Firstly Partner A is already doing very, very well and B is doing very, very, very well. It's an awkward one, because when you're married you can view your finances as combined. There is no objective answer to this, personally I prefer treating each other like equal roommates. It is not enough to say "if fine" "I don't care", you both been to positively sit down and talk this through, talk about your values re: money, housing, expectations and responsibilities. Did either of you grow up with values to do with taking care of your partner, or looking for someone who will take care of you? Is B genuinely happy to subsidise A bearing in mind a 2:1 split in As favour of total housing costs of £1600 is effectively the same as B paying ~£300/month to A.