Cohort Fertility: 2010

Fertility by year of birth of mother, not the year of birth of child. Includes data on the number of live-born children and women remaining childless.

Nid hwn yw'r datganiad diweddaraf. Gweld y datganiad diweddaraf

Email Julie Jefferies

Dyddiad y datganiad:
16 December 2011

Cyhoeddiad nesaf:
7 March 2013

1. Key findings

  • The average completed family size for women born in 1965 and completing their childbearing in 2010 was 1.91 children per woman. This compares with their mothers’ generation, represented by women born in 1938, who had on average 2.39 children

  • Two children was the most common family size for women born in both 1938 and 1965

  • The level of childlessness among women born in 1965 is higher than for women born in 1938. One in five women born in 1965 remained childless, compared with one in nine born in 1938

  • One in ten women born in 1965 had four or more children, compared with one in five women born in 1938

  • Women born in 1980 have had slightly fewer children on average (1.03) by their 30th birthday than women born in 1965 who had 1.18 children by the same age

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2. Introduction

This bulletin presents statistics on childbearing patterns of women in England and Wales. These figures are presented by the year of birth of mother - for ‘cohorts’ of women born in the same year - rather than by the year of birth of child. The estimates have been updated with 2010 births, the latest data available, which means that completed family size for women born in 1965 is presented for the first time.

This statistical bulletin provides supporting commentary for the Cohort fertility package which includes data tables on:

  • average number of live-born children, age and year of birth of woman, 1920-1995,

  • proportion of women who have had at least one live birth, age and year of birth of woman, 1920-1995,

  • percentage distribution of women of childbearing age by number of live-born children, age and year of birth of woman, 1920-1991,

  • age-specific fertility rates, age and year of birth of woman, 1920-1995.

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3. What is cohort fertility?

A cohort is a group of women born in the same year. Cohort fertility analyses explore whether current generations of women of childbearing age are reaching, exceeding or falling short of the fertility levels of previous generations. This bulletin contains statistics on changes in average family size for past, present and future cohorts, levels of childlessness for different cohorts of women, and the proportions of women having one, two or more children.

The key cohort presented here is women born in 1965, who were aged 45 in 2010. This is the most recent cohort that is assumed to have completed their childbearing (see note 1). This statistical bulletin compares the completed family size of women born in 1965 with that of their mothers’ generation; the average age of mothers giving birth in 1965 was 27 years, and women of that age were born in 1938.

Women born in 1980, who have reached age 30 in 2010, are also used as a comparison group, as age 30 may be considered the mid-point of childbearing age (see note 2). This bulletin compares the achieved fertility of the 1980 cohort by this age with that of previous cohorts by the same age. It also presents their projected completed family size, comparing it with earlier cohorts.

Notes for what is cohort fertility?

  1. A woman is assumed to have completed her childbearing by the last day she is aged 45, i.e. by her 46th birthday (exact age 46). Completed fertility includes fertility rates up to and including age 45. See background note 2 for a more technical explanation.

  2. The ages of women are presented in 'exact years'. Therefore figures should be interpreted as the average number of children a woman has had up to that birthday. So childbearing up to exact age 30 includes cumulative fertility through her lifetime up to the day before her 30th birthday. Any childbearing in the 12 months from her 29th birthday onwards will be included in fertility up to exact age 30. See background note 2 for a more technical explanation.

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4. Average family size

The average number of live-born children a woman has by the end of her childbearing years (completed family size) has been falling for recent cohorts (Figure 1). Women born in 1965 had on average 1.91 live-born children. This compares with women born in the 1930s and 1940s, who had on average between 2.1 and 2.4 children. Cohorts of women born from 1958 onwards have had on average fewer than two children per woman. This decrease in the average family size is mainly due to rising levels of childlessness rather than any decrease in family size among women who have children. Childlessness is discussed further in the next section.

The average number of children women have had up to their 30th birthday can give an indication of more recent trends in family size. The 1965 cohort had 1.18 children on average by their 30th birthday, compared with 1.86 by the same age for their mother’s generation, the 1938 cohort. Overall, women born in the 1960s and 1970s have had fewer children by age 30 than previous generations. This reflects their postponement of childbearing to older ages (see note 1), for reasons including:

  • increased participation in higher education

  • delayed marriage and partnership formation, and

  • the desire to establish a career, get on the housing ladder and ensure financial stability before starting a family.

