Demographic Shifts: Aging & the Population Pyramid

Population Model

Fertility rate (TFR) 2.1

Life expectancy 75 yrs

Simulation speed 3 yrs/s

Year

–

Total population

–

Median age

–

Dependency ratio

–

Growth rate

–

65+ share

–

How it works

Every year the model advances one full population cohort: each single-year age band survives forward at a rate set by the life-expectancy slider (mortality rises steeply above roughly that age, following a Gompertz-style curve), while new births are added at the base of the pyramid in proportion to the fertility rate (TFR) and the number of women currently aged 15–49. Bars extend left for men, right for women; height is age, thickness is cohort size — the classic population pyramid, rendered as a real 3D stack you can orbit.

survivors(age+1) = alive(age) · (1 − q(age, lifeExpectancy))
births = (TFR / 35) · Σ women aged 15–49
dependency ratio = (age<15 + age≥65) / age 15–64 × 100

Fertility rate (TFR) — average children per woman over a reproductive lifetime. ≈2.1 holds a population roughly level; South Korea sits near 0.72, Niger above 6.
Life expectancy — shifts the whole mortality curve; a higher value lets far more cohorts survive into old age, widening the top of the pyramid over decades.
Simulation speed — years advanced per second, so you can watch a full demographic transition play out in under a minute.

Run "Youthful" and it keeps its broad-based, triangular shape — a growing population like Nigeria's. Run "Aging" for a while and the base narrows while the top swells — Japan's and South Korea's trajectory, where a shrinking working-age base has to support a growing retired one.

2024

Men Women Working age 15–64

⚠ Couldn't load the 3D engineThree.js failed to load from the CDN. Check your connection and reload.