"Demographic bonus" connotes the period when the dependency ratio in a population declines because of :-

"Demographic bonus" connotes the period when the dependency ratio in a population declines because of decline in feility, until it stas to rise again because of increasing longevity. "Demographic burden" is used to connote the increase in the total dependency ratio during any period of time, mostly caused by increased old age dependency ratio Dependency ratio = (Propoion of ppl in < 15yrs of age + >65yrs of age) / Propoion of ppl in 15-64 yrs of age