Provisional long-term international migration estimates: technical user guide

This guide provides detailed methodological information related to the data sources and methods used to estimate long-term international migration, including estimates for EU, non-EU and British Nationals. It can be referenced by technical users when using our statistics and will be updated following any method changes.

About our estimates

Our Long-term international migration (LTIM) estimates are currently published twice a year, at the end of May and at the end of November. We publish estimates of immigration, emigration and net migration for non-EU, EU and British nationals, as well as further nationality breakdowns for immigration into the UK. Our latest estimates currently use different data sources and methods for each nationality grouping.

We define a long-term international migrant (applying the United Nations definition) as someone who changes their country of usual residence for 12 months or more, so that the destination country effectively becomes the country of usual residence. Our estimates are calculated for international migration within 12-month reference periods, for example year ending (YE) December 2023 covers international migration to and from the UK from 1 January 2023 to 31 December 2023.

LTIM statistics estimate migration to and from the UK using administrative data, supported by surveys and statistical modelling. We are transforming the way we produce migration statistics to make greater use of administrative data and have reclassified these as official statistics in development, in line with the Office for Statistics Regulation guidance. We aim for these statistics to be classified as Accredited official statistics in 2025.

The latest available data for long-term international migration provide consistent migration estimates from 2012 to present. The latest published three data points are provisional. While we know how many have arrived or left, when producing provisional estimates (the latest of which is only five months after the reference period) we apply assumptions and adjustments based on historical data to account for not having 12 months of information on travel patterns to determine if a person is a long-term migrant. These provisional estimates are updated when more data become available. For a preliminary estimate of uncertainty that arises from these adjustments, see our methodology, Measuring uncertainty in international migration estimates.

Non-EU migration refers to the migration of people who do not hold British or EU nationality.

Data source

To produce our estimates of non-EU international migration, we use Home Office Borders and Immigration (HOBI) data. These are derived from a linked database that combines data from Home Office systems to build travel histories that consist of an individual’s travel into or out of the UK, and data relating to their immigration status. For more information, see our article, Long-term international migration: quality assuring administrative data.

Method

Organising the data

1. The HOBI data are filtered based on nationality to only include non-European Economic Area (EEA) nationals. Nationality is derived from an individual’s most recent priority biographic record, for example, the latest passport swipe, their immigration record, or Advanced Passenger Information.
2. Those on Visit visas are filtered out as they are only eligible to stay in the UK for up to six months at a time.
3. Visa periods are constructed by linking together consecutive or concurrent visas. Short-term visas can be linked with long-term visas when forming visa periods. The most recent visa period is extended with visas not yet travelled on. Where there is a gap of more than seven days between visas, a new visa period is started. If an individual has a record of long-term travel outside the UK and has left for more than 12 months during a visa period, they will be counted as an emigrant and a new visa period is started on their next arrival.
4. The first arrival and last departure dates are identified using travel histories within a visa period. These are used as an approximation for length of stay in the UK. To estimate long-term international migration, this total length of stay must be over one year (365 days).
5. If either the first arrival or last departure information is missing (but not both), and there is evidence of future travel to or from the UK during their visa, visa start, or end dates are used as a proxy.
6. Any trips abroad over the course of a visa period are excluded when calculating total length of stay.

