We apply the method of rolling sample testing and the GARCH model to investigate the day–of–the–week anomalies in stock returns of 28 indices in major emerging and developed stock markets in the world. We find out that the day–of–the–week effects exist in both emerging and developed stock markets. We propose a single number to quantify the calendar effects performance. The conclusions based on both t–values and the calendar effect performance ratios are consistent.