Declining Fertility Rates across the World | St. Louis Fed

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Declining Fertility Rates across the World

June 09, 2026

By

B. Ravikumar

Guillaume Vandenbroucke

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KEY TAKEAWAYS

The total fertility rate (TFR), or the average number of births per woman over her entire reproductive life, is one factor affecting population growth. Trends in the TFR have implications for the world’s demography.

Although poor countries have a higher TFR than rich countries, the rate has been declining in both for 60 years. This has narrowed the TFR gap between the poorest and richest countries from three children per woman to less than one child per woman.

In rich countries, the TFR has been lower than the rate needed to maintain population levels for a few decades. But the TFR in low-income countries remains higher than the replacement rate.

According to the last U.S. census in 2020, the population growth in the U.S. was the lowest since the Great Depression. Lower population growth is not unique to the U.S.; it is a global phenomenon. (See, for example, this Council on Foreign Relations article.)

In simple accounting terms, population growth is the result of changes in births, deaths and net migration. The focus of this blog post is on births, more specifically the total fertility rate (TFR), across countries. TFR is the average number of births per woman over her entire “reproductive life” (typically, ages 15 to 49). For every year, it is computed by summing the age-specific birth rates (number of births per woman in a specific age group) in that year for women in their reproductive phase of life.

Total Fertility Rate and Crude Birth Rate: An Example

While the crude birth rate enters directly into the calculation of the population growth rate, the TFR does not. However, the TFR affects the population growth rate via its relationship with the crude birth rate. The example below illustrates the relationship.

The crude birth rate in a year is the ratio of the number of births in that year to the population in that year. Suppose, for example, this ratio is 0.02, i.e., the number of births is 2% of the population. Suppose women constitute one half of the population. Then, births per woman must equal 0.02 x 2 = 0.04. Suppose 50% of the women in the population are in their child-bearing years. Then, births per child-bearing woman is 0.04 x 2 = 0.08. Suppose that the span of child-bearing years is 35 (e.g., ages 15 to 49). Then, births per woman over her entire reproductive life—i.e., TFR—must equal 0.08 x 35 = 2.8.

In computing the TFR, this example makes several assumptions: The sex ratio (ratio of males to females in the population) is 1, the mortality rate for women is zero during the child-bearing years, the birth rate is the same in every child-bearing year, etc. For instance, if women were less than one half of the population, say only 45%, then TFR would increase to 3.1.

Total Fertility Rate in Poor and Rich Countries

The figure below illustrates the TFR in poor and rich countries. We rank countries in the increasing order of their real gross domestic product (GDP) per capita in 1960. Then, we combine them into five groups, or quintiles, with each quintile having almost the same number of countries. (We excluded China from our sample since their one-child policy, which was in force during most of the years in our sample, might affect our calculations on cross-country differences in TFR.) The figure plots the TFR in the poorest and richest quintiles.

In general, there is a negative relationship between TFR and GDP per capita: Poor countries have higher TFR than rich countries. However, the TFR has been declining in both poor and rich countries for the past 60 years. In 1960, the difference in TFR between the poorest and richest quintiles was approximately three children per woman over her entire reproductive life, but this difference had declined to less than one child by 2023.

Total Fertility Rate Needed to Maintain Population

While rich countries’ TFR has been below the “replacement rate” for a few decades, the TFR in poor countries remains above the replacement rate. What is the replacement rate? It is the value of TFR such that the population remains at a constant level (population growth rate is zero), holding all other determinants of population constant.

A good guess to maintain a constant population would be a TFR of 2.0. However, as we noted earlier, a higher ratio of males to females in the population increases the TFR needed to maintain the population level. Accounting for the observed sex ratio, mortality, etc., would increase the replacement rate to a value above 2. Empirically, the typical value is 2.1.

Conclusion

To summarize, the TFR has been declining for several decades in both poor and rich countries. Lower values of TFR imply lower population growth. Unlike for rich countries, poor countries’ TFR is above...