Want to show a date calculation

I have a need to show a date calculation (date XX days in future from current date).
Can be calculated in php as:
$future_date = date("F d, Y",strtotime("+XX days"));
What construction would I need to enter into the appropriate template to show something like:
Future date is ________
Looks like I can do this with a custom phrase that I pass the $future_date variable to.
But I don't know how to create the $future_date variable and make it available to the template in the first place.