An image forming apparatus includes an image carrier, a developing roller, and a control unit. The image carrier has a surface on which an electrostatic latent image is formed. The developing roller is arranged to face the image carrier to form a development nip between the image carrier and the developing roller. The developing roller supplies toner in a two-component developer carried on a surface of the developing roller to the image carrier in the development nip so as to develop the electrostatic latent image. The control unit drivingly controls the image carrier and the developing roller. The control unit discharges the toner in the development nip to the image carrier in a state where the developing roller is stopped, so as to calculate a toner concentration in the two-component developer based on an amount of discharged toner.