How does your family size compare?

Mean age at first birth for US women has moved from 21.4 years in 1970 to 27.6 years in 2024, on CDC figures. In England and Wales the average age of all mothers, not only first-time ones, reached 31.1 in 2025 on ONS figures. Longer time in education, later marriage and a changed economic picture account for most of the drift, and it has been steady enough across five decades that no single cause explains it on its own. The first months after that birth have their own normal, and the baby crying calculator maps it.

Very common. The Census Bureau's 2024 survey puts 40.3% of US women aged 30 to 34 with no children. Most of them will not stay that way, because a large share have children in their late 30s or early 40s, and by ages 40 to 44 the figure has dropped to around 19%. No children at 30 sits squarely inside normal for this generation, whatever anybody at a wedding says about it.

The evidence is mixed and depends heavily on where you live. A study of World Values Survey data from 86 countries found happiness falling with the number of children on average, though the link turned positive for parents over 40. Where public support for families is strong, the dip for younger parents is smallest. Support systems, financial security, the state of the partnership and whether the timing was chosen all matter more than the count does.

Pew Research Center 2024 data put 57% of US adults under 50 who have no children and do not plan to on simply not wanting them, with smaller groups naming environmental, financial or health reasons. Among childless adults over 50, 38% said they had wanted children at some point and it did not happen. So a large slice of childlessness was never a choice. Rates are rising across high-income countries, most sharply among women with higher educational attainment.

Female educational attainment is one of the strongest predictors there is of a smaller completed family and a later first birth. ONS and CDC data both show the inverse relationship clearly, with women who hold graduate degrees finishing with fewer children than women who left education earlier. Part of that is mechanical, since years spent studying are years taken off the front of the childbearing window. The rest runs through career, income and priorities, and it holds across most countries once religious affiliation is controlled for.

Secondary infertility means being unable to conceive or carry a pregnancy after already having one or more biological children. CDC figures from the National Survey of Family Growth, 2015 to 2019, put infertility at about 6% of married women aged 15 to 49 who have already given birth. It tends to be lonelier than primary infertility, because people feel they have no standing to call it a struggle when there is a child in the house. Age-related decline, endometriosis, pelvic inflammatory disease, changed sperm parameters and complications from earlier deliveries all contribute, and it explains part of the gap between the family people wanted and the one they ended up with.

Among US women aged 40 to 44, the Census Bureau's 2024 survey puts about 17% at three children and about 13% at four or more. In England and Wales two children is the most common outcome, at 38% of women born in 1978, and three-child and bigger families have become much rarer in both countries since the 1970s. Large families now cluster in religiously observant households and in lower-income populations, in American and British data alike.

Two things run in opposite directions here. Down syndrome risk rises from approximately 1 in 900 at maternal age 30 to around 1 in 100 at age 40, and paternal age over 40 carries a slightly raised risk of autism spectrum disorder and some rare genetic mutations. Against that, children of older parents get more financial stability and more settled relationships, and population studies find modest advantages in educational attainment once socioeconomic status is controlled for. The biological risk is real, small in absolute terms, and partly offset.

No. The spoiled only child stereotype does not survive modern research. Meta-analyses put only children at least level with children who have siblings on intelligence, academic achievement and psychological adjustment, with small advantages showing up in achievement motivation and verbal ability. Cooperativeness scores do come out slightly lower, though the gap is small and tracks parenting style more than the absence of a brother. That old reputation has been revised heavily across the past two decades.

Both, and pulling them apart is hard. Housing costs, childcare costs and stagnant wages clearly matter, because surveys across high-income countries keep finding that people want more children than they have and name money first when asked why. But fertility is falling among high earners for whom money constrains nothing, which no purely economic account covers. Lesthaeghe's work on the Second Demographic Transition points at a value shift toward self-realisation and personal experience running alongside the financial squeeze rather than underneath it.

It depends on age and country more than on the count. Margolis and Myrskyla's study of World Values Survey data from 86 countries (2011, Population and Development Review) found happiness falls with the number of children on average, but the link runs from negative to neutral to positive after 40. For younger parents the dip was smallest where public support for families is strong.