What an ageing population is and why it happens
An ageing population = a rising share of elderly people, caused by a low birth rate plus rising life expectancy.
An ageing population is one in which the proportion of older people (usually those aged 65 and over) is rising over time. It is about the balance of age groups, not just the total number of people.
Two demographic changes cause it (linking back to 3.1):
- a low (and often falling) birth rate — so fewer children and young adults enter the population at the bottom, and
- a rising life expectancy — better health care, nutrition, sanitation and safer work mean people live longer, so more people survive into old age.
Together these shift the population structure: the base of the population pyramid narrows while the top broadens. The share of working-age people (15-64) shrinks relative to the elderly, so the old-age dependency ratio rises.
| Old-age dependency ratio | Meaning |
|---|---|
| Low (e.g. 20) | About 20 elderly people per 100 workers — a light burden |
| High (e.g. 50+) | 50+ elderly people per 100 workers — a heavy burden on each worker |
Why it matters. When the working-age share falls and the elderly share rises, a smaller workforce must support a larger number of retired dependants — through the taxes they pay, the pensions that are funded, and the health and care services that are used. That single shift is the root of every impact in this subtopic.
- Ageing population = rising proportion of people aged 65+.
- Cause 1: low / falling birth rate (fewer young people at the base).
- Cause 2: rising life expectancy (more people survive into old age).
- The old-age dependency ratio rises as the working-age share falls.
- Result: a smaller workforce must support more retired dependants.