FOI reference: FOI-2025-2914
You asked
Please provide the following:
1. The most recent set of assumptions used by the ONS in its household projections for England, including:
- Net migration assumptions
- Household formation rates by age and gender
- Average household size trends
- Population growth assumptions
2. Specific clarification on whether these household projections have been used by the government (e.g., DLUHC or HM Treasury) to support public housing targets, including the stated aim to build 1.5 million homes by 2029.
3. Any correspondence or documentation shared between the ONS and other departments in relation to housing need or household projection assumptions since January 2022.
We said
Thank you for your request.
1. In answer to your first questions.
Net migration assumptions:
The most recent household projections (2018-based) will have taken assumptions for net migration from the 2018-based National Population Projections, which would have looked at international migration that occurred in the 25-year period from mid-1994 to mid-2018. The methodology is available on the ONS website National population projections, how the assumptions are set: 2018-based.
Household formation rates by age and sex:
Patterns of household formation were derived from 2001 and 2011 census data. Rates were calculated based on these patterns. These rates were applied to population and household numbers to show the potential number of households there would be in England in the future if assumptions about the size and structure of the population, and that population's patterns of household formation, were realised in practice.
Average household size trends:
Our latest household projections were calculated by dividing the total projected household population of a local authority by the number of projected households. The population data were derived from mid-year estimates (MYE) or subnational population projections (SNPP) and the household data derived from the 2001 and 2011 censuses.
Population growth assumptions:
Assumptions in population growth were derived from the 2018-based Subnational population projections, which in turn were themselves derived from the 2018-based National Population Projections. Assumptions were set using the most recent births, deaths and migration trends at the time with input from experts in fertility, mortality and migration.
2. For any decision-making by government please request this from the relevant department(s). We do not have a record of all uses and potential uses in public housing targets.
3. Relevant extracts of correspondence and documentation shared between the ONS and other departments in relation to housing need or household projection assumptions since January 2022 can be found in the associated download. We have interpreted housing need and household projection assumptions to refer to a specific term relating to the Ministry for Housing Communities and Local Government's calculations of housing and economic needs assessment, which essentially sets local authority housing targets.
Personal data has been redacted under s.40(2) of the Freedom of Information Act 2000 (FOIA). Some sections of the documents have also been redacted as they focus on an unrelated topic, so are out of scope of the request. Some sections have also been redacted as they are outside the scope of this request.