However, Figure 1 shows a slight upturn in average family size by the 30th birthday for the most recent cohorts, from 0.99 children for the 1975 cohort to 1.03 for the 1980 cohort. This is mainly because women born in 1980 had higher fertility in their late twenties than those born in 1975. There is no single explanation for this increase, but possible reasons include the changes in support for families introduced by the previous government (such as tax credits and maternity/paternity leave), and the increasing proportion of women aged 25-29 who were born outside the UK (with above-average fertility) (see note 2).

Notes for average family size

  1. Jefferies, J (2008). Fertility assumptions for the 2006-based national population projections. Population Trends 131, pp 19–27, Spring 2008 (297 Kb Pdf)

  2. Tromans N, Natamba E and Jefferies J (2009), Have women born outside the UK driven the rise in UK births since 2001? Population Trends 136, pp 28–42, summer 2009 (2.08 Mb Pdf)

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5. Childlessness

Childlessness is estimated as the proportion of women who have not had a live birth by a specific age.

Figure 2 shows that the level of childlessness for women born in 1965 is at a 45-year high and comparable with that of women born in 1920 by completion of childbearing. One in five women born in 1965 (and 1920) remained childless by the end of their childbearing years compared with one in nine women born in 1938. A wide range of explanations relating to circumstances and choices have been put forward for the increasing childlessness seen in recent cohorts. These include the decline in the proportion of women married, changes in the perceived costs and benefits of childrearing versus work and leisure activities, greater social acceptability of the childfree lifestyle and the postponement of decisions about whether to have children until it may be biologically too late (see note 1).

By their 30th birthday, 45 per cent of the 1980 cohort were childless, a slightly higher proportion than for the 1965 cohort at the same age (42 per cent). This highlights the trend that women have been increasingly delaying having children to older ages. However, Figure 2 shows that the proportion of women who are childless has been falling for successive cohorts born from 1975 onwards (when 48 per cent of women had not had a live birth by age 30). This suggests a slight reversal and reflects the higher levels of childbearing among women in their late twenties born in 1980 compared with those born five years earlier.

Notes for childlessness

  1. For reasons for increasing childlessness, see for example:

    O'Leary L, Natamba E, Jefferies J and Wilson, B (2010) Fertility and partnership status in the last two decades, Population Trends 140, pg 5-35

    Simpson, R (2009) Delayed childbearing and childlessness in Britain, in Stillwell, J, Kneale, D and Coast, E (eds.) Fertility, Living Arrangements, Care and Mobility Understanding Population Trends and Processes Volume 1, Springer, Dordrecht, pp. 23-40

    McAllister, F with Clarke, L, The Family Policy Studies Centre (1998). Choosing Childlessness. Joseph Rowntree Foundation. A summary is available

    Basten, S (2009). Voluntary childlessness and being Childfree. The Future of Human Reproduction: Working Paper #5

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6. Number of children

The traditional two-child family remains the most common family type, with 38 per cent of women born in 1965 having two children (Figure 3, Table B). After two children, childlessness is the second most common family size for the 1965 cohort. This is a recent development first encountered among the 1964 cohort, whereas for those born between the late 1930s and early 1960s, three children was the second most common family size. A woman born in 1938 was more likely to have one, three or ‘four or more’ children than not to have any. Only one in ten women born in 1965 had four or more children, compared with nearly one in five in the 1938 cohort (Table A).

The proportion of women with a one-child family remained relatively stable for women born between 1940 and 1965 with 13 per cent of women born in 1965 having a one-child family. ‘Only’ children were most common for women born in the 1920s, where around one-fifth had one child – this may be because their marriage and childbearing was delayed or disrupted by World War II. For women born in the years from 1938 to 1965, between 12 and 14 per cent had only one child by the time they had completed their childbearing. Further information on only children is available in a published summary.

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7. The changing pattern of fertility

Looking at the fertility rates of selected cohorts at particular age milestones highlights how the age distribution of women giving birth has varied over time. As an example, the two vertical lines on Figure 4 allow a comparison of the age profile of fertility in the 1965 cohort, who have completed their childbearing, with that of the 1980 cohort to date.

For the 1965 cohort the highest fertility rate of those shown was at the age of 25, closely followed by age 30. A lower level of fertility was recorded at the age of 20, while the number of live births per 1,000 women at the age of 35 was even lower. On average the 1965 cohort had 1.91 children per woman.