Creating the immigration and emigration estimates

1. After identifying the first arrival and last departure within a visa period, previous visa periods are examined to determine if this is a new long-term immigration or someone who has previously been in the country. If no presence in the country is identified during the 12 months preceding first arrival on a given visa, or the previous stay was for less than 12 months, this is considered a new long-term immigration. We exclude individuals from the immigration estimates if they have a missing first arrival and are either young children or travelling on in-country 10 year family/private life visas.
2. For individuals whose first arrival occurred within the most recent 12 months (and therefore we are unable to say whether they will become a long-term migrant), their visa end date is used as a proxy for a future departure date. All individuals in this group are therefore initially counted as long-term immigrants.
3. Some individuals leave before their visa end date and therefore are not long-term immigrants. An early leaver adjustment is applied to account for not having data available showing evidence of 12 months in or out of the country, broken down by each visa type.
4. To estimate emigration, previous long-term immigrations to the UK who have a departure from the UK during the reference period are identified. We record them as a long-term emigration if they do not return to the UK within 12 months, or if they only return for a short-term stay of less than 12 months.
5. As this method is dependent on having a completed visa period to identify a departure, an early exits adjustment is applied for the most recent 12 months of the data extract to include individuals in our emigration estimate that have left the UK, not subsequently returned, and who have up to three months left on their visa.
6. For years prior to this 12-month period, the early exits adjustment includes individuals in the emigration estimate who have left the UK and not returned within 12 months or more, but still have a valid visa.
7. For the most recent 12 months, an emigration re-arrivals adjustment is applied to account for not having enough data to identify whether an individual, who is observed to have departed the UK, will become a long-term emigrant, or subsequently return within the next 12 months.
8. Reason for migration is estimated using the first visa type they were granted to enter the UK.

Assumptions and adjustments to produce provisional non-EU migration estimates

Assumptions included in the processing

Unmatched leave

Some individuals within HOBI data have travel information with no matched visa. These are either those with short visits which do not require a visa or those where the system has not matched the travel and visa information together. Those with visa information are linked in our system and included in our estimates and we remove those who should not be included.

Removing non-visa nationality events

HOBI data contain travel events where individuals have travelled to the UK without a visa as there are certain countries where travel is allowed for up to six months without a visa e.g. USA, Australia, Mexico. Travel events within this category cannot represent an individual who has stayed for 12 months so all travel events within this category are excluded from immigration estimates.

Removing Visit visas

A Visit visa allows an individual to stay in the UK for a maximum of six months. Therefore, all instances of Visit visas are excluded from the estimates as it does not permit an individual to be within the UK for 12 months or more.

Using visa start and end dates as a proxy arrival or departure date

If either the first arrival or last departure information is missing in HOBI data and there is evidence of future travel into or out of the UK during their visa, visa start, or end dates are used as a proxy. These dates can be missing if an individual travelled through the Common Travel Area or if there are instances of travel that have not successfully matched to a visa. If both the first arrival and last departure are missing, and there is no evidence of other travel information that we can use as proxy, we assume that the individual has not travelled to the UK or arrived on their visa.

Visa end dates beyond extract date

HOBI data are provided quarterly, spanning five years (the extract period). If an individual has a departure within the extract period but has a visa end date beyond the extract period, they have permission to return to the UK on this visa. Therefore, we use their visa end date as a proxy for a future departure date. We include these individuals within the immigration estimate, even if they have a departure within 12 months of their first arrival, until their visa end date has been reached and it can be confirmed that they have stayed in the UK for fewer than 12 months.

Adjustments to produce provisional estimates of migration

Immigration early leaver adjustment

For individuals whose first arrival occurred within the 12 months before the end of the data extract, not enough time has passed to identify a stay of 12 months or more. To account for this, the percentage of people who did not actually stay long-term for the previous year is used as a proxy. This percentage is applied to the final immigration estimate by reason for migration, nationality and age, as our research has shown that different groups exhibit different behaviours. This adjustment is frequently updated so for the most up to date assumptions, see our International migration research, progress update series.

Emigration early exits adjustment

The “first arrival, last departure” emigration method is dependent on having a completed visa period within which to identify a last departure. Anyone who has valid leave to remain in the UK (meaning that their visa has not expired) at the end of the reference period is not counted as an emigrant, even if they left the UK over a year ago, as they could potentially return to the UK.

For the most recent 12-month reference period, we do not have enough data to see if an individual has left for 12 months or more and not returned. Therefore, we include individuals in the emigration estimate who have left the UK, not subsequently returned, and who have up to three months remaining on their visa.

For years prior to this period, when updating our estimates, we include individuals in the emigration estimate who have left the UK and not returned within 12 months or more, but still have a valid visa.

Any individuals that are assumed to be an early exit are removed from the immigration estimate if their length of stay is fewer than 12 months.

