- date_add: documentation ( source)
- date_create: documentation ( source)
- date_interval_create_from_date_string: documentation ( source)
- date_format: documentation ( source)
<?php
$date=date_create("2013-03-15");
echo "date =>" . date_format($date,"Y-m-d");
echo " ******** ";
$date1= clone $date;
date_add($date1,date_interval_create_from_date_string("40 days"));
echo "date after modify date1 =>" . date_format($date1,"Y-m-d");
?>