What Is Fertility Rate?

The fertility rate is expressed as children per woman. So if all women have exactly 2.1 children, the fertility rate is 2.1. The replacement level is 2.1; that is, women need to replace themselves and one man, so that the population stays stable without additional immigration.

The replacement level has been about 2 for most of history, but for two hundred years it has been below 2 in most Western countries, and during that time the populations have not declined significantly.

Fertility rate is a term used by demographers to refer to the average number of children born per woman. Demographers tend to prefer this term to “population growth,” which is often used by lay people, because it does not assume that everyone in the population is fertile. In countries with high birth rates, there are always some people who have no children; in countries with low birth rates, there are always some people who have five. “Fertility rate” reflects the fact that most people fall somewhere in between.

The term “crude birth rate” is also sometimes used, but “fertility rate” has become standard among demographers and seems likely to stick.

The average fertility rate in Europe and the United States is now about 1.6 children per woman—which means that each generation is about half the size of its mother’s. At this rate, Europe will be extinct in fewer than eight centuries. This fact has produced a lot of hand-wringing. But why?

For one thing, the fertility rate is actually closer to 1.4. In France, for example, it’s 1.9; in Germany, it’s 1.4; and in Italy it’s 1.3—all below replacement level, but still well above zero. (Though still too low to mean that current populations are reproducing themselves.) For another thing, much of the decline from 2.1 children per woman in 1960 is not due to women having fewer babies but to fewer women having any babies at all—or ever again: In most European countries more women are childless now than ever before.