Emigration re-arrivals adjustment

For the most recent data, we do not have enough data to identify whether an individual, who is observed to have departed the UK, will become a long-term emigrant, or subsequently return within the next 12 months and therefore should not be classified as a long-term emigrant. This could happen if someone were to go abroad on holiday towards the end of their current visa but return and switch to a new visa.

Similarly to the early leaver adjustment, we take an average of how many departees in a reference period subsequently return within 12 months using data from 2021, 2022 and 2023, which is double weighted to better reflect current trends. We remove this percentage from the most recent emigration estimate.

EU+ migration refers to the migration of people who hold EU nationality. This is the sum of EU14, EU8, EU2, Norway, Iceland, Liechtenstein, and Switzerland, plus Malta, Cyprus and Croatia (from 1 July 2013).

Data source

Our latest methods to estimate the migration of EU+ nationals creates admin-based migration estimates from the Registration and Population Interaction Database (RAPID) which covers everyone with a National Insurance number (NINo), and adjustments are implemented for those without. RAPID is created by the Department for Work and Pensions (DWP) to provide a single view of citizens' interactions across the breadth of systems in DWP, HM Revenue and Customs (HMRC), and local authorities via Housing Benefit.

RAPID data are supplied to the Office for National Statistics annually in Quarter 3 (July to Sept) for the previous tax year. We have worked with DWP to create a version of RAPID including only non-UK nationals (RAPID Migration Dataset) using information from the Migrant Worker Scan, which identifies all non-UK nationals registering for a NiNo from 1975 onwards. For more information, please see Long-term international migration: quality assuring administrative data.

Method

Organising the data

1. All separate tax year data files in the RAPID Migration dataset are amalgamated into a single dataset holding all tax years from FY2010/11, or for those arriving after 2010, the tax year of their first arrival.
2. A person’s “activity” is identified by calculating the length of each interaction with DWP, HMRC and the local authority systems in the tax year (for example, the payment of income tax or the receipt of housing benefit). Activities that cannot occur at the same time, such as employment and an out of work benefit, are added together. For someone to be classed as resident by DWP, they must have at least one week of interactions with tax or benefit systems and have at least one piece of geographical data showing they have a UK address.
3. The data is filtered to only include EU+ nationals. This includes those on the EU Settlement Scheme.

Creating the immigration and emigration estimates

1. Two types of sustained long-term activity that most closely align with the UN definition of a long-term migrant are used to identify migration to the UK. These two categories make up the largest proportion of long-term arrivals in the RAPID data (over 90%).

Category 1: the number of weeks of activity in the registration year (the year that an individual registers for a NINo) and registration year plus 1 are a total of at least 52 weeks (minimum 52 weeks out of the 104 weeks in a two-year period). This suggests they are resident for 52 weeks or more over that two-year period. It is assumed that the 52 weeks of activity over the two-year period are consecutive. However, the RAPID data does not show when in the tax year this activity was, rather how many weeks of activity. Even if this activity is not consecutive, we assume that the person is resident across that whole period. Category 1 arrivals make up 80% of all EU long-term arrivals in the RAPID data.

Category 2: the number of weeks of activity in the period between arrival and registration, and the duration of activities in the registration year and registration year plus 1 are a total of 52 weeks or more. This suggests they are resident for 52 weeks or more over that period. In some instances, there can be a long lag between an individual’s self-reported date of arrival and their registration for a NINo. There are many reasons someone may not need a NINo when they first arrive, such as being a student, but then later register for a NINo to work. Category 2 arrivals make up 10% of EU+ arrivals in the RAPID data.

2. These categories are applied in a hierarchical order. If any EU nationals do not fit into either of these categories, they are not included in our estimates.

3. To estimate long-term emigration, individuals who no longer have any activity in the RAPID data over an entire tax year are assumed to be no longer resident in the UK and are therefore counted as a long-term emigrant.

4. Re-arrivals are estimated by applying the Category 1 rules. Anyone with an extended period of inactivity and counted as a long-term emigrant in step 3, and then has a subsequent period of activity will be counted as a re-arrival.

