Fertility rate
Total fertility rate: the average number of children a woman would bear at current age-specific birth rates.
How it is measured
From birth registration and survey data, standardized by the UN Population Division.
Where the number came from
Total fertility rate is a synthetic construct rather than an observation: it sums this year’s birth rates at every age into an imaginary woman who lives through all of them at once. Demographers adopted it because the alternative, waiting for a real cohort to finish childbearing, takes about thirty-five years to produce an answer. The cost of that speed is a well-documented distortion first formalised by John Bongaarts and Griffith Feeney in 1998: if women across a society start having children later, the period rate falls even when nobody ends up with a smaller family, because births are pushed out of the observation window rather than out of existence. When the postponement stops, the rate partly rebounds. This "tempo effect" is why a very low reading in a country where the average age at first birth is still rising should be read with caution, and why demographers watch completed cohort fertility alongside it.
Worked example: South Korea at 0.75 and Niger at 5.79
Our 2025 figures put South Korea at roughly 0.75 children per woman, the lowest reading for any sizeable population ever recorded, against Niger at about 5.79 and Chad slightly higher. France sits near 1.64 and Japan near 1.23. Replacement level, the rate at which a population reproduces itself without migration, is about 2.1 in a low-mortality country and higher where child mortality is significant, so most of Europe and East Asia is well below it and much of the Sahel is far above. What makes South Korea genuinely remarkable rather than merely low is that 0.75 is under half of replacement, which compounds brutally: absent migration, each generation would be a little over a third the size of the one before. Some of that reading is tempo, since Korean women continue to have first births later, and the completed family size of Korean cohorts will end up somewhat above 0.75. But not remotely enough to close the gap to 2.1. Contrast the arithmetic in Niger, where a rate near 5.79 combined with falling child mortality is why its median age is about 15.6 and its population growth near 3.2 percent a year: fertility is the input, and age structure and growth are what it produces a generation later.
Figures read from our own fertility rate table; each row there carries its observation year and whether it came from a live feed or the frozen archive.
Our data source
UN World Population Prospects 2024, medium variant.
Refresh cadence: Biennial UN revisions.
What to watch for
Replacement level is about 2.1 in low-mortality countries. A period measure that can be distorted when women delay births: the rate dips even if completed family size does not.
CIA World Factbook equivalent field: "Total fertility rate" (frozen at the January 2026 final edition; our figures continue from live sources).