Doing math in workflows

It would be helpful if in your workflows you could do math.  For example we have a workflow that creates a new deal in the renewal pipeline for every contract that is invoiced.  For most of the contracts simply adding a due date of 365 days (1 year contract length) is good enough.  However, some of our customers have a 3-5 year length which we have defined in a custom "Contract Length".  Ideally you would be able to have a workflow that could do something like $Close_Date + $Contract Length = $Due_Date.

 

I could see other uses for this as well, but this is the immediate one that comes to mind.

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