5. Our EU+ estimates are then adjusted to account for the populations who have less or no interaction with the source datasets. These include adjustments for international migrants that have recently arrived or departed the UK, students who are not working or claiming benefits and children under 16 years of age.

6. Temporal disaggregation (Fernandez method PDF, 2.3MB), which uses a regression approach to look for a relationship between two datasets, is used to breakdown the annual RAPID EU+ data into monthly data and then reaggregate to year ending quarterly data.

7. Our EU+ estimates are forecasted for the three- or nine-month period, which the latest version of the data does not cover, based on signals and trends in the International Passenger Survey (IPS). While we have acknowledged the long-standing issues with IPS measuring the levels of migration, the IPS seasonality and trend of migration flows are useful for the RAPID forecasting.

8. The self-declared reason for coming to the UK from the IPS is used to estimate reason for migration. The Economic Commission for Europe’s report (PDF, 370KB) states that the self-reported reason for migration does not always match the reason they have been granted permission to enter. Users should therefore exercise caution when comparing the reasons for migration of non-EU+ with EU+ and British nationals.

Assumptions and adjustments to produce provisional EU migration estimates

Assumptions included in the processing

Total activity assumption

Information contained within the RAPID data only specifies the total number of weeks of interactions within each tax year and does not specify when or whether this activity is continuous. However, we assume the total activity estimated to be sufficient to indicate long-term presence in the UK.

Adjustments to address coverage gaps

Students who may be excluded if they are not working or claiming benefits

Migrants who come to the UK with the sole purpose of studying may not be in RAPID. They will not be included if either; they do not hold a NINo, or if they do hold a NINo, they may not be identified as resident in the UK, if they do not undertake any activity that verifies residency (for example, working). Students who do work alongside their studies may not have enough activity to class them as a long-term migrant if they only work during term time.

To account for this undercoverage, we use alternative data to tell us about international students. The total number of students is identified using the most recent version of Higher Education Statistics Agency (HESA) data. Historical HESA data are linked with HMRC Pay as You Earn Real Time Information data using the Demographic Index (PDF, 550KB) to better understand how many international students are in employment alongside their studies. We then adjust our estimates to include the proportion of students that do not show employment activity and are therefore not included in our initial estimates. See International migration research, progress update: November 2022 for further information.

Children aged under 16 years

Children who arrive into the UK do not need to register for a NINo so are not included in RAPID data. While RAPID includes Child Benefit data, it does not provide nationality and is therefore not suitable for the analysis of migration to or from the UK.

An adult-to-child ratio is derived from the International Passenger Survey (IPS) for the same reference year as RAPID. This ratio is the proportion of EU nationals aged under 17 years compared to those aged 17 to 64 years and is calculated separately for immigration and emigration. Where IPS data are not available (2020), we apply a three-year average ratio (2018, 2019 and 2021). The ratio is used to identify the number of children to add to the RAPID immigration and emigration estimates.

Adjustments to produce provisional estimates

Inflow and outflow adjustment

International migrants that have recently arrived or departed the UK will not necessarily meet the 12-month residency rule of the UN definition of a long-term international migrant (LTIM). We adjust the estimates from the two most recent tax years to account for this. We calculate the proportion of migrants that have historically become LTIM, both immigrants and emigrants, and apply this to the number of arrivals and departures in the most recent tax years.

Our British national estimates include the migration of individuals who hold the following types of British (English, Scottish, Welsh, and Northern Irish) nationality:

• British citizenship
• British Overseas Territories citizen
• British overseas citizen
• British subject
• British protected person

Data source

Our research into British nationals is ongoing. The complexity associated with identifying British migrants in administrative data means we cannot use such data at this time.

Instead, we use International Passenger Survey (IPS) data. The IPS conducts face-to-face interviews with a sample of passengers as they pass through major UK airports, sea routes and the Channel Tunnel. More information on the survey methodology can be found in our IPS Quality and Methodology Information report. It is important to note that these data are intentions-based, and our research has shown that intentions do not always reflect actual behaviour. Further details can be found in Estimating UK international migration: 2012 to 2021.

