A construction management system includes a construction amount data calculation unit configured to calculate, based on a current landform and a design landform of a construction site, construction amount data of the construction site, an original unit data acquisition unit configured to acquire original unit data indicating a specific condition of a work device that constructs the construction site, a construction plan data calculation unit configured to calculate, based on the construction amount data and the original unit data, a construction plan corresponding to a target construction period, and a construction cost required when construction is executed using the construction plan, and a construction plan data output unit configured to cause an output device to output the construction cost corresponding to the target construction period.