The calculation of thermal endurance and the estimation of lifetime at certain temperatures based on thermogravimetric data for the tungstophosphoric acid, H3[PW12O40]·H2O (H3PW) and its Cs acidic salts, pure or doped with Pd, were done. The calculation of catalyst’s lifetime with high degree of confidence needs reliable values for activation energy. For this reason, the activation energy values were calculated with ASTM E 1641-04 “Standard Test Method for Decomposition Kinetics by Thermogravimetry” based on Flynn–Wall isoconversional method and with Friedman isoconversional method (differential model-free) for checking, because the last provides accurate values of activation energies compared with the integral model-free methods. The thermal decomposition of the H3PW and some of its acidic Cs salts, pure or doped with Pd, occurs through the constitutional water release [the water formed of the protons and the oxygen from the [PW12O40]3−] having as result the loss of acid sites (protons) and its catalytic activity diminution at the same time. The activation energies are reliable values for the conversion range of 5 ≤ α ≤ 20, but the value for α = 10 % is recommended for the calculation of the lifetime. The estimation of lifetimes was done with ASTM E 1877-00 “Standard Practice for Calculating Thermal Endurance of Materials from Thermogravimetric Data” method. The estimated thermal life of the H3PW and some of its acidic Cs salts pointed out a very good thermal endurance at temperatures below 573 K. The Pd doping decreases drastically the thermal endurance in all cases.