Try this...
<?
$stringdate = "2003-04-01";
$timestamp = strtotime($stringdate) - 60*60*24;
$year = date("Y", $timestamp);
$month = date("m", $timestamp);
$day = date("d", $timestamp);
echo "String date : $stringdate<BR/>\n
Timestamp : $timestamp<BR/>\n
Year : $year<BR/>\n
Month : $month<BR/>\n
Day : $day<BR/>\n
New date : $year-$month-$day<BR/>\n";
?>