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Frequently Asked Questions, 2010-Based National Population Projections This product is designated as National Statistics

Released: 26 October 2011 Download PDF


This report provides frequently asked questions on national population projections in general as well as more specifically on the 2010-based release.

Generic national population projections FAQs

What are the national population projections?

National population projections are prepared by the Office for National Statistics (ONS) on behalf of the National Statistician and the Registrars General for Scotland and Northern Ireland. They are produced every two years and provide projections of the future size and age structure of the population for the UK and its constituent countries. The national population projections are National Statistics, which means that they undergo regular quality assurance reviews and are produced free from political interference.

How are the projections produced?

The national population projections are based on the latest available mid-year population estimate and a set of demographic assumptions about future fertility, mortality and migration based on analysis of trends and expert advice. They are produced using the internationally accepted cohort component methodology. This method accounts for changes which increase or decrease the population (births, deaths and net migration) and models the effect of these changes and the passage of time on the age structure of the population.

Do the projections take government policies into account?

The national population projections are not forecasts and do not attempt to predict the impact that future government policies, changing economic circumstances or other factors (whether in the UK or overseas) might have on demographic behaviour. They simply provide the population levels and age structure that would result if the underlying assumptions about future fertility, mortality and migration were to be realised.

What population is covered by the projections?

Projections are made of the usually resident population of the UK and its constituent countries, whatever their nationality. The usually resident population includes all long-term international migrants (people changing their country of usual residence for at least one year). However, the usually resident population does not include short-term migrants who come to or leave the UK for less than a year.

How are the assumptions underlying the projections agreed?

The assumptions about future levels of fertility, mortality and net migration are agreed in liaison with the devolved administrations (namely National Records of Scotland (NRS), the Northern Ireland Statistics and Research Agency (NISRA) and the Statistical Directorate of the Welsh Government (WG)), following consultation with key users of projections in each country and advice from an expert academic advisory panel. This advisory panel is convened by the British Society for Population Studies (BSPS); details of the membership of the panel and minutes of meetings are published in Appendix A of the background and methodology report on the 2010-based projections.

Why are the national population projections produced?

The main purpose of the national population projections is to provide an estimate of the future population of the UK (and its constituent countries) as a common framework for use in national planning in a number of different fields.

Who produces the projections?

The Government Actuary's Department (GAD) was responsible for the production of the official national population projections from 1954 to 2006. Responsibility for production of the projections transferred from GAD to ONS on 31 January 2006. The first set of national population projections produced by ONS were the 2006-based projections published in October 2007.

Who are the main users of the projections, and what are they used for?

The national population projections are widely used across government for planning purposes. Examples include:

  • The Office for Budget Responsibility (OBR) use the projections as a key input to their long-term fiscal projections published in the fiscal sustainability report.

  • The Department for Work and Pensions (DWP) use the projections extensively to produce forecasts of expenditure for benefits and pensions and as a key input for analysis on policy areas such as extending working lives.

  • The Department for Education use the projections as the basis for their projections of future school pupil numbers.

The national population projections also provide the base for other products such as subnational population projections and household projections, which are widely used for resource allocation and planning.

Why do you produce variant projections?

Projections are uncertain and becoming increasingly so the further they are carried forward in time. It is vital that users of population projections, especially those with long-term planning horizons, take account of this uncertainty in their planning.  In addition to the principal (or central) projection, variant projections are therefore also published based on alternative, but still plausible, assumptions. These variant projections provide an indication of uncertainty by allowing users to consider the impact upon the population if future fertility, mortality and migration differ from the assumptions made for the principal projection. The publication of variant projections is an internationally recognised method for illustrating the uncertainty associated with population projections.

How far ahead do the projections go?

Projections are uncertain and become increasingly so the further they are carried forward in time. For this reason, analysis of the projection results mainly focuses upon the first 10 or 25 years of the projection period, which corresponds with the planning horizons of the majority of users of the projections, whilst recognising that uncertainty will be greater over a 25 year period. However, some key users require projections over a longer period for modelling purposes, and in accordance with the government's transparency agenda, results for the 2010-based projections have been published for up to 100 years ahead. However, caution should be used when interpreting these longer-term projections as projections become increasingly uncertain the further into the future they go. Variant projections are also available to aid interpretation of the uncertainty.

