The main objective of this paper is to examine age structure changes of the population and determine the timing of the demographic dividends in Sri Lanka. The study confirms that the duration of the first demographic dividend is 45 years from 1992 to 2037. This suggests that Sri Lanka is still left with 21 years more, which is a considerable time period, if the country desires to benefit from this historically produced demographic bonus. The benefits of the demographic dividend which are available only for about another two and half decades are not automatic, but policy dependent and hence, the window of opportunity to reap the benefits of a low dependency burden needs to be made use of productively. The study also shows that the second demographic dividend will commence from 2037 in Sri Lanka. It is expected that the second dividend comes into operation in part because prime age adults save more to provide for their retirement. Their ability or willingness to save, nevertheless, may be undermined by poorly developed financial markets or overly generous publicly funded pension programmes. These suggest that the changes in age structure define possibilities, but by themselves, do not decide the outcome. [ABSTRACT FROM AUTHOR]