Age-specific fertility rates for the 1980 cohort are currently only available up to the age of 30. For this cohort, fertility rates at age 30 were much higher than for the 1965 cohort and at a level last encountered by women born in the mid 1930s. In contrast, fertility at age 20 was similar to the 1965 cohort, while at the age of 25 it was much lower in the 1980 cohort than for the 1965 cohort.

Fertility at age 25 hit a low for women born in 1977 before rising slightly among cohorts born between 1978 and 1984. Consequently, 25 year olds born in 1980 had 25 per cent fewer live births per 1,000 women at this age than 25 year olds who were born in 1965.

If recent trends continue, the 1980 cohort would be expected to have an older average age at childbearing than the 1965 cohort. The projected completed family size for women born in 1980 is explored in the next section.

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8. Projected future family size

Assumptions on the future fertility of women in England and Wales underpinned the 2010-based National Population Projections published by ONS in October 2011 (see note 1). The following projections of family size for cohorts who have not yet finished their childbearing come from the birth order probability model (a method of projecting forward current trends in birth order) that was used to produce the fertility assumptions for the 2010-based population projections.

It is projected that average completed family size, which was 1.91 for the 1965 cohort, will fluctuate around this level for women born in the late 1960s and early 1970s. It is then projected to increase to 2.01 for women born in 1980. Completed family size is expected to peak at 2.03 among women born in the early 1980s before reducing again for women born in the 1990s (Table C) (see note 2).

The percentage of women having just one child is projected to rise from 13 per cent among the 1965 cohort to 18 per cent for the 1970 and 1975 cohorts and stabilise thereafter at 17 per cent. At the same time the proportion of women who do not have any children is expected to start falling from 20 per cent among the 1965 cohort, reaching a low of 14 per cent for the 1980 cohort. As the proportions of childless women having a first birth have increased substantially over the last decade, these projections reflect recent trends. However, demographic behaviour is inherently uncertain so there is no certainty that these trends will continue.

It is this lower level of projected childlessness combined with a slight rise in two-child families that results in women born in the 1980s having a projected average completed family size of more than two children, a level last seen in women born in the mid-1950s. However the proportion of families with three or more children is expected to remain fairly constant, with 29 per cent of the 1965 cohort having three or more children and the same percentage projected for the 1980 cohort.

Notes for projected future family size

  1. The 2010-based National Population Projections were published on 26 October 2011.

  2. The higher average family sizes projected for the early 1980s cohorts reflects both their higher achieved fertility to date than for those born in the late 1970s at the same age, and the expectation that fertility among older women will remain high.

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9. Changes to this release of cohort fertility

For the 2010 release, woman’s age is presented in exact years (i.e. by an exact birthday), where previously it was presented in completed years. What was labelled age 29 in completed years previously, is now labelled as exact age 30 (including all cumulative fertility in the 29th year up to the 30th birthday). See below for further clarification.

These changes affect tables 1, 2 and 3 in the Cohort fertility release. Table 4 is unaffected. This change has been made in response to feedback from users and brings the tables into line with other demographic statistics.

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10. Further releases on live births in 2010 in England and Wales published on 16 December 2011

  • Characteristics of mother 2 – this package presents live birth statistics (numbers and rates) within and outside marriage/civil partnership. It also provides data on first live births by marriage/civil partnership duration, and live births within marriage/civil partnership by age of mother and number of previous live-born children.

  • Further parental characteristics – this package presents age-specific fertility rates for men, the mean age of father, and paternities within and outside marriage/civil partnership. See Characteristics of Mother 1 and 2 for birth statistics by age of mother, type of registration (within marriage/civil partnership, joint, sole) and number of previous live-born children.

  • Live births by socio-economic status of father – this package presents data on birth registrations in England and Wales by National Statistics Socio-economic Classification (NS-SEC) of father as defined by occupation.

Key findings from these releases:

  • The standardised mean age of father at birth of child has increased by nearly two years over the last two decades from 30.7 years in 1990 to 32.6 in 2010 (see notes 1 and 2). The standardised mean age of mother increased by a similar amount over the same period, from 27.7 in 1990 to 29.5 in 2010.

  • For men, the 30–34 age group had the highest fertility rate in 2010, the same age group that had the highest fertility rate for women. Previously, men in their mid-to-late twenties had the highest fertility rate but were overtaken in 1993 by men in their early thirties. The same trend occurred among women a decade later, with the fertility of women in their early thirties overtaking that of women in their mid-to-late twenties in 2004.