2010-based national population projections FAQs

What is the latest set of national population projections?

The latest set of national population projections is the 2010-based projections published by ONS on 26 October 2011. They are based on the estimated population at the middle of 2010. The principal (central) projection is based on assumptions considered to best reflect demographic patterns at the time they were adopted. However, due to the inherent uncertainty of demographic behaviour, ONS also produce a number of variant population projections, based on alternative, but still plausible, assumptions of future fertility, mortality and migration. Nine variant projections are published alongside the principal projections on 26 October 2011, and a further 11 variant projections will be published on 23 November 2011.

Where can I find the latest projections?

The latest national population projections are available on the ONS website. Detailed information on the assumptions underlying the projections and the methodology used to produce the projections can be found in the reports and an interactive table download tool is also available. The 2010-based National Population Projections Reference Volume (PP2, No28) will be published in Spring 2012.

What are the findings of the 2010-based projections?

ONS produces a principal (central) projection and also a number of variant projections based on alternative assumptions. The 2010-based principal population projection for the UK projects that the population will increase by 4.9 million over the next ten years from 62.3 million at mid-2010 to 67.2 million at mid-2020, an annual average rate of growth of 0.8 per cent which is comparable to the increases seen around the mid-1960s baby boom. It is projected that the UK population will be 73.2 million at mid-2035, a total increase of 10.9 million over the next 25 years. More detailed commentary is available in the Statistical Bulletin and the 2010-based National Population Projections Reference Volume (PP2, No28) will be published in Spring 2012.

What are the assumptions underlying the latest projections?

ONS produces a principal (central) projection and also a number of variant projections based on alternative assumptions. The 2010-based principal population projection for the UK assumes:

  • a long-term average completed family size of 1.84 children per woman,

  • life expectancy at birth in 2035 of 83.3 years for men and 87.0 years for women, with constant rates of mortality improvement assumed thereafter,

  • long-term annual net migration to the UK of +200,000 per year.

The variant projections illustrate future population change under alternative scenarios. The assumptions underlying these variant projections are available as part of this release.

Is the projected growth in the population due to births or migration?

Of the 10.9 million projected increase in the UK population over the next 25 years, 53 per cent is projected natural increase (more births than deaths) and 47 per cent is projected net migration. However, future numbers of births and deaths are themselves partly dependent on future migration. Taking this into account, just over two-thirds (68 per cent) of projected population growth between 2010 and 2035 is expected to be either directly or indirectly due to future net migration.

Do the assumptions about future migration reflect the latest patterns of international migration?

The 2010-based principal projection assumes that levels of net migration to the UK will be +200,000 per year from 2016/17 onwards which is broadly in line with average migration over recent years. Provisional international migration data for 2010, published by ONS on 25 August 2011, was used to inform the assumption for the first year of the projection. From 2011/12 an allowance has been made for assumed declining levels of net in-migration from the A8 and A2 accession countries that joined the EU in May 2004 and January 2007[1]. This allowance is +40,000 in 2011/12 before reducing to zero for 2016/17 onwards, with migration inflows and outflows to/from the accession countries assumed to balance in the long-term.

What do the latest projections show regarding population ageing?

The population is projected to rise most quickly for the oldest age groups. The number of people aged 85 and over is projected to increase by 35 per cent over the next 10 years, rising from 1.4 million in 2010 to 1.9 million in 2020, and to more than double over the next 25 years reaching 3.5 million by 2035. Despite the forthcoming increases in State Pension Age, the ratio of working age people to each person of state pensionable age is projected to decline from 3.2 in 2010 to 2.9 in 2035.

How do the 2010-based projections compare with previous projections?

Overall the projected future population size is higher than that in that in the previous (2008-based) projections. This is mainly due to differences in the assumptions of future fertility, mortality and migration.

Compared to the 2008-based projections, the long-term fertility assumption has remained the same. However higher fertility levels are assumed in the short-term, with the assumed UK fertility rates set to increase from current levels to a high of 2.02 in 2013 before decreasing to the long-term assumption of 1.84 by 2027. These short-term assumptions are very different to those used in the 2008-based projections which assumed a decreasing fertility rate and reached the long-term within five years. The 2010-based assumptions are higher and stay higher for longer reflecting the current relatively high trends in fertility. The fertility assumptions form part of this release.

