An image forming apparatus includes an input unit to receive printing data, a controller to determine a duplex printing mode to be applied to the printing data from among a plurality of duplex printing modes and an engine waiting time according to a feature of the input printing data and performance of the image forming apparatus, an image processor to perform image-processing of the input printing data, and an image former to print the image-processed printing data based on the determined duplex printing mode and the determined engine waiting time.