Geopolymers are cement-free constructional materials and for their production much lower greenhouse gases are emitted than traditional concrete. In this study, compressive strength of geopolymers was related to their degree of geopolymeric reactions. Then, the Johnson-Mehl-Avrami-Kolmogorov equation was applied to represent compressive strength evolution. The presented equation can be easily adopted for prediction of long-term compressive strength of geopolymers and even traditional cementitious systems. Johnson- Mehl-Avrami-Kolmogorov constants were shown to be higher for specimens with higher strengths while their corresponding exponents were smaller.