Skip to content

3. Fertility Assumptions, 2012-based National Population Projections This product is designated as National Statistics

Released: 06 November 2013 Download PDF

Introduction

This report provides detailed information on the principal and variant fertility assumptions used in the 2012-based national population projections. For England, and for Wales, the long-term average completed family size is assumed to be 1.90 children per woman. A higher level of 2.00 is assumed for Northern Ireland and a lower level of 1.75 is assumed for Scotland. These assumptions represent an increase compared with the 2010-based projections for England, Northern Ireland, Scotland and Wales.

Principal Assumptions

The numbers of births for the projections are obtained by applying the appropriate fertility rate to the average number of women at each age during each year of the projection period. Because cohort fertility rates are more stable than those for calendar years (period rates), the fertility rates used in the projections are derived from assumptions relating to the year in which women were born. The assumptions about completed family size are based on family building patterns to date and other relevant evidence.

Tables 3-1 to 3-3 show average completed family size, births per 1,000 women, achieved family size, and average age at motherhood, by year of birth of woman.

Table 3-1: Completed family size for the constituent countries of the United Kingdom

Year of birth of woman
1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 & later
England 2.06 2.02 1.98 1.91 1.91 1.91 1.97 2.00 2.00 1.93 1.91 1.90 1.90
Wales 2.10 2.05 1.99 1.96 1.94 1.92 1.94 1.98 2.00 1.92 1.91 1.90 1.90
Scotland 2.08 1.95 1.87 1.80 1.74 1.73 1.75 1.77 1.77 1.75 1.76 1.75 1.75
Northern Ireland 2.87 2.65 2.42 2.22 2.11 2.00 2.12 2.08 2.07 2.03 2.01 2.00 2.00
United Kingdom 2.09 2.03 1.98 1.91 1.90 1.90 1.96 1.98 1.98 1.92 1.90 1.89 1.89

Table notes:

  1. Figures in bold are partly or wholly projected.

Download table

Table 3-2: Births per 1,000 women by age, United Kingdom

Year of birth of woman
Ages   1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 & later
Under 20   231 221 156 133 152 147 154 135 128 96 87 81 80
20 - 24   699 561 527 457 418 361 346 357 350 321 318 316 315
25 - 29   634 650 630 594 522 469 499 517 519 509 506 504 504
30 - 34   365 403 438 454 466 534 561 566 574 579 580 580 580
35 - 39   132 163 190 216 276 314 322 328 332 335 335 335 336
40 & over   28 36 43 57 70 73 75 76 77 77 77 77 77
 
Average  
family size   2.09 2.03 1.98 1.91 1.90 1.90 1.96 1.98 1.98 1.92 1.90 1.89 1.89

Table notes:

  1. Figures in bold are partly or wholly projected.

Download table

Table 3-3: Achieved family size by exact age, and average age at motherhood, United Kingdom

Year of birth of woman
Ages 1950 1955 1960 1965 1970 1975 1980 1985 1990 1995 2000 2005 2010 & later
20 0.23 0.22 0.16 0.13 0.15 0.15 0.15 0.14 0.13 0.10 0.09 0.08 0.08
25 0.93 0.78 0.68 0.59 0.57 0.51 0.50 0.49 0.48 0.42 0.40 0.40 0.40
30 1.56 1.43 1.31 1.18 1.09 0.98 1.00 1.01 1.00 0.93 0.91 0.90 0.90
35 1.93 1.84 1.75 1.64 1.56 1.51 1.56 1.57 1.57 1.51 1.49 1.48 1.48
40 2.06 2.00 1.94 1.85 1.83 1.83 1.88 1.90 1.90 1.84 1.83 1.82 1.81
45 2.09 2.03 1.98 1.91 1.90 1.89 1.95 1.97 1.97 1.91 1.90 1.89 1.89
Total
family size 2.09 2.03 1.98 1.91 1.90 1.90 1.96 1.98 1.98 1.92 1.90 1.89 1.89
Mean age at
motherhood
(years) 26.4 27.1 27.8 28.4 28.8 29.4 29.5 29.6 29.7 30.0 30.1 30.2 30.2

Table notes:

  1. Figures in bold are partly or wholly projected.

Download table

The equivalent tables for the constituent countries of the UK, England & Wales, and Great Britain can be found in the data download links.
 
