A period of time over which actual reserves (of a depository institution) held at a central bank (e.g. the Fed) have to comply with or exceed the required reserve target. The requirement for any maintenance  period is usually computed as the reserve requirement for the computation period minus the vault cash held for the same period (typically 14 days). The reserve maintenance period begins 30 days after the start of the computation period (which is 2 weeks). Banks may make last-minute adjustments to make sure that their reserves meet their respective requirements imposed by the central bank.