As a consequence of the increasing share of renewable energy sources in present-day electrical grid systems, time variations of the power demand for fossil fuel plants can become more sudden. Therefore, an ability to respond to sudden load changes becomes an important issue for power generation gas turbines. This paper describes a real-time model for predicting the transient performance of gas turbines. The method includes basic transient phenomena, such as volume packing and the heat transfer between the working fluid and the structural elements. The dynamics of components are quantified by solving ordinary differential equations with appropriate initial and boundary conditions. Compressor and turbine operating points are determined from corresponding performance maps previously calculated using sophisticated aerodynamic, through-flow codes. This includes a sufficient number of such characteristics to account for the variations in speed and machine geometry. The developed dynamic model was verified by comparison of simulation results with experimentally recorded operating parameters for a real engine. This includes the start-up sequence and the change of load. Additional simulation covers the system response to a step increase in fuel flow. The simulation is carried out faster than the real process.