The research is part of the advanced road map from the previous research. Identifying the problem studied is the user's assessment of the application product being developed for the suitability of the problems found. The aim is to test and assess the validity and reliability of Act.Fit, is an Android-based application developed in previous research. The method developed is survey. The research steps were: 1) Formulating research problems and determining research objectives, 2) Setting the concepts and hypotheses and studying literature, 3) Sampling, 4) Making questionnaires and instruments, 5) Collecting field data, 6) Managing data, and 7) Analyzing and reporting. The research area was Yogyakarta. The research subjects were 30 adults. Online questionnaires were used to collect data on app-based BMI and physical fitness assessment. The statistical analysis used is descriptive. The instruments were valid and reliable, with mean scores of 0.632 and 0.651, respectively. The scores, accordingly, proved the instruments’ validity and reliability. User assessment of the application resulted in: 1) The appearance was scored at 4.66 with a Very Good category, 2) The material was scored at 4.52 with a Very Good category, 3) The learning aspect was scored at 4.49 with a Very Good category, and 4) The utility was scored at 4.56 with a Very Good category. In conclusion, the application developed by the researcher gets a Very Good feasibility score from the user. Based on that results, the researchers will continue research at the mass production stage.