I have already written an app for this as I am a property developer with 50 properties. I also was a consultant C++ developer for 12 years so I wrote the app in an afternoon. I have 3 version of the app in Java, C++ & C#. I know nothing of the procedure for your development but I think a mortgage repayment app is useful. Whoever is reading this probably wants to buy a house at some point and would use the app. Try looking for this app on the internet and there are lots of free versions but these versions are polluted with add on expenses and custom bank charges. That is why I wrote my own version.