Calculated Fields

After having searched for a while and talked to Pipedrive support I'm a little bit lost when it comes to calculated fields which don't seem to exist.

My scenario is that I'm storing a contract length in months, a setup fee and a monthly fees in different custom fields. I'd love to calculate the total contract value (aka. duration x monthly fees + setup fees). Unfortunately there doesn't seem to be a way to do this in Pipedrive.

What other solutions are out there? How have you solved similar problems?