Hydraulic hardening of calcium aluminate cement (CAC) is primarily due to the hydration of mono-calciumaluminate, in idealized pure form CaAl2O4 (CA), but other compounds also participate in the hydration process especially at higher temperatures and in long term development. In this paper the early age hydration of synthetic CA and commercial iron-rich CAC were investigated by measurements of chemical shrinkage evolution and quantitative powder X-ray diffraction (QXRD) analysis. The influence of age of prepared CA was investigated. A simplified model is proposed to predict the evolution of chemical shrinkage during early age of the hydration. The model is based on the main chemical reaction scheme of the CA hydration at lower temperatures.