In scheduling building construction work, non-workable days due to weather conditions and national holidays lessen the accuracy of scheduling. This study aims to determine the percentage of workable days to enable more accurate scheduling of superstructure work in building construction. To calculate the percentage of workable days applicable to superstructure work in building construction, this study analyzed various data, including actual building cases. Actual weather data in the Seoul region for the past five years was used in particular and the number of national holidays therein was analyzed. This approach is intended to yield a more accurate and objective percentage of workable days. This study suggests that the use of yearly and monthly percentages of workable days in the scheduling for superstructure work of future building construction projects will make scheduling more objective and accurate.