This study predicts the absolute values of heat capacities from the molecular formula per monomer for main-chaintype polymers below the glass transition temperature. The frequencies of the skeletal and group-vibration modes are calculated using the Tarasov and Einstein equations, respectively, and differences between the heat-capacities at constant pressure and constant volume are used to correct the predicted heat capacity. The contributions of skeletal vibrations to the heat capacity can be expressed by one- and three-dimensional Tarasov equations, and the contribution of group vibrations can be determined by summing the group-vibration heat capacities for functional groups and atoms constituting the monomer as obtained from the Einstein equation. The absolute value of the heat capacity is predicted from this combination of equations. The heat capacities of poly(1,4-butylene adipate) are predicted within an error range of ± 3.0 % from 80 to 200 K.