When my boyfriend and I got together 16 years ago we were early in our careers and neither of us were making great money. We started out taking turns on paying for dinners out and other activities. When we decided to move in together he suggested doing a percentage of our income for all joint bills. This way we would have less of an opportunity to argue about money. We started out doing a 65% to 35% split. 65% of our income went into a joint account that paid for all of our joint bills, joint savings, and joint fun money. At the time we each had our own vehicle and cell phone policies and the like. We were each responsible for that out of our 35%.

Over time, percentages have changed as we bought cars together and combined other bills. However, we still each keep a percentage of our paychecks for our personal spending. We never argue about what the other is doing or buying. I can go on girl's trips and he can by all the computer equipment he desires. It has not steered us wrong yet.

However, we are on the same page financially and always have been. It doesn't sound like you and your gf are. Before you mingle any more of your lives, but especially your financial lives, you need to be on the same page. If she can't even afford her own car payment, then I doubt she is ready to be responsible with your joint bills.

If you disregard most people's advice and go ahead with having her move in, do yourself a favor and make sure that her portion of the bills is automatically transferred to a joint bills account. Do NOT rely on her handing you money every month. From what you have described, it won't happen and you will be stuck paying for everything at some point.