An image forming system, having a recording head, a sheet conveyer, an inverting mechanism, and a controller, is provided. The sheet conveyer conveys a sheet in a sheet-conveying direction. The sheet is nipped at nipping points located at positions upstream and downstream in the sheet-conveying direction with respect to a discharging position. The inverting mechanism inverts the sheet from a first side to the second side. The controller determines an initial arrangement of the sheet in the sheet conveyer where image-forming on the second side starts, and controls a length of a period between time, when image-forming on the first side of the sheet in the posture with the first side facing the recording sheet is completed, and time, when the image-forming on the second side of the sheet inverted and refed to the sheet conveyer starts, based on the determined initial arrangement of the sheet in the sheet conveyer.