Method for determining a torque (Ce) in a transmission chain of a motor vehicle, in which use is made of a transmission chain comprising an input shaft (4a, 4b) intended to be coupled to an engine of the motor vehicle, an output shaft (7a, 7b) intended to be coupled to drive wheels of the motor vehicle, and a gearbox comprising a plurality of synchromesh gears (8a, 8b) able to respectively couple the output shaft to the input shaft in a plurality of transmission ratios, the method comprising: measuring a speed of rotation (Wp) of the input shaft, measuring a speed of rotation (Wv) of the output shaft, providing a digital model implemented by computer (32a, 32b) that simulates the transmission chain by a torsionally deformable system, the digital model comprising a torsional stiffness coefficient (kt) of the deformable system, a torsional viscous-damping coefficient (It) of the deformable system and a plurality of state variables representing an instantaneous state of the torsionally deformable system, in which the state variables are chosen from the set consisting exhaustively of: the speed of rotation (Wp) of the input shaft, the speed of rotation (Wv) of the output shaft, the input torque (Ce) acting on the input shaft, the time derivatives and integrals of all orders of the preceding variables, and the combinations of the preceding variables and of their time derivatives and integrals of all orders, and in which the state variables comprise an output variable (Ŷ) chosen from the set consisting of the speeds of rotation (Wp, Wv) of the input shaft and of the output shaft, the time derivatives and integrals of all orders of the speeds of rotation of the input shaft and of the output shaft, and the combinations of the speeds of rotation of the input shaft and of the output shaft and of their time derivatives and integrals of all orders, calculating the state variables of the digital model at successive instants by converging the output variable (Ŷ) with the measured speeds of rotation of the input shaft and of the output shaft, and determining the input torque (Ce) acting on the input shaft at successive instants as a function of the calculated state variables. measuring a speed of rotation (Wp) of the input shaft, measuring a speed of rotation (Wv) of the output shaft, providing a digital model implemented by computer (32a, 32b) that simulates the transmission chain by a torsionally deformable system, the digital model comprising a torsional stiffness coefficient (kt) of the deformable system, a torsional viscous-damping coefficient (It) of the deformable system and a plurality of state variables representing an instantaneous state of the torsionally deformable system, in which the state variables are chosen from the set consisting exhaustively of: the speed of rotation (Wp) of the input shaft, the speed of rotation (Wv) of the output shaft, the input torque (Ce) acting on the input shaft, the time derivatives and integrals of all orders of the preceding variables, and the combinations of the preceding variables and of their time derivatives and integrals of all orders, the speed of rotation (Wp) of the input shaft, the speed of rotation (Wv) of the output shaft, the input torque (Ce) acting on the input shaft, the time derivatives and integrals of all orders of the preceding variables, and the combinations of the preceding variables and of their time derivatives and integrals of all orders, and in which the state variables comprise an output variable (Ŷ) chosen from the set consisting of the speeds of rotation (Wp, Wv) of the input shaft and of the output shaft, the time derivatives and integrals of all orders of the speeds of rotation of the input shaft and of the output shaft, and the combinations of the speeds of rotation of the input shaft and of the output shaft and of their time derivatives and integrals of all orders, calculating the state variables of the digital model at successive instants by converging the output variable (Ŷ) with the measured speeds of rotation of the input shaft and of the output shaft, and determining the input torque (Ce) acting on the input shaft at successive instants as a function of the calculated state variables.