The proportion of children born to unmarried mothers has increased significantly across countries tracked by the Organisation for Economic Co-operation and Development (OECD), reflecting long-term changes in family structures, social attitudes and partnership patterns.

Updated data from the OECD Family Database, released in October 2025, provides a clearer picture of these changes, with figures extending to 2023 for most countries and to 2024 for five countries.

The indicator measures the percentage of children born to mothers who were not legally married at the time of birth. It is compiled using information from national statistical offices and Eurostat.

A Major Shift Since 1970

In 1970, fewer than 10% of children were born outside marriage in 20 of the 25 countries with comparable data for both 1970 and 2023. Since then, the proportion has risen in every one of those 25 countries.

The figures demonstrate a substantial transformation in how families are formed across different societies. Marriage is no longer the only setting in which many couples choose to raise children, and births to unmarried mothers have become more common in numerous countries.

Spain illustrates the scale of this shift. The share of births outside marriage increased from just 1.4% in 1970 to 50% in 2023, meaning that half of all births in the country occurred to mothers who were not legally married.

Colombia Records the Highest Share in the Updated Data

The latest database update includes Colombia for the first time, with historical figures available from 1998 onward.

In 2023, approximately 87% of births in Colombia were to mothers who were not legally married, the highest proportion reported among the countries included in the updated dataset.

This figure highlights the considerable differences in family formation patterns between countries. However, births outside marriage do not necessarily mean that children are being raised by single parents. Many unmarried couples live together and raise their children in stable partnerships.

Why This Indicator Matters

Tracking births outside marriage provides researchers with a useful way to examine changes in family life over time. Long-term, internationally comparable statistics on unmarried couples living together are unavailable for many countries, making birth registration data an important source of evidence.

The indicator can help policymakers understand evolving household structures and assess whether family policies adequately address the needs of children and parents, regardless of marital status.

As family patterns change, governments may need to consider how parental leave, childcare support, tax arrangements and social benefits affect different types of households.

Understanding the Numbers

Although the upward trend is consistent across the 25 countries with comparable figures, the pace and scale of change differ considerably. Historical social norms, legal frameworks, economic conditions and attitudes toward marriage may all contribute to differences between countries.

The statistics measure marital status at the time of birth, rather than whether parents live together, remain in a relationship or subsequently marry. They should therefore be interpreted as an indicator of changing family formation rather than a direct measure of single parenthood.

The OECD’s updated figures offer valuable evidence of how family structures have evolved since 1970. The findings also underline the importance of developing inclusive family policies that respond to the circumstances of children and parents across different household arrangements.