• Where can I find annual data or data by single-year age groups?
  Annually interpolated time series for selected demographic indicators and population by single-year age groups are available for download in Excel or CSV file format from the Download Center. Note that special interpolation routines were used to produce estimates and projections for single calendar years (e.g., 1950, 1951, etc.) and for single-year age groups (e.g., 0, 1,2, 3, 4, 5, 6, 7, etc.). It must be noted, however, that interpolation procedures cannot recover the true series of events or the true composition of an aggregated age group. For further details about the interpolation procedures used, see report World Population Prospects 2019: Methodology of the United Nations Population Estimates and Projections.
• Why some data are only available for 5-year periods or 5-year age groups?
  The cohort-component method used in the 2019 Revision requires a uniform age format for the estimation of the size and structure of a population and the measurement of vital events. For the purpose of global population estimates and projections, most empirical data are only available in five-year age groups. As a consequence, all results produced by the cohort-component method in the 2019 Revision are also in five-year age groups and, for vital events, represent five-year periods. All vital rates are given as the average over the five-year period from mid-year (t) to mid-year (t+5) (the next 5-year projection period) centred on 1 January year (t+3). For example, the estimate for life expectancy at birth for 2015-2020 refers to the period from mid-2015 to mid-2020 (i.e., 2015.5 to 2020.5 in decimal dates), with 1 January 2018 as the mid-point (i.e., 2018.0 using a decimal date).
  Note that annually interpolated time series for selected demographic indicators and population by single-year age groups are available for download in Excel or CSV file format from the Download Center.
• What is the most recent Revision of World Population Prospects?
  The 2019 revision is the most recent revision of World Population Prospects, the official United Nations population estimates and projections. It was released on 17 June 2019.
• When will the next Revision of the World Population Prospects be released?
  The Population Division of the Department of Economic and Social Affairs of the United Nations issues a new Revision every two years. The next one is due on 11 July 2022 (World Population Day).
• What is the estimation period for the 2019 revision of the World Population Prospects?
  The 2019 revision provides population estimates for the period 1950-2020. Estimates of stocks are presented for every year that is a multiple of five from 1950 to 2020. Estimates of the components of population change are presented for five-year periods, starting with 1950-1955 and ending with 2015-2020. Stock estimates refer to 1 July of the year in question. Period estimates may be assumed to refer to the mid-point of the period concerned (e.g. the mid-point of the period 1 July 1970 to 1 July 1975 is the 1 January 1973). Data presented by single calendar years or single groups of age are derived by interpolation.
• What is the projection period for the 2019 revision of the World Population Prospects?
  The 2019 revision provides population projections for the period 2020-2100. There is only one series for the population estimates, but there are several series for the population projections, because different projection variants are calculated. Calculations are carried out by five-year periods using data classified by five-year age group. Projections of stocks are presented for every year that is a multiple of five from 2020 to 2100. Projections of the components of population change are presented for five-year periods, starting with 2020-2025 and ending with 2095-2100. Stock estimates refer to 1 July of the year in question. Data presented by single calendar years or single groups of age are derived by interpolation.
• Why are successive Revisions of World Population Prospects issued every two years?
  Governments have instructed the Population Division to follow a biennial cycle for the preparation of population estimates and projections. All Revisions of World Population Prospects provide a historical time series of population indicators starting in 1950. The 2019 revision provides projections up to 2100. Every new Revision takes into account newly released national data to revise estimates of past trends in fertility, mortality or international migration and to update population age distributions on the basis of newly available census data. See Methodology of the United Nations Population Estimates and Projections. For more information on the data used in preparing the 2019 revision, please refer to Data Sources
• What country aggregates are available?
  The 2019 revision of World Population Prospects presents aggregated data and indicators for sustainable development regions, development groups, income groups, major areas and geographical regions. These are part of the standard tabulations. In addition, data for several other country groups are available online in Excel format in the Special Aggregates. The data are aggregated for multiple functional groupings such as economic and trading groups, political groups, and United Nations regional groups or entities.
• Where can I find population estimates for periods before 1950?
  For a series of world population estimates starting in year zero, please refer to Table 1: World Population From Year 0 to Stabilization in The World at Six Billion, United Nations, 1999, p. 5.
  For a review of world population estimates prior to 1950 prepared by the United Nations see: John C. Caldwell and Thomas Schindlmayr (2002). Historical Population Estimates: Unraveling the Consensus, Population and Development Review, Vol. 28, No. 2 (Jun., 2002), pp. 183-204.
  See Excel file for plots and data table with world population estimates from year 0 to 1950, and 2019 revision estimates for 1950-2020 and projections for 2020-2100.
• Where can I find previous revisions of the World Population Prospects?
  Currently, once a new revision is issued, only the most recent revision of the World Population Prospects is available online. With each successive revision of the World Population Prospects, the Population Division of the United Nations estimates historical demographic trends for the period from 1950 to the present and projects future population trends out to 2100. The estimates are based on all available sources of data on population size and levels of fertility, mortality and international migration for 235 distinct countries or areas comprising the total population of the world. Users interested to analyze changes over time should use the estimates and projections available for the most recent revision to insure consistency and comparability between and across countries, data availability, methods and underlying assumptions. The World Population Prospects 2019 is the twenty-sixth edition of the United Nations population estimates and projections, which have been prepared since 1951 by the Population Division of the Department of Economic and Social Affairs. Results from earlier revisions are currently available only in out-of-print publications, and digital copies (scanned PDF) of these reports will be posted in the future (no estimated date yet). For advanced users and researchers, access to selected results from the 1992-2017 revisions is available at the Download Center - Archive.
• Why does the Population Division produce estimates of past population trends instead of using official national data?
  World Population Prospects presents estimates for 235 countries and areas. About half of those countries or areas do not report official demographic statistics with the detail necessary for the preparation of cohort-component population projections. The Population Division undertakes its estimation work in order to close those gaps. The availability of data gathered by major survey programs, such as the Demographic and Health Surveys or the Multiple-Indicator Cluster Surveys, are useful in generating some of the data that is not currently being produced by official statistics. See Methodology of the United Nations Population Estimates and Projections for further details.
• Why do the estimates in World Population Prospects sometimes differ from official statistics?
  Official statistics are not very perfect. All data have deficiencies. Official demographic statistics are affected by incompleteness of coverage, lack of timeliness and errors in the reporting or coding of the basic information. The analysis carried out by the Population Division takes into account those deficiencies and seeks to establish past population trends by resolving the inconsistencies affecting the basic data. Use of the cohort-component method to reconstruct populations is the major tool to ensure that the population trends estimated by the Population Division are internally consistent. See Methodology of the United Nations Population Estimates and Projections for further details.
  National Statistical Offices are well aware of the inconsistencies among data generated by different sources. Even in countries with advanced statistical systems, it is common for official statistical series to be revised retrospectively as new data become available and inconsistencies are corrected.
• Who is using the results of World Population Prospects?
  The users of World Population Prospects are many and varied. All entities of the United Nations system use the Population Division's population estimates for the calculation of indicators that require population as an input. The Division's population projections are also used in projecting other population-related variables or in modelling complex systems that use population is an exogenous variable. In addition, several entities and organizations of the United Nations distribute the results of World Population Prospects through their own databases and websites (e.g., the World Bank, UNESCO, UNICEF, World Health Organization, UNFPA, Statistics Division/DESA, United Nations Development Programme, International Labour Organization, Food and Agriculture Organization). In addition, the data are used by many groups belonging to civil society, from school-children learning about population to journalists to academics. Being the official United Nations population estimates and projections, the results of World Population Prospects are considered to embody the authoritative view of population levels, trends and characteristics.
• Which data sources are used for estimating fertility?
  The fertility estimates for the World Population Prospects are based on the following sources:

