<prompt> Human: Hi All, Due to a complicated family situation, my wifes sister is moving in with us. For the next 4 months shell be staying every other week, and after that every week.We have an extra room were not using, and both me and my wife are happy with the arrangement. Were not trying to make money from this, but we do want to cover any additional cost that is imposed on us because of her moving in. We are all in agreement that our expenses should not go up because of her. The sister in law is willing to help out in the house, i.e. chores.My sister in law has asked us to figure out the amount she should pay us monthly. what is the best way of doing this? a standard fee? a fee to cover water electricity, with her buying her own food? whats the easiest way to figure out what that amount would be?Edit:Not trying to charge her rent. Were okay with her staying rent free. We just want her to pay the additional cost to waterheatingfoodother costs.  <response>: Take all your expenses on utilities and food, thats what you and your wife spend on it. Divide that sum by 2, thats hypothetically what one person would spend on it. That amount would be very reasonable to charge assuming she doesnt buy food for herself, if she does, only use utilities. 