What is the replacement fertility rate?

• ≈2.1children per woman, approximately
• 129of 236 countries below it
• 67%of world population lives below it
• 45%of world births happen below it

Why 2.1 and not 2

Two children replace two parents, so the intuition says 2. Two corrections push it above that. The first is the sex ratio at birth: slightly more boys are born than girls (about 105 to 100), and it is the daughters who produce the next generation, so rather more than two children are needed to yield one daughter per mother. The second is mortality: some of those daughters do not survive to the end of their own childbearing years.

Put together, in a country with low child mortality the level works out at roughly 2.05 to 2.1, which is where the conventional 2.1 comes from. It is a rounded convention, not a measurement, because the exact figure differs by country and by decade. That is why this site writes "about 2.1" and uses it as one threshold rather than recomputing it per country from data it does not hold.

Where replacement level is higher

Where more girls die before adulthood, more have to be born for the generation to be replaced. In the countries with the highest child mortality the replacement level is meaningfully above 2.1, and estimates in the demographic literature run to around 2.5 and, historically, well beyond that.

This matters for reading any table of fertility rates, including the one on this site: a single 2.1 line drawn across every country is an approximation that is most accurate for the countries with the lowest mortality, which are also the countries furthest below it. The countries where the correction is largest are the ones comfortably above the line either way.

Below replacement does not mean shrinking

A population is a stock, and fertility is a rate acting on part of it. When fertility falls below replacement, the people who will be having children for the next twenty-five years have already been born, and if the generations before were large, the number of births stays high for a long time afterwards. Demographers call this population momentum, and it is why a country can be below replacement for decades while still growing.

The world as a whole shows it. Annual births peaked in 2012 at 146 million and have been falling since, yet on the UN's medium scenario world population goes on rising until about 2084, reaching 10.29 billion. Migration complicates it further at country level: it changes a population without changing its fertility at all.

How many countries are below replacement

In 2023, 129 of 236 countries and areas with a published fertility rate are below about 2.1. Those countries contain 67% of the world's population but account for 45% of its births. It is the clearest single illustration of what being below replacement does to a birth count.

Countries sitting within a tenth of a child of the line are worth looking at directly, because they are the ones a single year's movement can push across it, and because crossing it is a statistical event, not a demographic one. Nothing happens to a country on the day its fertility passes 2.1.

See fertility on the map

Read next

• Fertility rate by country
• Why fertility is dropping
• Lowest fertility rates
• Highest fertility rates
• Birth rate vs fertility rate
• How many babies are born each year?