A population pyramid shows who might be working and who might need support. The dependency ratio puts that into one number, using percents of a number.
Key idea
Dependency ratio = (people aged 0–14 + people aged 65 and over) ÷ people aged 15–64 × 100. It is the number of dependents for every 100 people of working age.
Why it works
Children under 15 are mostly in school, and many people over 65 have retired. Their food, schooling, health care and pensions are paid for largely by people of working age, through families and taxes. The ratio is only a rough guide: many teenagers and older people work, and many adults do not.
Worked examples
Worked example: From percents
A country is 38% under 15, 3% over 64, and 59% aged 15 to 64. Find the dependency ratio.
- Dependents: 38 + 3 = 41.
- Working age: 59.
- 41 ÷ 59 × 100 ≈ 69.5.
Answer: About 69 dependents per 100 people of working age.
Worked example: Young and old
Country A: 15% under 15, 25% over 64. Country B: 35% under 15, 5% over 64. Compare their dependency ratios.
- Both have 40% dependents and 60% working age.
- Both ratios: 40 ÷ 60 × 100 ≈ 66.7.
- But A's dependents are mostly old (pensions, health care) and B's are mostly young (schools).
Answer: Equal ratios (about 67), with very different needs.
Worked example: From counts
A town has 1,800 children under 15, 1,200 people over 64 and 6,000 people aged 15 to 64. Find the ratio.
- Dependents: 1,800 + 1,200 = 3,000.
- 3,000 ÷ 6,000 × 100 = 50.
Answer: 50.
Common mistake
Students count only the elderly as dependents. Children under 15 count too, so countries with many children (expanding pyramids) often have high dependency ratios, just like aging countries. Also, the ratio divides by the working-age group, not by the whole population. Check: if the answer is "percent of the population," you divided by the wrong number.