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Population projections are calculations that show the future population size and structure based on assumptions about future trends in fertility, mortality and migration, derived from an analysis of recent demographic trends. They are produced first at national level and then by region and by local authority.

Publications

Annual Report of the Registrar General (Northern Ireland)
Department: Northern Ireland Statistics and Research Agency
Finalised data for all births, deaths, marriages, civil partnerships and divorces along with population data for the year in question.
Household Projections for Scotland
Department: National Records of Scotland
Forward projections of the number of households in each local authority area in Scotland up to 2031, by household type and age group.
Household Projections for Scotland's Strategic Development Plan Areas and National Parks
Department: National Records of Scotland
Household projection data
Local Authority Population Projections for Wales
Department: Welsh Government
Population projections provide estimates of the size of the future population, and are based on assumptions about births, deaths and migration.
Local Authority Population Projections for Wales (2006-based)
Department: Welsh Government
Population projections provide estimates of the size of the future population, and are based on assumptions about births, deaths and migration.
Marital Status Population Projections for England & Wales
Department: Office for National Statistics
Marital status projections are produced for England and Wales and cover both legal marital status and (opposite sex) co-residential cohabitation.
National Population Projections
Department: Welsh Government
Population projections provide estimates of the future population. Projections are based on assumptions about future fertility, life expectancy, international and domestic migration.
National Population Projections
Department: Office for National Statistics
National population projections by age and sex for the UK and constituent countries. Includes information on the principal (main) and variant (alternative scenario) projections for each country together with details of the fertility, mortality and migration assumptions on which they are based.
Northern Ireland Population Projections
Department: Northern Ireland Statistics and Research Agency
Population Projections for Northern Ireland by sex and single year of age.
Population Aged 50 and Over in Wales
Department: Welsh Government
This Statistical Bulletin provides an analysis of the population aged 50 and over in Wales.
Population Projections for National Parks in Wales
Department: Welsh Government
This statistical release analyses the results from the population projections for the three national parks in Wales: Brecon Beacons, Snowdonia and Pembrokeshire.
Population Projections for Scotland's Strategic Development Plan Areas and National Parks
Department: National Records of Scotland
Strategic Development Plan Areas and National Park data
Population Projections for Scottish Areas
Department: National Records of Scotland
Population projections for sub-national Scottish Areas
Population of 0-19 year olds in Wales
Department: Welsh Government
Provides an analysis of the population of 0-19 year olds in Wales.
Projected Population of Scotland
Department: National Records of Scotland
Population projections: components of change, dependants, births, deaths, population by sex and age group.
Sub-Northern Ireland Population Projections
Department: Northern Ireland Statistics and Research Agency
Sub-Northern Ireland Population Projections.
Sub-national Population Projections Scotland (2006 Based)
Department: National Records of Scotland
Summarises the Registrar General for Scotland's mid-2006 based population projections for the council and NHS board areas of Scotland.
Sub-national population projections
Department: Office for National Statistics
Subnational population projections use past trends to project forward the population to give an indication of the future population for 25 years from the base year. Available for local authorities and Primary Care Organisations.

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Overview

National population projections are produced for the UK and constituent countries by the Office for National Statistics (ONS) in consultation with the statistical offices for these countries. They project the population by single year of age and sex for 75 years into the future. They are made using trend-based assumptions of future levels of fertility, mortality and migration.

The national population projections are not forecasts and do not attempt to predict the impact that new or future government policies, changing economic circumstances or other factors might have on future demographic behaviour. The projections are produced every two years by ONS.

As well as population by age and sex, the national population projections calculate future numbers of births, deaths and migrants (by single year of age). The assumptions on projected fertility and mortality rates and calculated life expectancies are also available. Both principal projections (representing the most likely population outcome) and variant projections (based on plausible alternative assumptions) are produced.

Subnational population projections for England are produced by ONS and project forward population estimates to give an indication of future levels of population by age and sex at Government Office Region, local authority, Primary Care Organisation and strategic health authority level for 25 years into the future.

The projections are trend-based, making assumptions about future levels of fertility, mortality and migration based on levels observed over a five year reference period to the base year. Therefore, they give an indication of what the future population, by age and sex structure, might be if recent trends continue, and take no account of policy or development aims in areas.

Subnational population projections are produced, for England, every two years by ONS these are fully consistent (in terms of population and components of change) with the official national population projections. Subnational population projections are also produced; for Scotland by General Register Office for Scotland, for Northern Ireland by Northern Ireland Statistics and Research Agency and for Wales by Welsh Assembly Government.

