In the present study, the operational lifetime of a solid oxide fuel (SOFC) short stack is predicted by investigating the performance degradation of both the short stack and its cells throughout 1000 h at 800 °C. The short stack and integral cell voltages are continuously measured during the long-term test, with electrochemical impedance spectroscopy (EIS) conducted every 200 h. The short stack voltage decreased rapidly for the initial 200–300 h and afterwards, it decreased at a slow rate due to the increase in the Ohmic and polarization resistances in the same manner. Scanning electron microscopy results show that there is no delamination or cracking among constituent layers of the short-stack cells. The single degradation effects of the Ni coarsening in the anode, cation migration and surface segregation in cathode and oxide scale growth in metallic interconnect mesh are successfully integrated into a comprehensive lifetime prediction model. The experimentally measured voltage degradation data of the short stack fits well with the developed mathematical model and allows the successful prediction of the lifetime up to 50,000 h.