The population of the United Kingdom was estimated at 67,596,281 in 2022. It is the 21st most populated country in the world and has a population density of 279 people per square kilometre, with England having significantly greater density than Wales, Scotland, and Northern Ireland. Almost a third of the population lives in south east England, which is predominantly urban and suburban, with 8,866,180 people in the capital city, London, whose population density was 5,640 inhabitants per square kilometre (14,600/sq mi) in 2022.
Demography is the statistical study of human populations: their size, composition, and how they change through the interplay of fertility (births), mortality (deaths), and migration.
In demography, demographic transition is a phenomenon and theory which refers to the historical shift from high birth rates and high death rates to low birth rates and low death rates, as societies attain more technology, education and economic development. The demographic transition has occurred in most of the world over the past two centuries, bringing the unprecedented population growth of the post-Malthusian period, then reducing birth rates and population growth significantly in all regions of the world. The demographic transition strengthens economic growth process by three changes: (i) reduced dilution of capital and land stock, (ii) increased investment in human capital, and (iii) increased size of the labor force relative to the total population and changed age population distribution. Although this shift has occurred in many industrialized countries, the theory and model are frequently imprecise when applied to individual countries due to specific social, political and economic factors affecting particular populations.
A baby boom is a period marked by a significant increase of births. This demographic phenomenon is usually ascribed within certain geographical bounds of defined national and cultural populations. The cause of baby booms involves various fertility factors. The best-known baby boom occurred in the mid-twentieth century, sometimes considered to have started after the end of the Second World War, sometimes from the late 1940s, and ending in the 1960s. People born during this period are often called baby boomers.
Fertility in colloquial terms refers the ability to have offspring. In demographic contexts, fertility refers to the actual production of offspring, rather than the physical capability to reproduce, which is termed fecundity. The fertility rate is the average number of children born during an individual's lifetime. In medicine, fertility refers to the ability to have children, and infertility refers to difficulty in reproducing naturally. In general, infertility or subfertility in humans is defined as not being able to conceive a child after one year of unprotected sex. The antithesis of fertility is infertility, while the antithesis of fecundity is sterility.
Birth rate, also known as natality, is the total number of live human births per 1,000 population for a given period divided by the length of the period in years. The number of live births is normally taken from a universal registration system for births; population counts from a census, and estimation through specialized demographic techniques. The birth rate is used to calculate population growth. The estimated average population may be taken as the mid-year population.
Zero population growth, sometimes abbreviated ZPG, is a condition of demographic balance where the number of people in a specified population neither grows nor declines; that is, the number of births plus in-migrants equals the number of deaths plus out-migrants. ZPG has been a prominent political movement since the 1960s.
The dependency ratio is an age-population ratio of those typically not in the labor force and those typically in the labor force. It is used to measure the pressure on the productive population.
The total fertility rate (TFR) of a population is the average number of children that are born to a woman over her lifetime, if they were to experience the exact current age-specific fertility rates (ASFRs) through their lifetime, and they were to live from birth until the end of their reproductive life.
Sub-replacement fertility is a total fertility rate (TFR) that leads to each new generation being less populous than the older, previous one in a given area. The United Nations Population Division defines sub-replacement fertility as any rate below approximately 2.1 children born per woman of childbearing age, but the threshold can be as high as 3.4 in some developing countries because of higher mortality rates. Taken globally, the total fertility rate at replacement was 2.33 children per woman in 2003. This can be "translated" as 2 children per woman to replace the parents, plus a "third of a child" to make up for the higher probability of males born and mortality prior to the end of a person's fertile life. In 2020, the global average fertility rate was around 2.4 children born per woman.
Population decline, also known as depopulation, is a reduction in a human population size. Throughout history, Earth's total human population has continued to grow; however, current projections suggest that this long-term trend of steady population growth may be coming to an end.
Population growth is the increase in the number of people in a population or dispersed group. Actual global human population growth amounts to around 83 million annually, or 1.1% per year. The global population has grown from 1 billion in 1800 to 8.1 billion in 2024. The UN projected population to keep growing, and estimates have put the total population at 8.6 billion by mid-2030, 9.8 billion by mid-2050 and 11.2 billion by 2100. However, some academics outside the UN have increasingly developed human population models that account for additional downward pressures on population growth; in such a scenario population would peak before 2100. Others have challenged many recent population projections as having underestimated population growth.
A population pyramid or "age-sex pyramid" is a graphical illustration of the distribution of a population by age groups and sex; it typically takes the shape of a pyramid when the population is growing. Males are usually shown on the left and females on the right, and they may be measured in absolute numbers or as a percentage of the total population. The pyramid can be used to visualize the age of a particular population. It is also used in ecology to determine the overall age distribution of a population; an indication of the reproductive capabilities and likelihood of the continuation of a species. Number of people per unit area of land is called population density.
The ageing of Europe, also known as the greying of Europe, is a demographic phenomenon in Europe characterised by a decrease in fertility, a decrease in mortality rate, and a higher life expectancy among European populations. Low birth rates and higher life expectancy contribute to the transformation of Europe's population pyramid shape. The most significant change is the transition towards a much older population structure, resulting in a decrease in the proportion of the working age while the number of the retired population increases. The total number of the older population is projected to increase greatly within the coming decades, with rising proportions of the post-war baby-boom generations reaching retirement. This will cause a high burden on the working age population as they provide for the increasing number of the older population.
The relationship between fertility and intelligence has been investigated in many demographic studies. There is evidence that, on a population level, measures of intelligence such as educational attainment and literacy are negatively correlated with fertility rate in some contexts.
Population projections are attempts to show how the human population statistics might change in the future. These projections are an important input to forecasts of the population's impact on this planet and humanity's future well-being. Models of population growth take trends in human development and apply projections into the future. These models use trend-based-assumptions about how populations will respond to economic, social and technological forces to understand how they will affect fertility and mortality, and thus population growth.
Fertility factors are determinants of the number of children that an individual is likely to have. Fertility factors are mostly positive or negative correlations without certain causations.
In recent decades, the fertility rate of the United States has declined below replacement level, prompting projections of an aging population and workforce, as is already happening elsewhere in the developed world and some developing countries. The decline has been most noticeable since after the Great Recession of the late 2000s. Nevertheless, the rate of aging in the United States remains slower than that seen in many other countries, including some developing ones, giving the nation a significant competitive advantage. Unintentional pregnancies have become less common; in particular, teenage pregnancies have dropped to record lows.
The population of the United Kingdom is getting increasingly older, due to longer life expectancy and a sub-replacement fertility rate for little under 50 years. The society is expected to change as a result culturally and economically. By 2050, 1 in every 4 people is expected to be above the age of 65 and this will be more extreme in certain areas of the country.
Generation Alpha is a social cohort born between the early 2010s and mid 2020s. The birth years of Generation Alpha have seen a decline in birth rates, especially in the developed world.
