Based on official population estimates and population projections, this briefing examines the impact of migration on recent and future UK demographic trends.
-
Key Points
- More than half (68%) of the increase in the UK population between 2005 and 2024 was due to the direct contribution of net migration. Since 2020, almost all of the growth in the population has come from net migration.
More… - Official figures projected that the UK’s population would grow from 69 million in 2025 to 72 million in 2049. Net migration accounted for 180% of this growth, because deaths were projected to outnumber births from 2030. Without international migration, the population would fall to 66 million by 2050.
More… - Each nation would experience population decline without future net migration, particularly Scotland and Wales, while the fall would be more modest in Northern Ireland.
More… - Net migration assumptions have been continually revised in the projections released since the mid-1990s, reflecting rising levels of net migration and the high uncertainty of migration forecasting.
More…
- More than half (68%) of the increase in the UK population between 2005 and 2024 was due to the direct contribution of net migration. Since 2020, almost all of the growth in the population has come from net migration.
-
Understanding the Policy
The UK does not have an explicit population policy. However, immigration policy decisions affecting people who come to the UK for work, study, family or humanitarian reasons all indirectly affect net migration and this in turn affects population growth. ... Click to read more.The level of net migration has been an important factor in immigration policy debates over the past 20 years. During the early 2010s, for example, the government had a target to reduce net migration to the UK “from the hundreds of thousands to the tens of thousands” – although this target was not met.
Immigration policy is not the only thing that affects net migration. Net migration can change even when policies stay the same. This is because many other factors affect who migrates to and from the UK, such as economic prospects in the UK and in countries of origin, changes in the global market for international study, or conflicts that produce refugees.
-
Understanding the Evidence
In the UK statistical system, long-term international migrants are defined as people who move into or out of the country for at least 12 months. Net migration is the balance between immigration and emigration over a given time period. ... Click to read more.In demographic terms, natural change – i.e., the difference between the number of births and deaths – measures the contribution of vital events to the dynamics of the population. Immigration and emigration contribute to population change both by altering the number of individuals in the country at a given time (direct contribution) and by affecting natural change (indirect contribution).
Population estimates
The Office for National Statistics (ONS) produces annual estimates of the resident population of England and Wales and estimates for the UK as a whole by collating data provided by the Northern Ireland Statistics and Research Agency (NISRA) and by the National Records for Scotland (NRS). The population at 30 June of a given year (stock) is obtained by annually ‘updating’ the most recent census population count with data on demographic events contributing to population change between these two dates (births, deaths and migration flows). Population estimates made between census years are revised retrospectively to provide a consistent series of population estimates over time. For example, the revised estimates for the period between the 2001 and 2011 censuses resulted in an adjustment of 497,500 (0.8%), primarily due to the underestimation of net migration in the previous series. Mid-year population estimates are also used as the base-year population of demographic projections.
Population projections
Population projections are calculations showing the future development of a population based on a set of assumptions about fertility, mortality and net migration. Official UK projections are usually revised every two years by updating base-year population estimates and assumptions underlying future demographic dynamics to reflect the latest available information. The COVID-19 pandemic disrupted the usual schedule and publications, however.
The most recent full set of projections – including variants to assess the impact of higher or lower net migration – used mid-2024 as the beginning of the projection period. In these projections, ONS provides a principal projection reflecting the ‘most likely’ population developments based on recently observed trends, as well as a number of variant projections intended to capture the uncertainty of the assumptions by showing the impact on population dynamics if one or more components of demographic change differ from the principal projection. This most recent principal projection assumes that net migration will level off at 230,000 per year from the year ending June 2027 onwards. This figure represents the estimated 10-year average net migration preceding the most recent projection. The net migration assumption was decreased from 340,000 per year in the January 2025 projections.
For comparative purposes, an important variant projection is ‘zero net migration’ (aka ‘natural change only’), which assumes migration inflows and outflows are equal at all ages throughout the projection period (with the same fertility and life expectancy as the principal projection). In this scenario, future population change is driven only by births and deaths. The comparison between the principal projection and the zero net migration variant allows one to assess the overall impact of net migration on population trends – i.e., including both the direct contribution and its impact on natural change.
Net migration exceeded natural change for most of the past two decades
Population estimates show that net migration was a major component of population growth over the past two decades, making up 68% of UK population growth from 2005 to 2024 (Figure 1). Natural change—i.e., the difference between the number of births and deaths—has declined since 2011, and fell into negative territory in 2023. As a result, net migration has accounted for 99% of population growth since 2020.
Figure 1
This retrospective analysis does not account for the contribution of past migration to natural change, mainly to births. The number of births over a given period is determined by the size and age structure of the female population and by fertility rates (i.e., the average number of children per woman in each age group). Migration affects both. That is, it affects the number of women of childbearing age and, if migrant women have different fertility patterns, the total fertility rate of the population as a whole.
ONS figures show that in 2024, 34% of births in England and Wales were to non-UK-born mothers. This is higher than the share of non-UK-born people in England and Wales, primarily because non-UK-born women are more likely to be of childbearing age. The estimated total fertility rate of foreign-born women living in England or Wales has declined over the past ten years to just below the ‘replacement rate’ (2.08) and stood at 2.03 in 2021, the latest year with available data. This, compared to 1.54 for UK-born women. Note that these figures include non-UK-born women regardless of how long they have lived in the UK.
