This study reports the prediction of ultimate mortar expansion (UME) due to alkali-silica reactivity. The investigated sixteen aggregate groups with a wide range of geology and mortar expansion that were utilized in this study were obtained from two existing experimental studies. The expansions over the 28-day testing period were fitted with the ASR decay model to predict the UME and time required to reach 50%, 75%, 90% and 95% of UME. The study showed that the ultimate mortar expansion varied with aggregate mineralogy. Finally, aggregates susceptible to alkali-silica reactivity were determined based on the proposed limit of ultimate mortar expansion, and they were compared with the results obtained by the aggregate geology and expansion limits at test durations of 14 and 28 days.