  Vital Registers

  Most developed and some developing countries have vital registration systems, which record the number of births and the age of the mother. This information can be combined with estimates of the female population by age to calculate age-specific fertility rates and total fertility. Countries either report the (age-specific) rates or the number of births by age of mother.

  Censuses

  The third major source of fertility information are the censuses, which typically provide information on the number of children ever born, or on the number of children born during the past 12 or 24 months for each woman age 15 to 49 enumerated. Census data, which provide full records for everyone living in a particular household, also allow application of various indirect measures to estimate fertility, such as the "reverse survival method" and the "own children method", which is based on the children of the women living in the household.

  Surveys

  Most developing countries do not have vital registration systems, or they have only vital registration in urban areas. In those countries, surveys are typically used to estimate fertility. The surveys are carried out by various institutions, from National Statistical Offices to international organizations. The most widely used surveys are the Demographic and Health Surveys (DHS) and the Multi-Indicator Cluster Surveys (MICS). In some countries, there are also Demographic Surveillance Sites (DSS), which provide in-depth fertility and health information for particular areas within these countries. Data from surveys are typically available in the form of birth histories (either full histories or histories truncated for the last 5 years) or as the number of "children ever born". Several data quality issues affect the collection of retrospective birth histories and the fertility levels and trends estimated based on these surveys need to be assessed critically. For further details about these issues, see Pullum, T. W., and S. Becker (2014), Evidence of Omission and Displacement in DHS Birth Histories, DHS Methodological Reports No. 11. Rockville, Maryland, USA: ICF International; and Schoumaker, B. (2014), Quality and Consistency of DHS Fertility Estimates, 1990 to 2012, DHS Methodological Reports No. 12. Rockville, Maryland, USA: ICF International. Sample surveys collect the same fertility information as the census and allow the application of the same types of estimation methods.

  Adjustments

  Fertility information from all data sources, including censuses, may require adjustments - particularly for historical time series. There are also various demographic techniques to adjust underreporting in particular age-groups.

  Additional information

  See Methodology of the United Nations Population Estimates and Projections. For more information on the data used in preparing the 2019 revision, please refer to Data Sources. For further details about the various analytical methods, see United Nations manuals on demographic indirect estimation methods, and Moultrie TA, RE Dorrington, AG Hill, K Hill, IM Timæus and B Zaba (eds). Tools for Demographic Estimation. UNFPA and International Union for the Scientific Study of Population (IUSSP).

Disclaimer: This web site contains data tables, figures, maps, analyses and technical notes from the current revision of the World Population Prospects. These documents do not imply the expression of any opinion whatsoever on the part of the Secretariat of the United Nations concerning the legal status of any country, territory, city or area or of its authorities, or concerning the delimitation of its frontiers or boundaries.