In general the annual rates of mortality improvement in the longer-term have been increased from 1% to 1.2%. However this is counterbalanced by the age-specific mortality rates for 2010 being assumed to be higher and the rates of mortality improvement between 2010 and 2011 assumed to be lower at many ages below 90 compared to those projected for the same period in the 2008-based projections. This leads to projected period life expectancies at birth for the year 2035 are around 0.1 years lower than in the previous projections for males and 0.1 to 0.3 years lower for females. The mortality assumptions form part of this release.

The assumed net migration is higher in the short and long-term than that assumed for the 2008-based projections.

How accurate have past projections been?

ONS published an analysis of the past accuracy of national population projections in 2007 in Population Trends 128 (868.6 Kb Pdf) . This analysis considered the 1955-based to 2004-based projections and compared these projections with the latest estimates of the UK population up to mid-2005. The analysis found that the mean absolute error of the projected total UK population 20 years ahead was about 2.5 per cent overall (when considering 1955-based to 1985-based projections), and lower than 2 per cent when just the most recent (1975-based to 1985-based) projections were considered. This would correspond to around 1.4 to 1.8 million people (2.0 to 2.5 per cent mean absolute error calculated on the 2010-based principal projection for 2030). The largest differences between projected and actual populations were found to be for the youngest and oldest ages, while projections of the working age population were found to be comparatively accurate.

Why were the 1955-based and 1965-based so inaccurate?

The 1955-based national population projections, produced prior to the 1960s baby-boom, projected the lowest future population sizes of any official projection. The projected population for 1995 (40 years ahead) was 53 million, some five million lower than the population estimate for mid-1995. In contrast, the 1965-based projections, produced at the height of the 1960s baby-boom, projected the highest future population sizes - the projected population for 2001 (36 years ahead) was 75 million, some 16 million higher than the population estimate for mid-2001. This illustrates the difficulty in projecting the population during periods of demographic change, and the importance of bearing in mind the uncertainty of projections, particularly over longer periods of time.

When is the UK population projected to reach 70 million, and why is this population level of significance?

According to the 2010-based principal projection, the UK population will reach 70 million in 2027, slightly earlier than the date of 2029 projected by the 2008-based projections and 2028 projected by the 2006-based projections. A population level of 70 million is of no special demographic significance, although some customers of population statistics will inevitably be interested in when and how fast the population might reach numerical milestones such as 50 million, 60 million and 70 million. The UK population is estimated to have reached 50 million in 1948 and 60 million in 2005. It is therefore projected that the population will rise from 60 to 70 million over a period of 22 years, compared to the 57 years over which it rose from 50 to 60 million.

When will all the variant projections be available?

The release on 26 October 2011 covered the main (principal) 2010-based projections and nine key variant projections based on alternative, but still plausible, assumptions. On 23 November 2011, ONS will release a further 11 variant projections that illustrate additional alternative scenarios to supplement the projections released in October. This November release will form part of the overall release of the 2010-based national population projections, the main results of which are described in the Statistical Bulletin and News Release published on 26 October.

Will the UK population go on growing forever?

Under the principal projection assumptions, the size of the UK population is projected to continue increasing over the projection period. However, projections are uncertain and become increasingly so the further they are carried forward. For example, in the high and low migration variant projections, which assume alternative but still plausible levels of future net migration, the total population of the UK at 2060 would be around 4.3 million higher or lower than in the principal projection.

Are projections for areas within the UK available?

The 2010-based national population projection release includes projections for Great Britain, England & Wales, England, Wales, Scotland and Northern Ireland as well as the UK. Projections for subnational areas for England produced by ONS are published typically about six months later than the national projections. Subnational projections for Wales, Scotland and Northern Ireland are produced by the WG, NRS and NISRA respectively.

How does the future changes to the UK population compare with other countries in Europe?

A comparison of population projections across Europe is included in the Statistical Bulletin.

Notes for 2010-based national population projections FAQs

  1. The A8 countries that joined the EU in May 2004 are the Czech Republic, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia. The A2 countries that joined the EU in January 2007 are Bulgaria and Romania.

Background notes

  1. Details of the policy governing the release of new data are available by visiting or from the Media Relations Office email:

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

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