In economics and geography the dependency ratio is an age-population ratio of those typically not in the labor force (the dependent part) and those typically in the labor force (the productive part).

Formula

In published international statistics, the dependent part usually includes those under the age of 15 and over the age of 64. The productive part makes up the population in between, ages 15 – 64. It is normally expressed as a percentage:

(Total)\ Dependency\ ratio = \frac{(number\ of\ people\ aged\ 0\ to\ 14\ and\ those\ aged\ 65\ and\ over)} {number\ of\ people\ aged\ 15\to \ 64} \times 100

As the ratio increases there may be an increased burden on the productive part of the population to maintain the upbringing and pensions of the economically dependent. This results in direct impacts on financial expenditures on things like social security, as well as many indirect consequences.

The (total) dependency ratio can be decomposed into the child dependency ratio and the aged dependency ratio:

Child\ dependency\ ratio = \frac{number\ of\ people\ aged\ 0-14} {number\ of\ people\ aged\ 15-64} \times 100

Aged\ dependency\ ratio\ = \frac{number\ of\ people\ aged\ 65\ and\ over} {number\ of\ people\ aged\ 15-64} \times 100

Inverse

The inverse of the dependency ratio, the inverse dependency ratio can be interpreted as how many independent workers have to provide for one dependent person (pension & expenditure on children)