The present study is an attempt to explore the causes and consequences of population aging in Bangladesh. The current situation and future trend of population aging under the changing condition of demographic variables, specifically, fertility and mortality. The studies have analyzed the demographic transition caused by reduction in fertility and mortality and also identify the factors affecting the aged population. To estimate and project the aged population, the models viz. Exponential growth model, Modified exponential growth model, Geometric model, Makeham’s model and Logistic model have been used. The study has estimated and projected mid-year female population of Bangladesh by age group during 1991-2021 and through applying Frejka’s component method in Leslie matrix form. Finally, Cohort component method has been used to estimate and project the mid-year total population of Bangladesh by age group. Estimate and projection of the aged population reveal that in next 20 years their number is expected to increase nearly 205 times than today. The aged population of Bangladesh will increase gradually up to 2021 and thereafter it will increase remarkably.