Total fertility rate

Total fertility rate is the number of children a woman would have if she experienced the age-specific fertility rates observed during a particular period throughout her reproductive years.

Age-specific fertility rate: The number of births per woman or per 1,000 women in a specified age group during a given period. Total fertility rate sums these rates across reproductive ages.
Demographic transition: The historical shift from high birth and death rates to low birth and death rates as societies change. Falling total fertility rate is a central feature of many transitions.
Gross reproduction rate: The average number of daughters a woman would bear under current age-specific fertility rates, ignoring female mortality. It counts daughters rather than children of all sexes.
Sub-replacement fertility: A fertility level below that required for a population to replace itself across generations without migration. It describes total fertility rates below the replacement benchmark.
Period fertility measure: A demographic measure calculated from events observed during a defined time period rather than across an actual cohort’s lifetime. Total fertility rate describes a hypothetical lifetime based on one period’s rates.
Population projection: A calculation of future population size and composition based on assumptions about fertility, mortality, and migration. Total fertility rate informs fertility assumptions in projections.
Net reproduction rate: The average number of daughters a newborn girl would bear under current fertility and mortality rates. It incorporates female survival, unlike total fertility rate.
Population aging: An increase in the share of older people in a population, often accompanied by a rising median age. Persistently low fertility can contribute to population aging over time.
Cohort fertility: The number of children actually born to members of a birth cohort over their reproductive lives. Unlike total fertility rate, it follows real women through time.
Population momentum: Continued population growth after fertility falls to replacement level or below, caused by a young age structure. It explains why low total fertility rate does not immediately cause population decline.

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