If I am living with a couple I would pay 33%. Or if someone is living with me (Suppose I am one of the couple) I would ask him to pay 33%. This is because we are sharing the expenses. you cant say we couple are using one room so we will pay only 50% in total. it is obvious that you couple will sleep together. You cant say we are couple so pay 50% for grocery. Because you couple don't eat only 50% but eat 66%in total. You cant say you will pay 50% of electricity because, of course both of you use electricity. You can say I will pay 50% for water because both of you will use water. But of Course you "might" want to say i will not pay 66% for heat because couple dont need much external heat to heat themself (Just kidding) then how do you feel that a couple does not have to pay 66%.