The disclosure relates to a method for operating a fuel cell system and a correspondingly configured fuel cell system, comprising a fuel cell stack, an anode supply with a hydrogen reservoir, an anode supply path connecting the hydrogen reservoir to the fuel cell stack, a recirculation path connecting a fuel cell outlet to the anode supply path, and a conveying device for conveying recirculated anode exhaust gas. The method provides for a tank mass flow supplied from the hydrogen reservoir to the anode circuit to be determined by balancing the material flows supplied to and discharged from the anode circuit, wherein the tank mass flow enters the balancing as a material flow supplied to the anode circuit.