Recursive calculations can be used, but only if you have an if, case or other function that will terminate the recursive references when the end of the chain is reached
Wouldn't it make more sense to compute a total due over all semesters for a given family? That can be done without using a recursive function. A summary field or a sum function can be used to compute that total by using an added relationship to a new occurrence of an existing table where you match fields only by FamilyID instead of by FamilyID and SemesterID.
Many thanks. I set up a table occurrence of FamilyUpToCurrent which requires the familyID to be equal but the semesterID is less than or equal to the Family's semesterID. Then in this table occurence I found sum( TotalCharged) - sum( TotalPaid) and this seems to do the trick for the TotalDue. I left the variable of PreviousTotal by itself since it is useful to display, even if I can't easily do computations with it.