Converting Date Format for Calculations in PHP
===

I'm displaying a due date for tasks in an m/d/y format. I'm displaying the day the task was posted in a "Posted X $name(s) ago" (eg. "Posted 6 day(s) ago").

I'm working on giving the timestamps (posted and due date) different CSS classes, depending on how many days there are from TODAY until the due date. (So the "Posted X" timestamp is less relevant, I just wanted to give a better picture.)

So far, I have the following down:

    $cdate = $this->data['due'];
    $today = time();
    $dovi = date('m/d/Y', $today);
    $difference = $cdate - $dovi;
    $upcoming= floor($difference/60/60/24);

$cdate is pulling the due date from the DB, in m/d/y format. $today is telling us what today is (using the UNIX timestamp). $dovi is converting time() in to the m/d/y format. $difference is telling us the difference between today and the due date. $upcoming, in theory, should take that difference and dumb it down into a simple number.

I think that for the calculation to work, I would need to convert $cdate in to a UNIX timestamp or somehow convert both $today and $cdate into some other matching format other than m/d/y. 

Does anyone have suggestions on the best way to make this work? I already have some code to run the CSS changes, the only thing I'm stuck on is this conversion/calculation issue to determine how many days from NOW (time()) the due date is. Thanks!!