Eurostat, WHO, OECD: The mean number of children that would be born alive to a woman during her lifetime if she were to pass through her childbearing years (conventionally 15-44, sometimes 15-49) conforming to the fertility rates by age of a given year. It is therefore the completed fertility of a hypothetical generation, computed by adding the fertility rates by age for women in a given year (the number of women at each age is assumed to be the same).
Total fertility rate (TFR) calculated as a period indicator (e.g. assuming that age-specific fertility levels remain constant in the future), not by birth cohorts. Completed fertility rate by birth cohort (CFR) refers to the average number of children at the end of reproductive period. TFR and CFR differ significantly if the timing of childbearing differs by time or by country.
Basic demographic data. Total fertility rate is also used to indicate the replacement level fertility, in more developed countries, a rate of about 2.1 can be considered to be replacement level.