Calculating Months of Rest

[Corlen]

OK so I have this thing where special units need rest for so many months in my game. I have their current HP recorded in a variable at the end of a battle and their max HP recorded in another variable. I'm wondering, how would I get it so 100% HP returns 0 months needed to rest while 0% returns 5 months of rest needed. I tried getting the percentage between the two variables and then dividing it by 20 but this does the results backwards.

[AyreGuitar]

Try this:

5*(1-(HPCurrent/(HPMax+0.0))

[Corlen]

Thanks a bunch.