For the UK as a whole, completed family size showed a sharp decline from an average of around 2.45 children for women born in the mid 1930s to just over 2 for women born in the 1950s. Since then, the completed family size has declined gradually, with women born in 1967, effectively the most recent cohort to have completed their fertility, achieving an average of 1.9 children per woman.

The family sizes to be achieved by women currently in their twenties or younger are highly conjectural, but there is some evidence that falls in cohort fertility could be slowing down. In particular, women born in 1980 have had more children on average by age 30 than those born in 1975 and, because fertility rates at older ages are projected to remain high, the 1980 cohort is projected to have 1.96 children on average, a higher completed family size than women born in the 1970s. For women born after 1980, it has been assumed that average completed family size for the UK as a whole will initially increase slightly before eventually levelling off at 1.89 children for women born after 2010.

For England, and for Wales, the long-term average completed family size is assumed to be 1.90 children per woman. A higher level of 2.00 is assumed for Northern Ireland and a lower level of 1.75 is assumed for Scotland. These assumptions represent an increase compared with the 2010-based projections for Northern Ireland, Scotland, England and Wales.

Between 2002 and 2008, total fertility rates increased in all constituent countries of the UK, followed by a dip in 2009 (see Figure 3-1). All countries except Scotland then showed a recovery in 2010 with Wales showing another dip in 2011. For the latest projections, the total fertility rate for the UK has been assumed to decrease slightly from 2012 to 2013 then stabilise at 1.89 from then on.

Over the past ten years, fertility rates have generally been rising faster among women in their thirties and forties than for women in their twenties, so mean age at childbirth has continued to rise. The average age at motherhood for the UK as a whole is projected to increase from 28.4 years for women born in 1965 to its long-term level of 30.2 years for those born from 2010 onwards.

Figure 3-1 shows the average completed family size (CFS) and the total fertility rate (TFR), which is defined as the average number of children that would be born per woman if all women lived to the end of their child bearing years and experienced the exact current age-specific fertility rates throughout their lifetime, for the UK between 1973 and 2037.

Figure 3-1: Total fertility rate and average completed family size, United Kingdom, 1973-2037

Figure 3-1: Total fertility rate and average completed family size, United Kingdom, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland and the UK for 2002–2010 were not available at the time of projection.
  3. Completed family size (CFS) relates to cohort born 30 years earlier - 30 years being the approximate mid-point of the childbearing ages. Projected completed family size is given for cohorts who have not yet completed childbearing.

Download chart

The equivalent figures for the constituent countries of the UK can be found in the relevant chart section.

Figure 3-2 shows the assumed ultimate (long-term) age-specific fertility rates for the constituent countries of the UK.

Figure 3-2: Assumed ultimate (long-term) age-specific fertility rates

Figure 3-2: Assumed ultimate (long-term) age-specific fertility rates

Notes:

  1. All fertility data are displayed on a calendar year basis.

Download chart

 

Figure 3-3 shows the estimated and assumed average completed family size for women born between 1943 and 2007 for the constituent countries of the UK.

Figure 3-3: Estimated and assumed average completed family size, women born 1943-2007

Figure 3-3: Estimated and assumed average completed family size, women born 1943-2007

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland for 2002–2010 were not available at the time of projection.

Download chart

 

Figure 3-4 shows the estimated and assumed total fertility rates for the constituent countries of the UK between 1973 and 2037.

Figure 3-4: Estimated and assumed total fertility rates, 1973-2037

Figure 3-4: Estimated and assumed total fertility rates, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland for 2002–2010 were not available at the time of projection.

Download chart


 

Assumptions for Fertility Variants

Table 3-4 shows the assumed long-term total fertility rates for the standard variants and special case scenarios for the UK and its constituent countries. The replacement fertility and constant fertlity variants are due to be published on 10 December 2013.

