Johan Strålfors presents his master's thesis Calibration of a dynamically weighted Heston and Levy model using the iterated extended Kalman filter Abstract A wide set of financial derivatives is in use today, almost none of the more complex have readily available two way price quotes. To price these we need to determine a suitable model for the price process of the underlying asset. This thesis proposes a dynamically weighted mix between the finite moment log stable and Heston models, calibrated to daily option data with the iterated extended Kalman filter. The data used is a set of vanilla option prices from the S&P 500. The mixed model outperforms both the Heston and finite moment log stable process in terms of absolute price deviations and inside spread predictions but the estimated parameters show less stability in simulation studies.