Mutual fund sub accounting is a way to "clear" (the process of buying and selling) the mutual fund transactions. An intermediary record keeps all of the individual shareholder account information, such as the individual balances and individual transactions and dividends in each fund. The account balances roll up to match an omnibus account balance that is record kept by the transfer agent of the fund. When individual investors buy or sell a particular fund those transactions the intermediary combines those transactions and a minimum number of larger trades are placed with the fund in the omnibus account.