Extract/Summarize Table Data

I have to keep track of an IOLTA account (Lawyer bank account for holding client money). My firm has clients who give us retainer checks that go into the IOLTA account, and then as we do work for the client, we bill them and move the money from the IOLTA to our operating account. Sometimes we have to return some of the money if we haven't billed for it.

I have to keep track of what is in the account and which client it belongs to. I was wondering if there is a function to extrapolate which client still has money in the account. I have attached a simple example of what i want to do, but i would like to have the table on the left automated if possible.

Thanks!