This is something I find myself needing to do quite frequently. You deal with UK dates as input and output of a system but somewhere in the middle they need to convert to US dates.

A quick way to shove a UK Date into a US format is to to an explode on the UK date by whichever separator it is using (normally '/', sometimes '-') then glue the bits back together with the second element swapped with the first (moving month and day around).

I have compiled this into a quick method:

/**
* A very simple function to change the date from the UK
* format to the American format.
*
* @param string $uk_date Assumed to be in the format day month year
* @param string $separator_input What divides the date up goung in.
* @param string $sepatator_output What divides the date up going out.
*
* @return string The date formatted to suit the US formatting.
*
* @author Toby Osbourn 
*/

function makeUSDate($uk_date, $separator_input = '/', $sepatator_output = '/')
{
    list($day, $month, $year) = explode($separator_input, $uk_date);
    return $month.$sepatator_output.$day.$sepatator_output.$year;
}

This is also part of my Useful PHP Functions file on Github.