An operating method of an image forming apparatus including estimating an accumulative usage of toner in a toner cartridge, determining initial remaining life information of the toner cartridge and indicating a remaining amount of the toner based on the estimated accumulative usage of the toner, obtaining weight information indicating a first weight of the toner cartridge at a first time point at which the remaining amount of the toner is within a predetermined range, determining a correction factor indicating an error factor between the estimated accumulative usage of the toner and an actual accumulative usage of the toner, based on the obtained weight information and the estimated accumulative usage, and correcting an amount of toner to be used in an image forming operation to be performed after the first time point based on the correction factor, and determining adjusted remaining life information based on the correction factor.