The national and subnational population projections for England are used by the Communities and Local Government for the production of household projections.

Marital status projections are produced on an occasional basis for England and Wales only. They give, for 25 years ahead, the projected future population by age, gender and both legal marital status and (opposite sex co-residential) cohabitation.

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Technical Data

National population projections are made for successive years running from one mid-year to the next using the cohort component method, which can be summarised as:

Population (year x) + Births (between years x and y) – Deaths (between years x and y) + In-Migrants (between years x and y) – Out-Migrants (between years x and y) = Population (year y).

This method is in line with those used by other national statistics institutes and is supported by demographic and academic experts.

For each age, the starting population plus net inward migrants less the number of deaths produces the number in the population, one year older, at the end of the year. Survivors of those born during the year are then added. Age is defined as completed years at the last birthday. Migration, deaths and births are all assumed to occur evenly throughout the year.

The mid-year population estimates from each country are used as the starting population. The numbers of births, deaths and migrants are calculated using the assumptions of fertility, mortality and migration which are determined by a mixture of trend observation and extrapolation, and consideration of expert opinion, with actual data included in the calculation for the first year of the projection.

The projections are computed for each of the component countries of the UK and the results are added together to produce projections for England and Wales, Great Britain and the UK. Both principal projections (most likely population outcome) and variant projections (plausible alternative assumptions) are produced.

Subnational population projections for England also use a cohort component methodology. The basic principal is the same as that used for the national population projections but is conducted for each individual local authority in England. In addition, internal migration flows between local authorities are modelled using recent patient register information and the population moved around accordingly.

At each stage in the process the components of population change (births, deaths and migration) are constrained nationally to the levels for these shown in the assumptions used in the official national population projections. The assumptions on fertility rates, mortality rates and migration rates are derived from trends observed in these measures over the five year period leading up to the projection base year.

This methodology applies to the general population only. Special population types, including foreign and home Armed Forces, are dealt with separately and are assumed to remain static over the projection period.

The legal marital status projections are produced using a component methodology based on assumptions of underlying marriage, remarriage and divorce rates. They are produced using a multi-dimensional modelling system LIPRO developed by the Netherlands Interdisciplinary Demographic Institute (NIDI).

The model requires assumptions to be made for transitions between different marital statuses. In addition, assumptions have to be made about the marital status distribution for both deaths and net migration. These assumptions are specified as an initial set of marriage, divorce and mortality rates by marital status, single year of age and sex as derived from the previous year’s components of change data used by ONS to update the annual population estimates by marital status.

The projections are adjusted to satisfy a number of consistency constraints. These include internal ‘two-sex’ constraints (for example, that the number of men divorcing each year must equal the number of women divorcing) and the external constraint that the results of the legal marital status projection are fully consistent with the results of the national (age and sex) projections for England and Wales.

The cohabitation projections are made by making assumptions about the proportions cohabiting in each age, sex and legal marital status group and then applying these to the results of the legal marital status projection. The assumptions are based on an analysis of trends in the proportions cohabiting.

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Glossary

  • Assumptions

    Demographic trend-based projections of future fertility, mortality and migration levels upon which the population projections are based.

  • Base population

    A population estimate which is the starting point of a population projection. For national and subnational projections, the base population is a mid-year estimate which includes all usually resident persons within a given area, whatever their nationality. Members of HM Armed Forces in the UK are included, but members of HM Armed Forces and their families who are abroad are excluded. Foreign Armed Forces in the UK are included, with dependants if they are accompanied. 

  • Child Dependency Ratio

    The number of children per thousand persons of working age.

  • Children

    Individuals aged under 16 years.

  • Cohort component method

    Population projections are made for successive years running from one mid-year to the next. For each age, the starting population plus net inward migrants less the number of deaths produces the number in the population, aged one year older, at the end of the year. To this, the survivors of those born during the year are added. Age is defined as completed years at the last birthday.

  • Cohort life expectancy

    The average number of years someone would be expected to live based on the known or projected age-specific mortality rates they will experience during their lifetime. As cohort life expectancy takes account of actual or projected changes in mortality rates over time, it is regarded as a more appropriate measure of how long a person is expected to live in comparison to period life expectancy.

  • Completed family size (CFS)

    The average number of children that women born in particular years will have during the entire span of their childbearing years.

  • Components of population change

    The three types of events by which population size can change: births, deaths and migration.

  • Dependants

    Children aged under 16 years and individuals of state pension age and over.

  • Dependency ratio

    The number of dependants in a population per thousand persons of working age.

