An image forming apparatus includes a recording head, a controller, a first detector, and a second detector. The controller calculates a viscosity of ink in each of nozzles based on a temperature, a humidity, and an elapsed time. The controller determines, among the nozzles, a nozzle in which the viscosity is equal to or higher than a threshold to be a high-viscosity nozzle. The controller acquires non-ejection information indicating an ejection disabled nozzle that is disabled to eject the ink. The controller acquires a viscosity of the ink in the ejection disabled nozzle. The controller calculates an average value of viscosities of the ink in the plurality of nozzles. The controller compares the viscosity of the ink in the ejection disabled nozzle with the average value of the viscosities of the ink in the nozzles. The controller determines whether or not to change a contribution value based on a comparison result.