Abstract: In a method for operating an internal combustion engine, a control operation is provided for the combustion process, wherein an actual value of the crank angle of a 50% mass conversion point of the fuel to be converted during the combustion is determined taking into account a measurement signal of an ion current sensor which is arranged in a combustion chamber, and the crank angle of the 50% mass conversion point is adjusted to a set point value of the position of the 50% mass conversion point by varying at least one manipulated variable of the internal combustion engine which affects the combustion. The crank angle of the 50% mass conversion point is determined in a layered neural network in which the measurement results of the ion current sensor are logically combined with at least one further, continuously measured operating parameter of the internal combustion engine.