This study showcases a novel insight into the growth rate of Bangladeshi, Indian, and Nepali people, focusing on historical population patterns, contemporary demographic trends, and future population projections. Asia, home to over 4.5 billion people, accounts for approximately 70% of the global population, with Bangladesh, India, and Nepal being the most populous countries in South Asia. To facilitate chances for more significant policymaking in these nations, this study will examine the growth rate and its effects in the years to come. The demographic shifts in Bangladesh are creating new economic opportunities, with insights that can guide policymakers in refining population strategies, which are also relevant to India and Nepal. This study thoroughly assesses the precision and relevance of five mathematical models, e.g., the least squares model, Malthusian (exponential growth) model, logistic growth model, hyperbolic growth model, and discrete logistic growth model, in forecasting demographic changes in Bangladesh, India, and Nepal from 1950 to 2100. Furthermore, the study offers a speculative analysis of how these countries have previously handled population growth and the strategies they may adopt in the future.