How to calculate the 30 days after the class start date – in a form? in a workflow?

I have a requirement to build a form that will route through several approval steps and will automatically terminate when 30 days after the 1st day of class has been reached.  This form has been built in InfoPath and the workflow will be written with SharePoint Designer.

I am trying to determine the best way to calculate the 30 days after the class start date – in the form? in the workflow? as a calculated column in a list that could be used as a data connection for the form?

I currently have two SharePoint lists that have pieces of the data I need (Semesters and Part of Term)

I need the start date for each Semester/Part of Term combination (there are 3 semesters each academic year, numbered 201412, 201414, 201416), for each Semester there are 14 possible Parts-of-Term (Full Term, 1st 5 weeks, 1st 7.5 weeks, 1st 10 weeks, etc.)

We work with 5 local high schools to offer dual-enrolled courses according to the base high school’s calendar (meaning that their start dates are different from the “standard calendar”).

What this means is there are theoretically, 14+ start dates for a course in any given semester.

I need to be able to pull into a form/workflow is the the start date for the given course + 30 days.  So that I know when to terminate the workflow.

I am open to suggestion on this and would greatly appreciate any input.