PHP date_sub() Function

Subtract 40 days from the 15th of March, 2013:

<?php
$date=date_create("2013-03-15");
date_sub($date,date_interval_create_from_date_string("40 days"));
echo date_format($date,"Y-m-d");
?>

Definition and Usage

The date_sub() function subtracts some days, months, years, hours, minutes, and seconds from a date.

date_sub( object, interval)

Parameter	Description
object	Required. Specifies a DateTime object returned by date_create()
interval	Required. Specifies a DateInterval object

Return Value:	Returns a DateTime object on success. FALSE on failure
PHP Version:	5.3+