replacementlevel

Replacement level fertility is the total fertility rate at which a population exactly replaces itself from one generation to the next, assuming current mortality and sex ratios at birth and no net migration. It serves as a benchmark for demographic stability, indicating whether population size would remain steady over time if other factors stayed the same.

In practice, replacement level is not a single universal number. In many developed countries, it is about 2.1 children per woman, reflecting low child mortality and balanced sex ratios. In countries with higher infant mortality or different sex ratios, the replacement level can be higher, often around 2.3 to 2.5 or more. The exact value depends on mortality conditions and the proportion of births that survive to reproductive age.

The relationship between replacement level and population growth depends on migration. If the total fertility rate stays above replacement level and net migration is small, the population tends to grow. If fertility falls below replacement and migration is limited, the population tends to decline. Migration can offset a low birth rate, sustaining population size or altering age structure.

Replacement level is a demographic concept used for projections and policy planning, not a fixed policy target. It is influenced by factors such as health care, education, economic development, and access to family planning. Limitations include its reliance on current mortality and migration assumptions and its neglect of age structure and future social changes. Despite these caveats, it remains a core metric in understanding long-term population dynamics.