3v4l.org

run code in 300+ PHP versions simultaneously
<?php $data = strtotime("first day of this month"); echo $data; echo strtotime($data . " -1 year");
Output for 5.5.0 - 5.5.38, 5.6.0 - 5.6.40, 7.0.0 - 7.0.33, 7.1.0 - 7.1.33, 7.2.0 - 7.2.3, 7.2.5 - 7.2.33, 7.3.0 - 7.3.33, 7.4.0 - 7.4.33, 8.0.0 - 8.0.30, 8.1.0 - 8.1.28, 8.2.0 - 8.2.18, 8.3.0 - 8.3.6
1451656429
Output for 7.2.4
1451656430

preferences:
165 ms | 401 KiB | 330 Q