In a financial institution accounting system, a system for, and method of, determining an optimal sweep threshold parameter for a demand deposit account ("DDA"), the DDA having a sub-DDA contra-account and a sub-money market account ("sub-MMA") associated therewith. The system includes: (1) an initialization routine that sets a trial sweep threshold parameter equal to a value that is a function of an activity of the DDA during a historical period of time and (2) a trial sweep routine that performs a trial sweep process on the DDA during the period of time, a timing of sweeps from the sub-MMA to the sub-DDA occurring during the trial sweep process being a function of the trial sweep threshold parameter, the sweep routine repeated with a modified trial sweep threshold parameter until modification of the trial sweep threshold parameter fails to produce an increase in an average balance of the sub-MMA for the predetermined period of time, the trial sweep threshold parameter thereby determined to be an optimal sweep threshold parameter for the DDA.