Method

Organising the data

1. Every quarter, we receive provisionally weighted IPS data for the interviews conducted within the previous three-month period.
2. The data are validated, missing values are imputed, and any identified errors are manually corrected.
3. A simplified and processed version of the data is exported which contains information on individuals meeting the definition of a long-term migrant – those that expressed intentions to stay or leave the UK for at least 12 months. Nationality is self-reported by individuals when interviewed.

Creating the immigration and emigration estimates

1. The data are loaded into tabulation software which is used to produce our estimates of British national immigration, emigration, and net migration.
2. British national (Overseas) arrivals from Hong Kong are removed from our immigration estimates to prevent double counting as they are included within our non-EU estimates.
3. The self-declared reason for coming to the UK is used to estimate reason for migration. The Economic Commission for Europe’s report (PDF, 370KB) states that the self-reported reason for migration does not always match the reason they have been granted permission to enter. Users should therefore exercise caution when comparing breakdowns of non-EU with EU and British nationals.

We use data published by the Home Office to add the total number of asylum applicants and resettlement scheme arrivals to the international migration estimate. We do not include arrivals from the Ukraine Schemes and British nationals (Overseas) as these groups are already included in the non-EU estimates.

Adjustments to produce asylum and resettled refugees estimates

We make an adjustment to address potential double counting by linking asylum applications data to visa data to identify asylum applicants who had previously entered on a visa, and are already counted as a long-term migrant, and applied for asylum before the end of their visa. We remove these from our immigration estimates.

We also link the asylum applications data to asylum returns data to remove applicants from the emigration estimate who were returned within one year of raising their application. No adjustment is applied in the last four quarters of the data to account for returns that have not yet occurred within a year.

Finally, we identify records in the Home Office Borders and Immigration data for those with a visa expiring after their application was raised to ensure that they are not included in the non-EU emigration estimates.

To ensure that we continue to provide accurate and timely statistics that meet users' needs, we have been improving our methods to move away from survey-based data to using administrative data, as explained in our Improving international migration statistics using administrative data article.

The different methods we have used to calculate international migration, developed since April 2021, are summarised in our Long-term international migration estimates methodology.

For a more detailed explanation of the research we have been undertaking through our migration statistics transformation programme to develop admin-based migration estimates (ABMEs), see our international migration research, progress update articles.

Rounding

All estimates within the data are rounded to the nearest thousand because of the provisional nature of our statistics. Therefore, totals may not add exactly. Percentages are rounded to the nearest whole percentage.

Revisions

Timely, published estimates are provisional estimates, which give an initial indicator of population or migration based on early data and assumptions about people’s migration status, based on past behaviour. These are updated when more data relating to people who arrive in the reference period and whether they stay in the UK for at least 12 months become available. In statistical outputs, we refer to the planned updates resulting from improvements to data or methods as revisions. Our approach to revisions is guided by international best practice and is consistent with our Guide to statistical revisions. Further details can be found in our Revisions policy.

Details about the revisions made can be found in section 8 of our long-term international migration bulletins.

These types of planned revisions should not be confused with errors in released statistics, which are genuine mistakes. Despite our best efforts and quality control procedures, mistakes can happen. When they do, corrections are made in a timely manner, announced and clearly explained to users in line with the Code of Practice for Official Statistics.

Administrative data

Collections of data maintained for administrative reasons, for example, registrations, transactions, or record keeping. They are used for operational purposes and their statistical use is secondary. These sources are typically managed by other government bodies.

Asylum applicants

Asylum applicant (also referred to as "asylum seeker") is someone who makes a claim to be recognised as a refugee under the Refugee Convention.

"Asylum" estimates in this bulletin refer to the long-term international migration of people who have applied (that is, made a claim) for asylum in the UK.

An asylum-related return is one where there has been an asylum claim at some stage prior to the return. For more information on this, see the User Guide to Home Office Immigration Statistics.

British national

A British national is person who holds a type of British (English, Scottish, Welsh, and Northern Irish) nationality. There are six different types of British nationality:

• British citizenship
• British Overseas Territories citizen
• British overseas citizen
• British subject
• British national (Overseas)
• British protected person

For the purposes of our estimates, we have treated British national (Overseas) (BN(O)) as a separate category.

