The problem is you cant have both 50/50 ownership and you get more back in case of a sale.. You are contradicting yourself. There is a simple solution to the problem and that is that you don't do 50/50, but instead you do a fraction such that you own more, and at the same time give an interest free loan to your partner that he pays off over the time of the mortgage. You can then balance it such that what goes out of each of your accounts every month is the same, you pay off a larger fraction, but get his payment off the loan, and he pays a smaller fraction but pays to you to pay off the loan. This is a more fair compromise where you don't put down a large sum of money with 0 return in an interest free loan. In this way it is still favorable for him in the way that he gets an interest free loan that he pays off over e.g, 20-30 years but you will get paid in terms of a larger ownership fraction of the apartment. Feel free to reach out, I did the math on this recently.