- print_r: documentation ( source)
- gmmktime: documentation ( source)
- gmdate: documentation ( source)
<?php
$date = "20.08.2015";
$time = gmmktime(0, 0, 0, 1, 1, 1900) + ($date - 2) * 24 * 60 * 60;
print_r(gmdate("Y-m-d", $time));