An electrically operated aerosol-generating system for receiving a liquid aerosol-forming substrate and a main unit and a cartridge for an electrically operated aerosol-generating system. The aerosol-generating system includes a liquid storage portion configured to hold a liquid aerosol-forming substrate; an aerosol generator configured to receive liquid aerosol-forming substrate from the liquid storage portion; one or more capillary wicks configured to transfer liquid aerosol-forming substrate from the liquid storage portion to the aerosol generator; a tilt sensor configured to sense the orientation of the liquid storage portion; and electric circuitry. The electric circuitry is configured to monitor the orientation of the liquid storage portion as sensed by the tilt sensor and determine depletion of liquid aerosol-forming substrate based on the orientation of the liquid storage portion.