Am I completely liable for the difference when a roommate overpays me for rent?

Yes, since you collect the money and commingle it, and then pay the bills out of all the collected and pooled money, you are responsible and liable.

Now how to solve the problem:

You can pay her back the overages right now. All done, she’s happy, just go on.

OR

You can tell her, “yes, I owe you that, but since I don’t keep that close of a watch on my total account, I don’t have the extra right now. Let’s work out a solution.”

And then you can figure out how to fix it. You don’t say how much she overpaid. A couple ideas though are to have her deduct it all from next months total, or if that is too big a hit, over the next, say, three month’s totals. You need to determine how much you can cover each month, and from that see if you can work out a similar time for her.

It maybe a bit painful to be real close on your money for a couple months, yet it will work out best in the end.

Pay her what you owe her. If you don’t it will get ugly.

You should definitely pay her the amount she overpaid, but you should discuss with her that you don’t have a pile of her extra cash lying around, so the reimbursement may not be immediate.

And you should include an amount per person in the future payments to compensate you for the time you spend collecting and accounting for the funds, in addition to the risk that you have for over and under payments. You will probably want to be completely open and transparent about that, but you don’t need to feel guilty if you choose not to, either. Your flat mates are getting a service from you, after all, and you deserve to be compensated fairly – or at “whatever the market will allow” – and good for you if you do that.

I would just adjust it by reducing the amount she needed to pay either in the next month or over the next two months.

But, that is just me.

Can you give us an idea how much we’re talking about?

hey thanks guys for the responses. I posted this before class and just got home. So she overpaid about 60 bucks for two months and it comes out to about 125ish. I can afford more like 30 a month. she would prefer the money over two months though as she is unsure whether or not she’ll be here in four

It sounds like you need to do a better job of keeping a ledger in each person and notice if someone has a gredit or a debit. Since the other residents benefited from her over payment, I would thing that they should share the responsibility to pay her back.

yeah I agree I need to increase the level of detail in my spreadsheets. and the amount falls on me because the spreadsheet only calculates bills. thanks everyone for the responses I think I will propose the 30 each month with a buyout clause if she moves out before the three months

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You could also just put that extra money toward her current amount due. The next month she owes for, she just pays that much less.

I seriously hope all of these bills are not in your name… And I believe you should have a separate account for just house rent/bills with that many people involved. Do not mix your personal $ with house $. “Being a broke, full-time student” does not give you a reason to be irresponsible with your (and others) finances.
That being said, how did you end up the appointed bookkeeper to begin with? It does seem like you are being taken advantage of, most likely from other “broke, full-time students.” You mentioned bills change because of long term house crashers, which of course would alter water usage and to some extent, electricity (although in a house with that many people, no doubt everything is always on). I propose a flat rate for the crasher, ABOVE and BEYOND everyone’s regular bills. Keep the fluctuations for long-term housemates to a minimum. If a couch surfer doesn’t want to pony up some $ for being there they should leave. Put the extra $ in the same account to help cover those fluctuations, keep a flat rate on regular tenants, save yourself headache. Once there is a nice chunk of “extra $” in the account, use it to buy something for the common good, like toilet paper, dish or laundry detergent.
To re-cap: Stop using the account for your own money, agree on a flat rate that is fair and covers bills to save yourself that time and headache. Insist upon an agreed upon “crash fee” for long term guests that is beyond the base needs, and when $ has grown, use it to help the whole house out.

One more thing… To calculate what would be fair use your past spreadsheets to find an average and base rate per permanent renter. Because the overpaying roomie might not be here in 4 months leads me to believe the whole house is teetering without lease agreements. I’m sure at least one person is ultimately responsible, and again, I hope it isn’t you.

I agree with @GloPro with one exception. Everyone should agree that you either get a percentage of every months income as a fee for your hard work or you get a reduction in your rent.