mktime to determine specific future date

I am writing a calendar script and having trouble figuring out how to use mktime to determine the date x number of days from current date. Currently, the script below outputs the current date. I want it to also output "90 days from now is (date 90 days from now)". I'm a little confused on how to do this and have read the help page already, tried a few things.. no luck. Any ideas out there? /* GET TODAY */ $year=date(Y, time()); $month=date(m, time()); $month_text=mktime(0,0,0,$month,1,$year); $month_text=date(F, $month_text); $today=date(j, time()); /* insert code to determine date 90 days from current date and assign value to $ninetydays */ echo"Today is $month_text $today, $year<p>"; echo"90 days from now: $ninetydays";