An organic light emitting display device includes a timing controller, data driver, and a plurality of pixels. The timing controller outputs gamma voltages corresponding to image data. The data driver generates data signals based on the gamma voltages. The pixels emit light with brightness corresponding to the data signals. The timing controller includes an on-pixel ratio (OPR) operator to calculate an OPR based on the image data and a gamma voltage supplier to select one of a plurality of gamma tables based on the OPR and to output gamma voltages stored in the selected one of the gamma tables.