- date: documentation ( source)
- strtotime: documentation ( source)
<?php
$newSettleDate = new DateTime(date('Y-m-d H:i:s'));
$newSettleDate->modify('+2 weeks');
$newSettleDate->modify('Next Sunday');
echo $newSettleDate->format('Y-m-d H:i:s');
echo strtotime('next sunday', date('Y-m-d H:i:s'));