Different methods for calculating the entropy change in the thermoelastic martensitic transformation were analysed. A new way of estimating the transformation entropy was proposed based on the simple relationship between the heat released during the forward martensitic transformation and the finish temperature of the forward phase transition. The value of the B2-B19' transformation entropy was calculated for Ti50Ni50 alloy using the different methods. It was shown that the values of entropy change calculated based on the “entropy argument”, “Clausius–Clapeyron relation” and through the calorimetric data (proposed in the present work) were close to each other and gave values which were approximately equal to 0.105 J/(g K). As the method proposed in the present work is simpler than others, it might successfully be used to estimate the transformation entropy and the contributions of the latent heat, elastic and dissipative energies.