<prompt> Human: So I will try my best to explain the situation. My girlfriend and I live together. My sister wants to move in with us. For mathematical purposes we will say the rent on whatever place is 1000 per month everything included. No surprise costs. The home is a 2 bedroom 2 bath home. This means my girlfriend and I will share a bedroom and a bathroom, and my sister will have her own bedroom and bathroom. All rooms are identical in shape and size for this purpose. My reasoning: my sister gets half of the bedrooms and bathrooms in the home, with equal access to the rest of the home. She should pay half of the rent. And in a. Real life scenario 13 of utilities since utilities grow with the number of occupants. My sisters reasoning: because there are 3 people in the house and there for three incomes every one should have to pay a 3rd of every thing. Now I dont find this fair because then my girlfriend and I are getting the equal amount of the home, but paying 66 percent of the cost to live there.  <response>: I dont know how good this calculator is, but I do know it exists:But to make things simple, I would say it would be fair to do it 6040. You two the couple combined should pay 60, sister pays 40. 