It is described a method of estimating additional power output for inertial response that will be available for output throughout a preset inertial response time interval, the method including: obtaining current values of at least a rotational speed of a wind turbine rotor and a power output of the wind turbine; deriving the additional power output based on the obtained current values and a remaining time interval of the preset inertial response time interval, in particular such that the additional power is available for output during the entire predetermined time interval.