<prompt> Human: Hi PF,My girlfriend who I live with recently got a job at the company I work at. The carpool commute is nice because we are both going to the same place. I am unsure, however, about what the cost should be. I bought my car a while back and am about halfway through paying it off. As such, I have car payments, car insurance, and gas which I pay regularly. Since my girlfriend is making use of my car every day, I thought it would be fair for her to help me pay some of these costs. She, however, doesnt see it as fair that she should help me make car payments without getting any equity in the car herself should we break up or something which isnt unreasonable. I, however, am eating a large cost every month for transportation while she pays nothing for transportation. Has anyone been in a situation similar to this before? What is fair? Thanks!  <response>: If you live together, youre already hopefully in the habit of splitting expenses. It is not important, necessarily, that every single expense that benefits both of you be split much less exactly down the middle, and in fact even if every single shared expense is split that still doesnt guarantee similar expense for similar benefit.Two things to consider:1. Youd be making this drive anyways, and the increased expense of having your girlfriend along with you is negligible.2. Since shes commuting to work with you, shes not having to buy gas nearly as often for her own vehicle.One way to resolve this would be for her to chip in for gas every so often. Another way would be for her to treat the both of you to dinner once or twice a month. Another way still would be for you to simply eat the costs as you would have to if you were commuting by yourself to work.Before my wife and I got married, we lived together. I made substantially more than she did, so I paid the majority of household expenses we didnt figure out exact percentages. From a superficial view, this seemed unfair. But my costs were about the same as theyd be if I lived by myself, and she didnt have to be like most of her coworkers and have a second full-time job to supplement her first full-time job neither non-profits nor public schools pay particularly well. It seemed a small price to pay to be able to have more time together. 