Date ( Month ( FinanceStartDate ) + numberOfMonths ; day ( FinanceStartDate ) ; Year ( FinanceStartDate ) )
You can also add 1 to the year instead of 12 to the month for your "monthly" option, but the above expression can be used for all periods of you either enter a number in a data field for NumberOfMonths or set it up as a calculation field that returns different numbers based on options selected in your "Term" field.
Note also, that the above calculation may return a date near the beginning of the following month if Day ( FinanceStartDate ) is greater than 28. (Some months will not have a day 29, 30 or 31). If this is possible, you may want to modify the above calculation to return a date for the end of the month in those cases.