An image forming apparatus includes a supply unit and a control unit. The supply unit supplies a recording agent to a storage unit from a recording agent cartridge. The control unit is configured to at least one of (i) estimate a discharged amount of the recording agent discharged from the recording agent cartridge to form an image based on (a) a running amount of the supply unit used to form the image and (b) an additive characteristic of the additive added to the recording agent or (ii) estimate a supply amount to be discharged from the recording agent cartridge by the supply unit to form the image based on (a) the running amount of the supply unit necessary to form the image and (b) the additive characteristic of the additive added to the recording agent, and cause the supply unit to run based on the supply amount.