103 CMR, § 405.09
The Department shall maintain an account with the State Treasurer that consolidates all FAs, regardless of the type of funds, for each I/I or C/C in the custody of the Department in order to maximize interest income; the Department shall award interest as required by M.G.L. c. 127, §48A, and may award interest on all other monies whenever feasible. The Department shall credit each active FA account with interest earned. Interest earned by and not credited to inmate personal accounts shall be credited to a Department account(s) and utilized for inmate benefit. To be credited with interest income for the current period, an account must be active in the system the day the interest is posted. The calculation for the distribution of interest and the posting of interest to all accounts will be accomplished via the FAS.
103 CMR, § 405.09