The accuracy of the kinetic parameters determined by TG or DTA/DSC is evaluated through the calculation of simulated {W, Tp} curves. The already proposed method of simultaneous refining of thermal and kinetic parameters is much more accurate than commonly used methods. The reaction enthalpy, thermal capacity and heat transfer, are discussed with respect to parameter accuracy, as well as to noise and discrete sampling and to temperature inaccuracy. The errors are evaluated and some suggestions are derived to improve the reliability of experiments.