  • Fertility assumptions

    Assumptions about future fertility levels based on recent trends. For the purposes of the national population projections, fertility assumptions are formulated in terms of completed family size (CFS). Underlying the headline fertility indicators are age-specific fertility rates and an assumed sex ratio of 105 boys for every 100 girls born.

  • Marital status projections

    Projections which provide a breakdown of the population by legal marital status and (opposite sex co-residential) cohabitation. Marital status projections are presently available at England and Wales (combined) level only.

  • Migrant

    For the purpose of the population projections, a migrant is defined as an individual who changes their place of usual residence for a period of at least a year, so that the place of destination becomes the place of usual residence.

  • Migration assumptions

    Assumptions about future migration levels based on recent trends. For the national population projections, assumptions are made about levels of international and cross-border net migration. For subnational population projections, internal migration between regional and local areas is also considered.

  • Mortality assumptions

    Assumptions about future mortality levels based on recent trends. The mortality assumptions for the national population projections are formed by projecting age and sex specific mortality improvements. These are assumed to converge to target rates of mortality improvement 25 years into the projection period. Period life expectancy at birth is commonly used as a headline mortality assumption indicator.

  • National population projections

    National level population projections produced for the UK, its constituent countries, England and Wales (combined) and Great Britain. These projections are usually produced every two years.

  • Natural change

    The difference between the number of births and deaths over a particular period in a given area. If the number of births exceeds the number of deaths, there will be natural increase. If the number of deaths exceeds the number of births, there will be natural decrease. 

  • Net migration

    The difference between the number of in-migrants and out-migrants moving to and from a particular area over a given period. If the number of in-migrants exceeds the number of out-migrants, there will be net in-migration. If the number of out-migrants exceeds the number of in-migrants there will be net out-migration.

  • Pensionable-age dependency ratio

    The number of persons of state pension age and above per thousand persons of working age

  • Pensionable age population

    Individuals of state pension age and above. Between 2010 and 2020, state pension age will change from 65 years for men and 60 years for women, to 65 years for both sexes. Between 2024 and 2046, state pension age will increase in three stages from 65 years to 68 years for both sexes.

  • Period life expectancy

    The average number of years someone would be expected to live based on the age-specific mortality rates for the period and area in which they reside. This measure makes no allowance for any later actual or projected changes in mortality. In practice, mortality rates are likely to change in the future and people may live in other areas for at least some part of their lives. Therefore, period life expectancy does not give the number of years someone could actually expect to live.

  • Population projection

    An indication of the future population founded on trend-based assumptions of fertility, mortality and migration. Population projections are not forecasts. They do not attempt to predict the impact that new or future government policies, changing economic circumstances or other factors might have on demographic behaviour. They simply demonstrate the future population size and structure that would result if the separate assumptions about future fertility, mortality and migration levels were to be realised in practice.

  • Principal projection

    A population projection based on the fertility, mortality and migration assumptions considered to be the best at the time there are adopted. Hence the principal projection represents the most likely population outcome. May also be referred to as the main or central projection. 

  • Projection period

    The length of time a population projection spans. National population projections are published to 75 years ahead. Subnational population projections span a 25 year horizon. Population projections become increasingly uncertain the further they are carried forward, and particularly so for smaller geographic areas. Long-term figures should therefore be treated with caution.

  • Replacement level fertility

    The number of children needed to be born per woman for the population to replace itself from one generation to the next in the absence of migration. Replacement level fertility in the UK is about 2.075 children per woman.

  • Support ratio

    The number of persons of working age per persons of dependant age.

  • Total dependency ratio

    See Dependency ratio

  • Total fertility rate (TFR)

    The average number of children a group of women would have if they were to experience the age-specific fertility rates of the given year throughout their lifetime and survive to the end of their childbearing years. It is obtained by summing the age-specific fertility rates of the given year.

  • Variant projections

    To give users an indication of the inherent uncertainty of demographic behaviour, variant population projections are produced in addition to the principal projection. Variant projections are based on plausible alternative fertility, mortality and migration assumptions and illustrate the sensitivity of the projection results to changes in the underlying assumptions.

  • Working age population

    Individuals between 16 years and state pension age. Between 2010 and 2020, state pension age will change from 65 years for men and 60 years for women, to 65 years for both sexes. Between 2024 and 2046, state pension age will increase in three stages from 65 years to 68 years for both sexes.

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Contact Details

For statistical enquiries about this topic, please contact:

National Population Projections Unit

Email: projections@ons.gov.uk

Telephone: +44 (0) 1329 444652

National/Subnational Population Projections Room 2300 Office for National Statistics Segensworth Road Titchfield, Fareham PO15 5RR

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