The total fertility rate in the United States has been in decline since the start of the Great Recession. Since then, the total fertility rate has fallen far below the replacement level—the level of fertility necessary for the current generation to replace itself.REF If sub-replacement fertility is sustained for a long period of time, a population can eventually contract if there is not enough positive net migration to account for sub-replacement births.

Much of the recent decline in fertility is a result of women increasingly postponing births. A variety of causes contribute to the increasing postponement of fertility, but among the most important contributing factors is the fact that men and women in the U.S. have been increasingly delaying marriage. The delay in marriage has reduced the window of opportunity that women have to decide to have children with a stable and reliable partner.

Some of the recent decline in fertility may be recaptured as cohorts age. But if fertility intentions are not realized in time, postponed fertility becomes forgone fertility. As marriage and childbearing continue to happen later in life, it is likely that more postponed fertility will become forgone fertility.

Charts 1–9 showcase some of the effects that marriage, age, the postponement of fertility, and the age structure of the population have on the fertility rate in the United States.

Women in the U.S. Are Increasingly Delaying Childbearing

Over the past 50 years, women in the U.S. have gradually delayed fertility. While in the early 1970s, most births were to women in their early to late twenties, by 2023, the majority of births were to women in their late twenties and early thirties. Since 1970, fertility rates for women 15 to 29 years of age have plummeted, while fertility for women in their thirties and early forties has increased markedly.

Chart 1 shows the age-specific fertility rates of U.S. women by five-year age group. The age-specific fertility rate is the number of births per 1,000 women in each age group.

Fertility among women 20 to 24 years of age has dropped the most. In 1970, women 20 to 24 years of age had an age-specific fertility rate of 167.8 births per 1,000 women. By 2023, that rate had dropped to 55.4 births per 1,000 women. In 1970, women 20 to 24 had the highest fertility rate of any age group. By 2023, it had fallen below that of women 25 to 29 and 30 to 34 and has nearly crossed with that of women 35 to 39.

Meanwhile, fertility for women in the 30-to-34 and 35-to-39 age groups has increased considerably. Women in their early thirties now have the highest fertility rate of any age group. The age-specific fertility rate for women 30 to 34 years of age has now nearly replaced the fertility that women in their early twenties had in 1975. The rise in fertility among women 35 to 39 has also nearly replaced the fertility rate that girls 15 to 19 had in 1975. Despite the dramatic increases, however, the gains in fertility rates among women in their thirties and forties have not been enough to counterbalance losses in fertility among women under 30.

Fertility by Marital Status

Fertility in the United States is considerably higher for married women than for unmarried women.

Chart 2 shows the birth rates for married and unmarried women. The birth rate here is defined as the number of births per 1,000 women 15 to 44 years of age. It is the rate at which births occur in a given year relative to the population of reproductive-age women.

Birth rates for married women were on the rise until 2016 but have been declining since at least 2018. The dip in married fertility in 2017 is potentially misleading because California stopped reporting the marital status of birth mothers in 2017.

Birth rates for unmarried women were in decline from 2008 to 2016, and for states excluding California, from 2017 to 2023.

The Rise of Unwed Childbearing Has Plateaued in Recent Years

The share of births to unwed mothers rose steeply between 2003 and 2009 but has since plateaued. Chart 3 shows the percentage of all births to unwed mothers. Data after 2016 exclude the state of California.

By 2023, 40 percent of all births in the U.S. (excluding California) were to unwed mothers. The majority of births were still to married mothers, but the share of married births is much smaller than it used to be.

Americans Are Increasingly Delaying Marriage

Both men and women in the United States have been gradually delaying marriage since the 1960s. Chart 4 shows the estimated median age at first marriage by sex in the U.S.

In 1960, the median age at first marriage was estimated to be 20.3 for women and 22.8 for men. By 2023, the median age at first marriage had increased for women by 8.1 years and for men by 7.4 years.