  • Women under 30 have a higher percentage of births outside marriage/civil partnership than older women, with the highest proportions at the youngest ages. In 2010, 96 per cent of births to women aged under 20 occurred outside marriage/civil partnership, compared with 58 per cent of births to women in their twenties, 30 per cent of births to women in their thirties and 37 per cent of births to women aged 40 and over.

  • Over the last decade, women aged 20 to 24 have seen the largest percentage point increase in the proportion of births outside marriage/civil partnership. In this age group, the proportion of births outside marriage/civil partnership has risen from 63 per cent in 2000 to 75 per cent in 2010. The proportion of births outside marriage/civil partnership has also increased markedly for women aged 25 to 29, from 35 per cent in 2000 to 46 per cent in 2010.

Notes for further releases on live births in 2010 in England and Wales published on 16 December 2011

  1. Measures of male fertility are estimated. The age of the father is not collected for births that are registered solely by the mother (5.9 per cent in 2010), therefore these ages are estimated. More information is available from the metadata in the Further parental characteristics package.

  2. The standardised mean age is a measure which allows fertility trends to be separated out from the effects of changes in the population’s age structure. It is therefore useful for comparing mean ages across population subgroups and over time.

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11. Users and uses of birth statistics

The Office for National Statistics uses birth statistics to:

  • produce population estimates and population projections, both national and subnational

  • produce marital status estimates

  • quality assure census estimates

  • report on social and demographic trends

Other key users of birth statistics include the Department for Education and the Department of Health. Other users include academics, demographers, health researchers, lobby groups, international organisations and the media.

Cohort fertility statistics and estimates of fertility by family size are primarily used by ONS for producing the fertility component of population projections and for reporting on social and demographic trends.

The Department for Work and Pensions uses information on family size for modelling future lone parents, pensions and benefits.

Estimates of childlessness are of interest to policymakers concerned with the support and care available to people at older ages. Estimates of family size are of use to special interest groups such as organisations and networks supporting large families and for people who are, or who have, an only child.

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.Further information

Figures in this release are based on all live births registered in England and Wales. However due to the method of estimating true birth order for certain tables (see note 1), these figures cannot be disaggregated separately for England only and Wales only.

Further birth statistics for 2010 are available on the Office for National Statistics (ONS) website as follows:

The Birth summary tables (published 13 July 2011) provide summary figures including the number of live births and stillbirths, fertility rates, percentage of live births outside marriage/civil partnership, mean age of mother and percentage of live births to non-UK born mothers. Live births (number and rate) are also provided by age of mother and by local area.

The Parent's country of birth package (published 25 August 2011) provides statistics on country of birth of mother, country of birth of father, country of birth of mother by local authority and Total Fertility Rates for UK born women and non-UK born women.

The Characteristics of birth 1 package (published 15 September 2011) provides statistics on stillbirths by age of parents and quarter of occurrence, birthweight data for live and stillbirths by mother's area of usual residence and maternities, live births, and stillbirths in hospitals by area of occurrence.

The Live births by area of usual residence of mother package (published 15 September 2011) provides statistics on births for local authorities and health areas including figures by age of mother. An interactive mapping tool has been developed to help users analyse trends in fertility at the local area level. The interactive mapping tool can be found on the ONS website.

The Characteristics of mother 1 package was published on 20 October 2011. This provides summary statistics by age of mother, type of registration (within marriage/civil partnership, joint, sole), and mean age of mother by birth order.

The Characteristics of birth 2 package was published on 10 November 2011. This provides data tables on live births by month and quarter of occurrence, multiple births and place of birth.

A Fertility Summary – 2010 was published on 6 October 2011. This provides a comparison of total fertility rates and age-specific fertility rates in the four constituent countries of the UK and the EU15.

For information on data quality, legislation and procedures relating to birth statistics, please see Births Metadata 2010 (439.7 Kb Pdf) .

The ONS summary quality report for births (275.2 Kb Pdf) provides overview notes which pull together key qualitative information on the various dimensions of quality as well as providing a summary of methods used to compile birth statistics.

There is also a frequently asked questions on births and fertility (198 Kb Pdf) document.

Notes for further information

  1. Estimates of childlessness and number of children are based on estimates of true birth order. At birth registration, the number of previous births is only collected from married women. This partial information on birth order from registration data is supplemented with data from the General Lifestyle Survey (formerly known as the General Household Survey) to give estimates of true birth order for all women. More information is available from the metadata in the Cohort fertility package
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.Data available for the UK

Quarterly and annual summary birth statistics for the UK and its constituent countries can be found in the Population and Health Reference tables.

