I'm preparing to buy my 2nd (and hopefully forever) home. I made calculations and can additionally save the difference from my current mortgage payment to the expected new one (current 1200e, expected new 2000e, so I'll be saving 800e every month). Is it better to just save this 800e to separate savings account and use it as clear proof that I can afford the new mortgage or should I use it to overpay my existing mortgage? I'm guessing that overpaying is helping us directly by lowering debt and interest, but cash (or easily accessible deposit) is always good to have? Any 'rule of thumb' in this case?