Calculating date differences using mktime

Hi, I'm trying to figure out how to get this code I wrote to work. There is something simple that I am not apparently grasping. Basically, I have $now and $then, variables computed using mktime. $now is today's date and $then is the calendar date 90 days from $now. What I want to do is have output which reads "There are $x Months $y Days between $now and $then". I've found a bit of info online about similar stuff.. but nothing exactly like this. I tried DateDiff from phpbuilder with no success. Can someone educate me briefly on this matter to help me figure out what I'm missing? Code is below... Thanks, Kris <?php $year=date(Y, time()); $month=date(m, time()); $today=date(j, time()); $now=mktime(0,0,0,$month,$today,$year); $then=mktime(0,0,0,$month,$today+90,$year); //insert computation code that I am clueless on echo"There are $x Months and $y Days between $now and $then"; ?>