This gradual delaying of marriage accounts for some of the increasing delay in childbearing over the past 50 years. For women, delaying marriage means fewer reproductive years spent within marriage. Women in the U.S. are much more likely to have a child when they are married than when they are not married. More delay in marriage results in fewer years of exposure to the higher fertility rates within marriage. It narrows the window of opportunity that women have to have children with a steady and reliable partner.

Birth Rates Among Married Women by Age

The delay in childbearing has much to do with the postponement of marriage. But even within marriage, Americans are postponing having children.

Chart 5 shows birth rates for married women, disaggregated by age group. This shows the rate at which married women have children at each age.

In short, many of the same trends in fertility occurring in the population at large are also occurring among married women, simply on a less drastic scale. Fertility for married women 20 to 24 years of age has declined since 2004. Meanwhile, fertility has increased for married women in their thirties and early forties. Between 2004 and 2016, age-specific marital birth rates increased for women over 25. However, since 2017, birth rates in the U.S. (excluding California) decreased slightly for women 25 to 29 years of age and for women between 30 and 34.

Marriage Is Declining Across All Ages Groups

The percentage of women who are married during their childbearing years has declined considerably. Chart 6 shows the percentage of women between 20 and 44 who are married over time. In 2004, 57.3 percent of women 20–44 years of age were married. By 2023, this percentage had plummeted to 45.7 percent.

Chart 7 breaks this down by age group. Since 2004, marriage has declined across all age groups. The steepest declines have been among women between 20 and 35—women who are in their prime childbearing years.

Unlike fertility (see Chart 1), the share of women who are married is not increasing for any age group. Over time, age-specific fertility rates have increased for women over age 30—an indication of a delay in fertility. But for marriage, there is no age group where the share of women married is increasing. Consequently, women are not just delaying marriage, many appear to be forgoing marriage entirely, or at least postponing it beyond the age when they can have children.

While a high percentage of women are still getting married by their late thirties, the percentage is not as high as it used to be. As is apparent from Chart 1, fertility rates for women over 35 so far have not been high enough to make up for the decline in fertility among younger women. The total fertility rate in the U.S. is unlikely to rise to the replacement level if marriage does not return to previous levels among women in their prime childbearing years.

The Age Structure of the Population Is Ripe for a Baby Boom, But Births Have Not Increased

The age structure of the population can have a sizable effect on the number of births that occur in a given year. If there are more women in their prime childbearing years, the number of births will go up even if fertility rates remain constant, simply because there are more women in age groups with high fertility rates.

Chart 8 shows the population of U.S. women under 40 by five-year age groups, and Chart 9 shows the annual number of births in the United States. Between 2016 and 2019, the U.S. saw its largest cohort of women ever enter their late twenties. Since fertility rates for women between 25 and 29 years of age are higher than that of any other age group aside from women between 30 and 34, one would generally expect to see the number of births rise during these years if all other age-specific fertility rates are held constant.

But instead of rising, births fell as fertility rates for the 25-to-29 age group dipped. Even with a small dip in fertility, the number of births may have risen, but the age-specific fertility rates collectively just fell too far.

This same cohort is now in its early thirties, which is currently the age at which women have the highest fertility rate. And considering the fact that the biological capacity for having children tends to decline rapidly after age 35, this large cohort does not have much more time to delay childbearing if childbearing is in their plans. As a result, the time is ripe for a mini baby boom, but a rise in births has not materialized. Time will tell if births have simply been postponed. But it appears they may be forgone altogether.

Chart 8 shows that this sustained drop in fertility resulted in far fewer girls up to four years of age since 2019. In fact, the current zero-to-four-year-old cohort is the smallest such cohort since 2004. This will, in turn, have downstream effects on the number of births 20 to 30 years from now when females in this group enters their childbearing years. One can expect far fewer births from this cohort owing to its relatively small size.

