Population pyramid

A population pyramid is a chart showing the distribution of a population by age group and sex, typically drawn as two horizontal bar charts back to back, one for each sex, stacked by age band from youngest at the bottom to oldest at the top.

The overall shape communicates demographic trends at a glance: a wide base that narrows steadily toward the top ("expansive") indicates high fertility rates and a young, growing population; a shape with a narrow base and bulging middle ("constrictive") indicates falling fertility and an aging population; and a roughly even-width shape ("stationary") indicates a population near replacement level with slow or no growth. Migration can distort the expected shape at specific ages, which is why analysts often check migration flows data before reading age-structure changes as purely a fertility or mortality story.

Population pyramids are used alongside the dependency ratio to assess the economic pressure an age structure implies, since a constrictive pyramid signals a rising share of older dependents relative to the working-age population, and alongside life expectancy trends to understand how a population is aging. A common pitfall is reading a single year's pyramid as a prediction rather than a snapshot: today's age structure constrains future population trends but does not fix them, since fertility, mortality, and migration can all still change.