How do I do this?

I need to take in some string fields from my form run them through a truth table to assign different selections a numeric value then perform a calculation containing multiplication, addition and logarithmic calculation. This will be calculating a risk priority number for each form submitted. What would the best way to do this be? Different subflows for each different type of operation? Part of the log function will also include a (current day- create date) calculation that will basically need to be updated daily as once 90 days is reached theog part of the function will start to increase the overall RPN automatically which will in turn effect the sorting (H->L) of my report rows.