Policy Considerations

Women in the U.S. are delaying both childbearing and marriage. Both factors are contributing to the decline in fertility. Public policies that aim to help to women attain the number of children they want to have should support women in getting married before they are no longer able to attain their desired number of children.

Men and women in the U.S. are gradually delaying marriage. This has happened as a result of various factors including the rise in cohabitation as a prerequisite for (or instead of) marriage, increasing fear of divorce (largely from children who grew up with divorced parents), rising educational attainment, spending longer in education, and rising labor force participation for women. The increasing delay in marriage could be due to today’s young adults having priorities other than marriage or wanting to attain certain accomplishments, such as education, earnings, or a career before getting married or wanting more time for leisure or finding the right partner.

But young adults may also be delaying marriage due to increasing difficulty in attaining the financial stability and socioeconomic capital that make young men and women marriageable.

Most young adults consider financial readiness an important factor when deciding when to get married. About seven in 10 men and women believe that it is important for a man to be able to financially support his family.REF A Pew Research Center survey from 2019 found that more than half of non-engaged cohabiting adults who wanted to be married someday cited a lack of financial readiness as a reason why they have not married yet.REF

There is also evidence that attaining financial readiness for marriage may be more difficult now than 10 or 20 years ago. Since the COVID-19 pandemic, home affordability has declined considerably.REF Student loan debt as a percentage of personal income, while less now than it was before the start of the pandemic, is still much higher than it was 15 years ago.REF And while the wealthiest millennials have acquired more wealth than their counterparts from the baby-boom generation, the wealth of a majority of millennials, particularly the working-class, has declined relative to baby boomers.REF

If today’s young adults are delaying marriage simply because they are unable to establish themselves in their careers with enough savings to pay off college loans and afford a car and a place to live, these are economic problems. Economic problems could perhaps be addressed through free-market-friendly policy solutions that do not place additional tax burdens on Americans or add to the federal debt as misguided solutions, such as student loan forgiveness, would do.REF Reducing financial obstacles to marriage could potentially increase the U.S. total fertility rate and improve life satisfaction among young adults struggling to find a partner and have a family.

The rise in cohabitation as a prerequisite for marriage, the increasing time spent in cohabitation, and the reduced likelihood of cohabitation transitioning to marriage have all also been responsible for the delay in marriage among U.S. adults.REF Cohabiting couples tend to have fewer children than married couples do.REF Couples who use cohabitation as a stepping-stone to marriage experience less marital satisfaction and less relationship stability than couples who do not live together before engagement.REF Couples who cohabit (regardless of future intentions to marry) also tend to have less relationship satisfaction and stability than couples who are married.REF As a result, public policy should discourage cohabitation and support the institution of marriage. Prioritizing marriage could help to reduce the median age of first marriage, increase total fertility, build stronger family units less susceptible to relationship dissolution, and improve life and relationship satisfaction.

As Charts 6 and 7 make clear, marriage as an institution, in general, is in decline across all age groups and generations. Without a substantial rise in marriage among reproductive-age women, or dramatic increases in childbearing among currently married couples, it is unlikely that the fertility rate will return to the replacement level unless there are dramatic increases in unwed childbearing accompanied by the resulting societal costs this would entail. However, policymakers should not rely on the promotion of marriage as a panacea for low fertility. Married couples also appear to be experiencing pressures that are causing them to put off childbearing. As shown in Chart 5, fertility rates have decreased slightly among married women in their prime childbearing years since 2017. It would appear that marriage does not make couples immune to the factors causing the postponement of fertility in the population at large, but any potential impacts on married fertility are much less than on the population on the whole.

