The calculations you have done always assume that you invest 20% of your initial invested amount every year. So it seems easy to double 5000 by adding another 1000 bucks "The saving of Rs 1,000 every year will cause no dent whatsoever in your lifestyle" but if I want to double Rs.50,000. The saving of Rs.10,000 may cause a dent in my lifestyle. I have nothing wrong against regular savings but the returns may not be as attractive as they look from your calculations.
