An elevator counterweight (2) includes a first part (4). The first part (4) is configured to be connected, in use, to a suspension member (8) of an elevator system (1). The first part (4) is arranged to receive an additional mass (6) when the first part (4) is connected to the suspension member (8), such that a mass of the elevator counterweight (2) can be varied. A controller (14) may be arranged to control a mass variation system (12) to vary the mass of the elevator counterweight (2) according to a schedule. The controller (14) may determine the schedule in a learning process.