A time calculating device calculates a time which a user of the device requires to run a distance such as a whole distance of a marathon race. The time calculating device is provided with a pulse frequency memory which measures pulse frequencies of the user when the user runs a given distance at least twice at predetermined different paces, and which stores the measured pulse frequencies. The time calculating device is further provided with an age input key for inputting age data of the user, and a distance input key for inputting a distance. A running speed at which the user of an age can keep running continuously is calculated from the pulse frequencies stored in the pulse frequency memory and age data input by the age input key. Further, a time is calculated which the user requires to run the distance inputted by the distance input key at the calculated running speed. The calculated time is displayed on a display unit of the time calculating device.