I remember a similar situation which happened to me and another friend. We were living with a couple in a three bed room and we were sharing everything four ways (even grocery in the beginning which we discontinued after a month or two). However, after living together for 1 and half years, the couple decided that we should only redo the lease if we split the costs 3 ways (for rent). Like the points mentioned above, they forgot about some things (the effect of which was rather cruel): 1) All of us had a similar income level. This way, we'd have a hard time making ends meet. 2) The different usages of electricity etc. 3) Common sense. The big difference between our cases though is that we talked about what we wanted to do in the future rather than trying to change the arrangement in the middle. However, I do feel that in choosing between 50:50 and 1/3rd deal, the 1/3rd deal is definitely more fair. Jaya