Keep in mind that the broader the focus of the program, the more work is involved in actually writing it.
Writing a checkbook balancing program is relatively simple. Writing a full-featured financial planner is relatively complex.
For comparison's sake, here is a purpose statement for Quickbooks Online
, a full-featured personal accounting program:
Mastering QuickBooks 2020:
That is a very nice purpose statement, though perhaps a little broader than you want to use for this course project.
Because you are not going to sell millions of copies of your program and you do not have a team of well-paid developers to prepare a design document, you should probably narrow your focus.