Balances maintained to satisfy reserve balance requirements, which consist of those up to and including the top of the penalty-free band, is calculated separately for each institution and then aggregated. If an institution maintains an average level of reserve balances over a maintenance period below the top of its penalty-free band, then balances maintained to satisfy reserve balance requirements is equal to the institution's average level of reserve balances maintained over the maintenance period. For all other institutions, balances maintained to satisfy reserve balance requirements is equal to the top of their penalty-free bands. This series equals the sum of balances maintained up to the top of each institution's penalty-free band.
Board of Governors of the Federal Reserve System (US), Reserve Balances Maintained; Balances Maintained To Satisfy Reserve Balance Requirements [RBMTSRBR], retrieved from FRED, Federal Reserve Bank of St. Louis; https://fred.stlouisfed.org/series/RBMTSRBR, January 19, 2019.