OBJECTIVE To ascertain the relationship between dental age and chronological age in patients attending dental OPDs using third molar calcification stages. METHODS A cross-sectional analytical study. METHODS Dental OPDs of Dow University of Health Sciences, Karachi, Pakistan, from November 2021 to April 2022. METHODS Dental Orthopantomograms (OPG) of 385 patients, aged 12-28 years attending the dental OPDs, were obtained during the study period. Third molar calcification stages were evaluated using the method proposed by Kohler et al. based on ten stages of tooth formation. The inter-examiner agreement was tested by adding another examiner to 100 dental OPGs after 30 days of reviewing them by one examiner. A simple linear regression model was applied between age and stage of tooth growth. RESULTS A total of 121 males (31.4%) and 264 (68.6%) females were included in this study. Intra-agreement and inter-agreement were excellent (˃0.90). A total of 55 (14.28%) had half of the root completed, followed by 49 (12.72%) who had initiation of root formation and 1/3rd root completion. The left mandibular third molars were found to be more statistically significant with Kohler's stages of development in both genders. CONCLUSIONS Developing third molars was significantly related to chronological age and provided the most accurate age calculation based on all tooth measurements and ratios of tooth measurements. Third molar calcification stages can be used accurately to predict age in Pakistani adolescents. BACKGROUND Dental age estimation, Chronological age, Dental radiographs, Orthopantomograph, Third molar development.