Interactive tables
 

How is the easiest way to create tables based on some easy calculations and allow visitors to calculate their own figures?

Say you want to calculate interest per month.

Then you allow your users to choose interest in % and their capital.

Say the enter 5% (A) and 10 000$. (B)

Then there would be a calculation that is A*B ($50) and also A*B/12 interest per month. Is there some easy way to make calculations like this? Preferbly in HTML-code or php-code.

Thanks!