As a result of the worldwide energy transition, reactive power generation has started to become a more scarce resource in the power grid. Until recently, reactive power has been an auxiliary grid service that classical power generation facilities have provided without necessarily allocating any cost for this valuable service. In this paper, a new approach for predicting the additional costs of reactive power services delivered by large hydrogenerators is proposed. We derive the optimal reactive power with minimal losses as a function of the active power level within the generator’s capability diagram. This pathway can then be used to calculate additional losses from operational regimes deviating from the optimal reactive power for each active power level. To back up the analysis, a dedicated population study was handpicked consisting of four real-world generators scaled in terms of power rating, i.e., 15 MVA, 47 MVA, 103 MVA, and 160 MVA. The objective was to identify how the optimal reactive power scale from smaller to larger MVA-sized generators. Moreover, a sensitivity analysis explores the link between the standard parameters, the stator losses, the rotor losses, the optimal reactive power, and the optimal efficiency. We find the ratio between the rotor and stator losses as the determining factor. Finally, the operational pathway introduces a new way to allocate the power producer’s cost associated with their reactive power services and can be used to justify potential profit for this service, especially considering that the intermittent reactive power needs are projected to increase in the future.