A device and method for estimating the charge of a motor vehicle. A device for estimating the charge of a combustion or hybrid powered motor vehicle comprising an automatic transmission, comprising a module for determining the charging of the vehicle capable of determining if the vehicle is charged and an activation module for activating a program for controlling the automatic transmission on the basis of the determination of the charging of the vehicle. The module for determining the charging comprises a first unit for estimating a first slope value on the basis of the acceleration of the vehicle derived from the driving force and the longitudinal acceleration of the vehicle, a second unit for estimating a second slope value on the basis of the moment of inertia applied to a non-driving wheel of the vehicle and the engine and resistant torques and a third unit for determining the charging of the vehicle on the basis of the first and second slope values.