A method for determining the instantaneous fluid level of a tank includes the steps of: designating a beginning fluid-level of the tank as an input value during the starting of the engine; ascertaining a first fluid-level value from a fluid level measured by a fluid-level measuring device, and ascertaining a second fluid-level value and a window around the second fluid-level value from the consumption of the engine and from the input value; comparing the first fluid-level value to the window around the second fluid-level value; determining whether the first or the second fluid-level value should be a new input value; displaying the new input value as the fluid level; and terminating the method if the engine is switched off or repeating the method starting from the ascertaining step when the engine is running.