The UK population is projected to grow to approximately 72.4 million by mid-2049
The most recent population figures from the Office for National Statistics projected that the UK population would grow to 72.4 million by mid-2049 (Figure 2). They assumed that net migration would average 230,000 over the long term (starting in mid-2027), similar to the levels of net migration seen during the 2010s. The projected rate of growth between mid-2024 and mid-2049 (4.5%, equivalent to 3.1 million people) is lower than the rate of growth seen in the previous 25 years, from mid-1999 to mid-2024 (18%, or 10.6 million people).
Figure 2
The projected population increase can be broken down into three components: the natural change that would occur if net migration was zero during the projection period; the direct contribution of post-2024 net migration (i.e., the number of individuals who will migrate to the UK minus the number of those who will leave the country); and the indirect contribution of post-2024 net migration (i.e., its effect on natural change).
In their principal projection, ONS projected that the UK population would grow by 2.3 million between 2025 and 2039 (Figure 2). Net migration accounted for 144% of this growth (3.3 million). In other words, the population would decline without net migration, because natural change (i.e., births minus deaths) was projected to be negative from 2026 onwards. The contribution of future net migration is higher if one also includes its impact on births and deaths in the calculation. Indeed, under the zero net migration variant, the UK population was projected to decline from mid-2025 onward.
However, ONS population projections are sensitive to different assumptions about net migration. The UK population was projected to be 3.5 million (or 5%) higher in 2039 under a scenario where net migration was 455,000 per year, compared to its central scenario, which assumed net migration of 230,000 per year.
Each UK nation would experience population decline without future net migration
Demographic and migration trends differ considerably across the four UK constituent nations, and future population scenarios reflect these differences. Under the ONS’s principal projection, the population of England would increase by 5% between 2024 and 2049, while Wales’s population would increase only marginally (0.3%). The populations of Scotland and Northern Ireland, by contrast, were projected to decline by 1% over the same period.
Net international migration was projected to make the largest contribution to population growth by 2049 in England, Scotland, and Northern Ireland, while cross-border migration from other parts of the UK was the biggest contributor in Wales (Figure 3). Each nation would experience population decline in the absence of net international migration—particularly Scotland and Wales, where deaths were projected to be significantly higher than births (relative to the size of their populations). In Northern Ireland, population decline would be more modest.
Figure 3
Evidence gaps and limitations
Population projections are not forecasts. They do not attempt to predict the impact of political, economic, social and cultural changes which may affect demographic patterns and trends, but rather are mechanical calculations that show the outcomes of sets of assumptions made for the three components of demographic change (fertility, mortality and migration). Projections are typically reliable for the short to medium term, with the exception of periods of shock such as the COVID-19 pandemic. Uncertainty increases the further the projections are carried forward in time, as any upward or downward changes in fertility, mortality and migration assumptions, compounded over time, can lead to significant variations in the projected population size and structure.
Future international migration is more difficult to project than fertility and mortality because migration flows are often affected by sudden changes in economic, social, or political factors, which are hard to predict or quantify, such as the sharp increase in net migration due in part to the war in Ukraine and high vacancy rates in the health and care sector. Migration assumptions are, therefore, the major source of uncertainty for long-term population projections, particularly in demographic regimes such as the UK, which are characterised by below-replacement fertility and low mortality levels. For more discussion on projections of future net migration, see the Migration Observatory briefing, Net migration to the UK.
In each revision of population projections, assumptions of future levels of fertility, mortality and migration are updated to reflect the most recently observed demographic trends. This has resulted in sizeable revisions in different sets of population projections released, particularly throughout the 1990s and 2000s. In the 1994-based principal projection, for example, net migration was assumed to return to zero in the long term, reflecting the levels of net migration observed during the 1980s and early 1990s. As a result, the size of the UK population was projected to peak at 61 million in 2023 and then start to decrease (Figure 4).
Figure 4
In the subsequent projections, upward revisions of assumed net migration levels were introduced to reflect the rapid increase in migration flows to and from the UK. As a result, projected population growth rates have also increased. In the 2024-based revision, published in April 2026, the projected size of the UK population in 2031 was around 10 million higher than in projections produced in the mid-1990s.
The ONS does not attempt to model the impact of policy changes when setting its migration assumptions. Therefore, its population projections do not reflect a prediction about how current policy will affect future net migration.
Further reading
- NISRA, 2025. 2024 Mid-Year Population Estimates for Areas within Northern Ireland. Belfast: Northern Ireland Statistics and Research Agency. Available online.
- NRS, 2024. Mid-2024 population estimates for Scotland. Edinburgh: National Records of Scotland. Available online.
- ONS, 2025. Population estimates for England and Wales: mid-2024. Newport: Office for National Statistics. Available online.
- ONS, 2026. National population projections: 2024-based. Newport: Office for National Statistics. Available online
-
Media Coverage
-
Financial Times (27 May 2016)
Soaring population driven only in part by migrants
-
Financial Times (27 May 2016)
