If you often split the bill on anything Rent/Utilities/Drinks/etc you should check out Splitwise [0]. They have a Web/iOS/Android apps and it has been a life saver. I've used it for a little over a year now and it makes all expenses a breeze. It keeps track of who owes who what and can (when enabled) even simplify the debts so if person A owes $10 to person B and person B owes $10 to person C then Splitwise will report that person A owes person C $10.
Note: I have no affiliation with Splitwise, I just love the product.
Note: I have no affiliation with Splitwise, I just love the product.
[0] https://www.splitwise.com/