To provide optimized real-time charging for simultaneous services there is provided a method and apparatus for executing a real-time charging session in a charging system being interfaced to at least one communication network. At start of a charging session or during re-authorization of reserved funds there is executed an optimized fund reservation for multi-service and/or multi-unit type services such that it is possible to optimize the fund resources considering various services and related service types in parallel. Fund reservation is executed for multi-service and/or multi-unit type services such that deviations between time of predicted fund depletion for the at least two services and/or for the at least two service types are minimized. Therefore, the signalling traffic to and from the charging system is reduced significantly.