentDate = new DateTime('2017-2-5');
//$startDateTime->modify('+1 day');
$currentWeekNumber = $currentDate->format('W') + (($currentDate->format('o') - $startDateTime->format('o')) * 52);
//Subtract the start week from the current week (and add 1, since we start at Week 1) to find the current study week
echo $currentWeekNumber - $startDateTime->format('W') + 1;
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
16