This page contains a summary of important quality information that you need to know before using this data.

The Subnational Population Projections Quality and Methodology Information PDF attached below contains further information on:

  • the strengths and limitations of the data

  • the quality of the output: including the accuracy of the data, how it compares with related data

  • uses and users

  • how the output was created

Important points about subnational population projections

  • Subnational population projections are estimates of the future resident population based on the continuation of recent demographic trends.

  • Projections relate to the usually resident population and do not include people who come to or leave the country for less than 12 months.

  • Since projections are produced in a consistent way, they can be used as a common framework for informing local level policy and planning. Local authorities are advised to supplement them with any local information they have.

  • As projections are carried forward, they become less accurate, particularly for smaller geographical areas and detailed age and sex breakdowns.

  • Projections are not able to accurately reflect exactly what future population levels are going to be. This is because they do not take account of local development, policies on growth, the capacity of an area or other economic and international factors.


Subnational population projections provide estimates of the future resident population and give an indication of the possible size and structure of the future population that might result if recent demographic trends were to continue. They are produced every two years and project the population for each year of a 25-year period from the base year.

They are produced using the cohort component methodology and are based on the local authority mid-year population estimates. Assumptions made about future fertility, mortality and migration at local authority level are based upon recent observed trends from the components of change which are published with the latest mid-year population estimates. The assumptions use either 5 or 6 years of trend data depending on the component. They are constrained to the equivalent national population projections for England.

Subnational population projections are produced in a consistent way across all areas and use a robust methodology so that they are relevant for all types of users. They are used in a number of ways, including: for local planning of health, education and other service provisions, as a basis for household projections, as a basis for projections produced by other organisations and for allocating funding to local authorities as part of the local government settlement calculations.

Each new set of subnational population projections supersedes the previous set. Comparisons can be made with earlier sets to show how the projections have changed over time and also to assess their accuracy by comparing projections with the final population estimates for a given year. However, these comparisons are not straightforward. More information can be found in the Quality and Methodology Information report in the section on comparability over time.

Projections produced by other organisations may not be comparable with these projections since they will use different methodologies and in some cases, additional local data. More information on the methodology used for the subnational population projections can be found in the Quality and Methodology Information report in the section on how the output is created.

We quality assure the administrative data used for these statistics to ensure that they are suitable for this purpose. To gain further insight on data quality issues and the impact on statistics, please see Quality Assurance of Administrative Data:

Download this methodology

Contact details for this Quality and methodology information

Andrew Nash
Telephone: 01329 444652