British national (overseas) (BN(O))

Someone who was a British Overseas Territories citizen by connection with Hong Kong lost that citizenship on 30 June 1997, when sovereignty returned to China. However, such a person was able to register as a British national (overseas) (BN(O)) before 1 July 1997. For more information, see the Types of British nationality guide on GOV.UK.

On 31 January 2021, the UK launched a bespoke immigration route for British nationals overseas (BN(O)) status holders and their families from Hong Kong.

EEA

The EEA includes EU countries and also Iceland, Liechtenstein and Norway.

EU

EU is the sum of EU14, EU8, and EU2, plus Malta, Cyprus and Croatia (from 1 July 2013). British nationals are not included in these numbers.

EU2

EU2 is Romania and Bulgaria.

EU8

EU8 is Czechia, Estonia, Hungary, Latvia, Lithuania, Poland, Slovakia and Slovenia.

EU14

EU14 is Austria, Belgium, Denmark, Finland, France, Germany, Greece, Republic of Ireland, Italy, Luxembourg, the Netherlands, Portugal, Spain and Sweden.

Other EU

Other EU is Malta, Cyprus and Croatia (from 2013).

Home Office Borders and Immigration data

A linked database that combines data from Home Office (HO) systems to build travel histories that consist of an individual's travel into or out of the UK, together with data relating to their immigration status. This system has data for all non-European Economic Area (non-EEA) visa holders.

International Passenger Survey (IPS)

Our International Passenger Survey (IPS) collects information about passengers entering and leaving the UK and has been running continuously since 1961. The IPS was resumed in January 2021, after being suspended since March 2020 because of the coronavirus (COVID-19) pandemic. Currently, we use it for our British national estimates and for providing information on reason for migration.

Long-term international migration

Long-term international migration (LTIM) statistics estimate the flow (or movement) of migrants to and from the UK. This bulletin uses the UN-recommended definition of a long-term international migrant. It is defined as "A person who moves to a country other than that of his or her usual residence for a period of at least a year (12 months), so that the country of destination effectively becomes his or her new country of usual residence."

A “long-term international immigrant” refers to a person who has moved to the UK from abroad for a period of at least a year.

A “long-term international emigrant” in this bulletin refers to a person who has left the UK to go to another country for a period of at least a year.

Nationality

Nationality of a country is a legal status that usually gives a person a particular set of rights relating to that country.

Net migration

Net migration is the difference between the number of people coming to live in the UK (immigration) and the number of people leaving to live elsewhere (emigration). When more people are arriving in the UK than leaving, net migration is above zero and so adds to the non-UK population.

Non-EEA

Non-EEA is the rest of the world excluding EEA countries and the United Kingdom.

Non-EU

Non-EU is the sum of the rest of the world. British nationals are excluded from these numbers.

Registration and Population Interaction Database (RAPID)

Registration and Population Interaction Database (RAPID) is a database created by the Department for Work and Pensions. It provides a single coherent view of interactions across the breadth of benefits and earnings datasets for anyone with a National Insurance number (NINo).

Ukraine Schemes

The Ukraine Family Scheme allows applicants to join family members or extend their stay in the UK. The Ukraine Sponsorship Scheme allows Ukrainian nationals and their family members to come to the UK if they have a named sponsor under the Homes for Ukraine Scheme. The Ukraine Extension Scheme allows Ukrainian nationals and their immediate family members to apply for permission to stay in the UK. The reason for migration will predominantly only show the out-of-country routes, as opposed to the extension routes.

Future publication dates for international migration statistics are pre-announced on the ONS Release Calendar.

Our data policies detail how data are collected, secured and used in the publication of statistics. We treat the data that we hold with respect, keeping it secure and confidential, and we use statistical methods that are professional, ethical and transparent.

Feedback and enquiries

Your feedback is important. We want to hear what our users need from the development of these statistics to ensure we are providing the best insights on migration.

Please email pop.info@ons.gov.uk for any enquiries or to provide feedback.