Table 3-4: Assumed long-term total fertility rates for the standard variants and special case scenarios

Standard variants  Special case scenarios
High Principal Low Replacement fertility Constant fertility
         
England 2.10 1.90 1.70 2.075 1.90
Wales  2.10 1.90 1.70 2.075 1.86
Scotland 1.95 1.75 1.55 2.075 1.64
Northern Ireland 2.20 2.00 1.80 2.075 1.98
United Kingdom 2.09   1.89   1.69   2.075   1.88

Table notes:

  1. Constant fertility is taken from the 2012-13 total fertility rate and applied throughout the projection period.

Download table

For the standard variants, fertility rates are assumed to move gradually from current levels to those assumed for the long-term. For Scotland and the UK, the high variants assume an initially dampened increase in total fertility rates to the year ending mid-2013, followed by a more smooth increase to the long-term ‘high’ level. For the UK and its constituent countries, the low variants assume that total fertility rates show a smooth transition to their projected long-term levels.

For the special case scenarios, the fertility levels given in the table are applied throughout the projection period, that is, from the year ending mid-2013 onwards.

Figure 3-5 shows estimated and assumed total fertility rates for the UK between 1973 and 2037 for the principal projection and high and low variants.

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, United Kingdom

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, United Kingdom

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland and the UK for 2002–2010 were not available at the time of projection.

Download chart

 

The equivalent figures for the constituent countries of the UK can be found in the relevant charts section.

Background notes

  1. Revised population estimates for 2002-2010 based on the 2011 Census are not yet available for Scotland so assumptions have been set using fertility rates for Scotland over this period based on estimates rolled forward from the 2001 Census. Analysis of the 2011 Census results has not highlighted any concerns with taking this approach.

    More information on the differences between the 2011 Census and the mid-year estimates for 2001 for Scotland can be found in the NRS reconciliation report at http://www.gro-scotland.gov.uk/statistics/theme/population/2011-census-reconciliation-report/index.html.

  2. Details of the policy governing the release of new data are available by visiting www.statisticsauthority.gov.uk/assessment/code-of-practice/index.html or from the Media Relations Office email: media.relations@ons.gsi.gov.uk

    These National Statistics are produced to high professional standards and released according to the arrangements approved by the UK Statistics Authority.

Appendix A: England Charts

Figure 3-1: Total fertility rate and average completed family size, England, 1973-2037

Figure 3-1: Total fertility rate and average completed family size, England, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Completed family size (CFS) relates to cohort born 30 years earlier - 30 years being the approximate mid-point of the childbearing ages. Projected completed family size is given for cohorts who have not yet completed childbearing.

Download chart

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, England

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, England

Notes:

  1. All fertility data are displayed on a calendar year basis.

Download chart

Appendix B: Wales Charts

Figure 3-1: Total fertility rate and average completed family size, Wales, 1973-2037

Figure 3-1: Total fertility rate and average completed family size, Wales, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Completed family size (CFS) relates to cohort born 30 years earlier - 30 years being the approximate mid-point of the childbearing ages. Projected completed family size is given for cohorts who have not yet completed childbearing.

Download chart

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Wales

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Wales

Notes:

  1. All fertility data are displayed on a calendar year basis.

Download chart

Appendix C: Scotland Charts

Figure 3-1: Total fertility rate and average completed family size, Scotland, 1973-2037

Figure 3-1: Total fertility rate and average completed family size, Scotland, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland for 2002–2010 were not available at the time of projection.
  3. Completed family size (CFS) relates to cohort born 30 years earlier - 30 years being the approximate mid-point of the childbearing ages. Projected completed family size is given for cohorts who have not yet completed childbearing.

Download chart

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Scotland

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Scotland

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Figures for 2002-2010 are due to be revised to take account of the 2011 Census for Scotland. Revised population estimates for Scotland for 2002–2010 were not available at the time of projection.

Download chart

Appendix D: Northern Ireland Charts

Figure 3-1: Total fertility rate and average completed family size, Northern Ireland, 1973-2037

Figure 3-1: Total fertility rate and average completed family size, Northern Ireland, 1973-2037

Notes:

  1. All fertility data are displayed on a calendar year basis.
  2. Completed family size (CFS) relates to cohort born 30 years earlier - 30 years being the approximate mid-point of the childbearing ages. Projected completed family size is given for cohorts who have not yet completed childbearing.

Download chart

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Northern Ireland

Figure 3-5: Estimated and assumed total fertility rates, 1973-2037, Northern Ireland

Notes:

  1. All fertility data are displayed on a calendar year basis.

Download chart

Get all the tables for this publication in the data section of this publication .
Content from the Office for National Statistics.
© Crown Copyright applies unless otherwise stated.