An image forming apparatus has an image carrier, a developing unit, a toner container, a pixel counter, and a used toner amount estimator. An electrostatic latent image is formed on the image carrier's surface. The developing unit feeds toner on the image carrier's surface. The toner container with a transport screw supplies toner to the developing unit. The pixel counter counts the number of pixels in toner images formed on the image carrier's surface since the toner container started being used. The used toner amount estimator estimates the amount of toner used, until the cumulative value of the number of revolutions of the transport screw reaches a predetermined number, based on the cumulative value and, thereafter, by multiplying the pixel count of the pixel counter by a coefficient. The estimator corrects the coefficient based on the pixel count as observed when the cumulative value reaches the predetermined number.