Pavement management system (PMS) has been considered as an essential tool for proper allocation of maintenance funds by monitoring pavement health. Research related to PMS can be found across the world, especially for flexible pavements, but very few researches have been conducted in Bangladesh, where pavements are mostly flexible. Roads in Bangladesh are being constructed for a design life of 20 years provided that a resurfacing treatment is given after 10 years since initial construction, but due to lack of proper maintenance of pavements, the life span plunges to around 5 years. Deflection is recognized by pavement researchers as a vital parameter to evaluate the structural strength of pavements. In comparison with measuring deflection, International Roughness Index (IRI) is easier and less costly to measure on the field. This research aims at developing an empirical model to predict the deflection of flexible pavements using IRI values based on practical data of flexible pavements of varying ages. Following a reconnaissance survey, road sections corresponding to different road classifications constructed and maintained by the Roads and Highways Department (RHD) have been selected for conducting the analyses. Pavement deflection, IRI data, road width, average annual daily traffic (AADT), and time since the last overlay on selected flexible pavement sections have been collected from the database of Road Maintenance Management System (RMMS) of RHD, Bangladesh. The developed empirical linear regression model explains the relationship between deflection and IRI values of flexible pavements with varying pavement age capable of explaining 61.8% variance of the outcome variable. Both IRI and age have been found to be positively correlated with deflection. The outcome of this research work will help in improving the pavement management system in Bangladesh by using IRI values to predict the deflection of pavements and take adequate rehabilitation measures at regular intervals.