National Records of Scotland provides more detailed birth statistics for Scotland.

The Northern Ireland Statistics and Research Agency provides more detailed birth statistics for Northern Ireland.

Cumulative fertility by cohort is available for: Scotland and Northern Ireland

UK cohort figures are not published annually, but some limited UK cohort figures are available as part of the 2010-based National Population Projections release.

For England and Wales, birth statistics are based on the number of births occurring in the quarter/year, while Scotland and Northern Ireland statistics relate to the number of births registered in the quarter/year. The differences between reporting occurrences and registrations are relatively minor and figures are broadly comparable. Figures for the UK are produced by ONS compiling data for England and Wales, Scotland and Northern Ireland.

Each constituent country publishes provisional quarterly birth summary statistics throughout the year while more detailed annual birth statistics are published once the annual dataset is complete and has been quality assured. The ONS publishes quarterly and annual birth statistics summary tables for the UK with breakdowns for each constituent country in the Population and Health Reference tables. Collating all the data together in one place enables users to easily compare trends for the UK and its constituent countries.

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.Background notes

  1. Cohort fertility analysis allows the fertility experience of a group of women sharing the same year of birth (a cohort) to be traced through time and compared with the experience of other cohorts. Statistics relating to the family building of women born in given years shed light on the trends underlying year-to-year changes in fertility and are particularly valuable in helping to formulate models of future fertility.

    Period measures of fertility, such as the Total Fertility Rate (TFR), provide a timely snapshot of the intensity of childbearing in a particular year. However the TFR should not be interpreted as a measure of family size because it is affected by the timing of childbearing. The TFR is likely to under or overestimate average family size during periods where women are delaying having children or later catching up. Cohort fertility analysis may not be as timely, but provides an accurate measure of trends in family size.

    The TFR in England and Wales of 2.00 children per woman in 2010 represents the current level of childbearing among women of all childbearing ages. The average family size of 1.91 children is for women who have completed their childbearing in 2010. The two measures should not be directly compared for the reasons noted above.

  2. Completed fertility is the sum of age-specific fertility rates for ages 15 to 45 and therefore relates to fertility up to the 46th birthday. In this bulletin the 1965 cohort, who are aged 45 in 2010, are presented as the latest to complete their fertility up to the 46th birthday. Although women born in 1965 will not reach their 46th birthday until 2011, the age-specific fertility rate at age 45 includes births to women aged from 45 years and 0 days to 45 years and 364 days in 2010 and thus fertility up to (but not including) the 46th birthday.

    In calculating estimates of completed family size for women born in different years, an assumption must be made about the year each woman was born, based on her age when she gives birth. In this case it is assumed that births at age 45 in 2010 are to women born in 1965. This assumption is necessary because information on the mother’s year of birth is not available in historic births datasets so has to be assumed from the age of the mother when she gives birth. However women giving birth at age 45 during 2010 were actually born between January 1964 and December 1965 – half of these women will have their 45th birthday in 2010 (those born in 1965 who give birth after their 45th birthday,) and half will have their 46th birthday in 2010 (those born in 1964 who give birth before their 46th birthday). However for simplicity the latest cohort to complete their childbearing is presented as the 1965 cohort, with their completed fertility based on the sum of age-specific fertility rates from age 15 in 1980 to age 45 in 2010.

    Similarly, the bulletin presents fertility up to exact age 30 for the 1980 cohort and other cohorts, as age 30 may be considered the mid-point of childbearing age. However fertility up to the 31st birthday for the 1980 cohort is available in the published Tables 1 and 2 because cumulative fertility to exact age 31 includes the age-specific fertility rate for age 30 in 2010 (from Table 4).

  3. Special extracts and tabulations of births data for England and Wales are available to order for a charge (subject to legal frameworks, disclosure control, resources and agreements of costs, where appropriate). Such enquiries should be made to:

    Vital Statistics Outputs Branch (VSOB)
    Tel: +44 (0)1329 444 110

    Enquiries on Cohort Fertility should be made to:
    Fertility and Family Analysis Unit (FFAU)
    Tel: +44 (0)1329 444 677

  4. We would welcome feedback on the content, format and relevance of this release. If feedback relates to this Cohort fertility release, please send to:, if it relates to Characteristics of mother 2, Further parental characteristics or Live births by socio-economic status of father, please send feedback to:

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