Population Pyramids for Demographic Transition Stages 1 to 5

A population pyramid shows how many people are in each age band, usually split by sex. Its width at the bottom tracks recent birth rates, and its narrowing as you go up tracks deaths. So each stage of the demographic transition has a recognizable shape: a steep triangle, a wide-based triangle, a bell, a column, and a top-heavy column.

Shape by stage

• Stage 1 (high birth rate, high death rate): a steep triangle with a very wide base. Many babies are born, but many people die at every age, so the sides slope inward fast.
• Stage 2 (high birth rate, falling death rate): a wide base with a broader middle. Fewer children and adults die, so more survive into each age band. The population grows fast.
• Stage 3 (falling birth rate, low death rate): the base stops widening and starts to narrow. The pyramid looks like a bell or a rounded shape. Growth slows.
• Stage 4 (low birth rate, low death rate): a column with roughly equal widths across ages, narrowing only at the oldest ages. Growth is near zero.
• Stage 5 (birth rate below death rate, where the model includes it): an inverted or top-heavy shape, with a base narrower than the middle. The population shrinks without migration.

Stage 5 is not in every version of the model, so check which version the passage uses. Use the passage's stage definitions if they differ from your notes.

How to read any pyramid

1. Look at the base. A wide base means a high recent birth rate. A narrow base means a low one.
2. Look at the slope of the sides. Steep inward slopes mean high mortality. Straight sides mean most people survive to old age.
3. Look for dents. A notch in one cohort points to a war, famine, epidemic, or a short-lived drop in births. It travels upward as that cohort ages.
4. Compare the sexes. A longer female side at the top reflects higher female life expectancy in most populations.
5. Check the dependency ratio. A wide base means many young dependents. A wide top means many elderly dependents.

Momentum

A population can keep growing for decades after birth rates fall, because a large young cohort is still moving into childbearing ages. This is population momentum. It is why a Stage 3 pyramid with a bulge in the middle still grows even though each woman has fewer children.

Common traps

• Mixing up the base and the top. The base is births; the top is survival into old age.
• Calling a wide base "high population." It shows a high share of children, not a large total.
• Assuming Stage 4 means no growth. It means growth near zero, and some countries still grow through immigration.
• Forgetting that the pyramid is a snapshot. Cohorts shift upward each year.

One-minute recap

• Stage 1: steep triangle. Stage 2: wide-based triangle. Stage 3: bell. Stage 4: column. Stage 5: top-heavy.
• Base width tracks births; side slope tracks deaths.
• Momentum keeps growth going after birth rates fall.