Over payment Graph

A couple of my firms who are thinking about moving over from IRESS to SOURCE have expressed as part of their compliance process they produce an 'Over Payment Graph' which they send to the customer to show how quickly the loan would be paid off if they overpay their Mortgage by £250 for example. Whilst this isn't a standard compliance procedure in every firm I have found more and more use this function. *Please find attached a copy of the IRESS over payment graph. How easy would this be to build on our side?