I think there are a few issues here, the main one being suiting your long term plans rather than solving a short term issue. Surely, continuing the current arrangement is helping you to save money (for your 'real' house ) as at least a third of the mortgage and bills is being furnished by the brother? Also, when you do buy your 'real' house you will benefit from FTB reliefs for longer and maybe get more benefit for your FTB relief as presumably the 'real' property is going to be costing more in interest? Like Clubman says it's whatever is right for you at the end of the day... I took the option of solving a short term problem by buying with a view to moving on quickly and I ended up with claw hands.