The current age structure of the population has primed the U.S. for a potential mini baby boom. The cohort of women between 30 and 34 years of age is now the largest age group of women in their childbearing years. Another large cohort of women are projected to enter their late twenties by 2027, and by 2031 the population of women in their early thirties is projected to be the largest cohort of reproductive age women under 40 in history.REF This cohort will soon enter peak childbearing years. Both of these cohorts saw declining fertility rates during their early to late twenties, an indication that these women may have been postponing births. While the total fertility rate has declined in recent years, Americans’ ideal family size has not—perhaps an indication that women would like to have more children than they are on track for having.REF If the desire for children among women soon to enter their peak childbearing years has not diminished relative to past cohorts, public policies aimed at helping couples achieve their desired fertility could have their greatest impact if implemented now and over the next 10 years.

Jonathan Abbamonte is Senior Research Associate in the Center for Data Analysis at The Heritage Foundation.

Appendix: References for Charts 1–9

Chart 1

Joyce A. Martin et al., “Births: Final Data for 2015,” National Vital Statistics Reports, Vol. 66, No. 1 (January 5, 2017).

Michelle J.K. Osterman et al., “Births: Final Data for 2022,” National Vital Statistics Reports, Vol. 73, No. 2 (April 4, 2024).

Brady E. Hamilton, Joyce A. Martin, and Michelle J.K. Osterman, “Births: Provisional Data for 2023,” Vital Statistics Rapid Release, No. 35 (April 2024).

Chart 2

U.S. Centers for Disease Control and Prevention, CDC WONDER database, “Natality Information: Live Births,” https://wonder.cdc.gov/natality.html (accessed December 11, 2024).

U.S. Census Bureau, “Dataset: ACS 1-Year Estimates Public Use Microdata Sample,” 2004–2023, https://data.census.gov/mdat/#/ (accessed December 11, 2024).

Chart 3

U.S. Centers for Disease Control and Prevention, CDC WONDER database, “Natality Information: Live Births,” https://wonder.cdc.gov/natality.html (accessed December 11, 2024).

Chart 4

U.S. Census Bureau, “Historical Marital Status Tables,” Table MS-2. Estimated Median Age at First Marriage, by Sex: 1890 to the Present,” https://www. census.gov/data/tables/time-series/demo/families/marital.html (accessed January 2, 2025).

Chart 5

U.S. Centers for Disease Control and Prevention, CDC WONDER database, “Natality Information: Live Births,” https://wonder.cdc.gov/natality.html (accessed December 11, 2024).

U.S. Census Bureau, “Dataset: ACS 1-Year Estimates Public Use Microdata Sample,” 2004–2023, https://data.census.gov/mdat/#/ (accessed December 11, 2024).

Chart 6

U.S. Census Bureau, “Dataset: ACS 1-Year Estimates Public Use Microdata Sample,” 2004–2023, https://data.census.gov/mdat/#/ (accessed December 11, 2024).

Chart 7

U.S. Census Bureau, “Dataset: ACS 1-Year Estimates Public Use Microdata Sample,” 2004–2023, https://data.census.gov/mdat/#/ (accessed December 11, 2024).

Chart 8

U.S. Census Bureau, “Annual State Resident Population Estimates for 5 Race Groups (5 Race Alone or in Combination Groups) by Age, Sex, and Hispanic Origin: April 1, 2020 to July 1, 2023,” State Characteristics Population Estimates, July 1, 2023.

U.S. Census Bureau, “Annual Resident Population Estimates for 5 Race Groups (5 Race Alone or in Combination Groups) by Age, Sex, and Hispanic Origin for States and the District of Columbia: April 1, 2010 to July 1, 2020,” State Characteristics Population Estimates, July 1, 2020, updated July 2021.

Chart 9

Joyce A. Martin et al., “Births: Final Data for 2015,” National Vital Statistics Reports, Vol. 66, No. 1 (January 5, 2017).

Michelle J.K. Osterman et al., “Births: Final Data for 2022,” National Vital Statistics Reports, Vol. 73, No. 2 (April 4, 2024).

Brady E. Hamilton, Joyce A. Martin, and Michelle J.K. Osterman, “Births: Provisional Data for 2023,” Vital Statistics Rapid Release, No. 35 (April 2024).