Adding one day to a date

My code to add one day to a date returns a date before day adding: `2009-09-30 20:24:00` date after adding one day SHOULD be rolled over to the next month: `1970-01-01 17:33:29` <?php //add day to date test for month roll over $stop_date = date('Y-m-d H:i:s', strtotime("2009-09-30 20:24:00")); echo 'date before day adding: '.$stop_date; $stop_date = date('Y-m-d H:i:s', strtotime('+1 day', $stop_date)); echo ' date after adding one day. SHOULD be rolled over to the next month: '.$stop_date; ?> I have used pretty similar code before, what am I doing wrong here?