Another factor that causes groups to change in size is religious \u201cswitching\u201d<\/strong><\/a> \u2013 people moving into and out of religious groups, including people who choose to switch out of religion altogether.[12. numoffset=”12″ Children tend to be raised in the religion (or non-religion) of a parent. We use survey data to measure switching between childhood religion (or non-religion) and a respondent\u2019s current adult religion. However, religious change can also occur as the result of parents choosing not to raise children in their religion (or non-religion). In such a situation, religious change happens not due to switching<\/em> but because religious identity is not transmitted <\/em>between generations. There is little cross-national data measuring the frequency with which parents transmit their religious identity to children. This is an area for further research.]<\/p>\n\n\n\n The changes in religious composition that happened between 2010 and 2020 resulted from a combination of these factors. The importance of each factor varies by religion:<\/p>\n\n\n\n In addition to the demographic dynamics that affect religious change globall<\/em>y, migration<\/strong><\/a> is a large source of religious change within a few regions and countries. (Migration does not affect the size of religious groups at the global level.)<\/p>\n\n\n\n All else being equal, a younger population has a demographic \u201cadvantage\u201d for growth. That\u2019s because a young population has a relatively large percentage of women who are in \u2013 or soon will enter \u2013 their childbearing years, and a relatively small percentage of older adults nearing the end of their lives.<\/p>\n\n\n\n The effect of a group\u2019s age structure may be amplified or muted by its fertility rate. To understand religious change since 2010, it helps to look at where each of these indicators stood at the start of the decade.<\/p>\n\n\n\n In 2010, Muslims had a relatively advantageous age structure, while Jews, Buddhists and the religiously unaffiliated were at a demographic disadvantage. (Hindus are relatively young, but they are concentrated in countries with relatively low life expectancy.)<\/p>\n\n\n\n In most religious groups, about half of all women are in the broad reproductive age range of 15 to 49. But there is substantial variation in the share of women in the younger <\/em>reproductive age range of 15 to 29.[13. Fecundity (the ability to have children) is greater<\/a> for women under 30 than for women older than 30. Around the world, women under 30 typically have higher age-specific fertility rates<\/a> than older women. On average, women who start having children earlier in their lives have the potential to have more children than women who start bearing children at a later age. Nevertheless, in advanced economies it is common for women to delay childbearing. Among the Organization for Economic Co-operation and Development (OECD) countries, 30 to 34<\/a> is the age category during which women have children at the highest rate.]<\/p>\n\n\n\n In 2010, Muslims had a relatively large share of women in these younger reproductive years, followed by Hindus. On the other hand, Buddhists and Jews had smaller shares of women between the ages of 15 and 29.<\/p>\n\n\n\n When religion is transmitted from mother to child, and child mortality rates are low, groups with higher fertility rates will generally grow faster. (In this report, we focus on the total fertility rate, i.e., the average number of children a woman is expected to have in her lifetime.)[14. For more details on the total fertility rate and other measures of fertility, read Pew Research Center\u2019s publication \u201cIs U.S. fertility at an all-time low? Two of three measures point to yes<\/a>.\u201d]<\/p>\n\n\n\n Muslims were estimated to have the highest total fertility rate, with an average of 3.1 children per woman in the 2010-15 period, according to a previous Pew Research Center study<\/a>. Christians followed with 2.7 children.<\/p>\n\n\n\n Buddhists (1.6 children per woman), religiously unaffiliated people (1.7) and members of other religions (1.8) had the lowest fertility rates.<\/p>\n\n\n\n In the absence of change from migration, a group typically must have a total fertility rate of at least<\/em> 2.1 (\u201creplacement level\u201d) to maintain its size. However, it can take considerable time for below-replacement-level fertility rates to lead to population decline. For example, fertility rates in China dropped below the replacement level in the early 1990s<\/a>, but China\u2019s population did not begin to shrink until three decades later<\/a>.<\/p>\n\n\n\n If demographic factors were the only drivers of change, young groups with high fertility would usually grow more quickly than groups that are older and have fewer children. As of 2010, Christians around the world were younger and had more children, on average, than religiously unaffiliated people.<\/p>\n\n\n\n But demographic factors can be amplified or offset by another mechanism: religious \u201cswitching\u201d (i.e., people leaving one religion and joining another, or leaving religion altogether). Religious switching explains why Christian populations shrank between 2010 and 2020, while religiously unaffiliated populations grew. Christians have a high fertility rate, but they have been losing adherents as people switch out of Christianity<\/a> to become religiously unaffiliated.<\/p>\n\n\n\n Throughout this report, religious switching refers to a change between the religious group in which a person says they were raised (during their childhood) and their religious identity now (in adulthood).<\/p>\n\n\n\n We use the term \u201cswitching\u201d rather than \u201cconversion\u201d because many people who switch identities leave religion to become religiously unaffiliated.<\/p>\n\n\n\n We count changes between seven large religious categories (such as from Buddhist to Christian, or from Hindu to religiously unaffiliated) but not switching within the same category (such as from Protestant to Catholic).<\/p>\n<\/details>\n\n\n\n Pew Research Center previously has analyzed religious switching rates at the country level, within 102 countries and territories<\/a>. In the current report, we conducted a new analysis to understand how switching within countries impacted the size of religious groups on a global level<\/em>.[15. Outside China, data comes from Center surveys conducted between 2009 and 2024 in 96 places, and from International Social Survey Programme (ISSP) surveys conducted between 2008 and 2018 in 20 countries. Rates of religious switching are calculated using responses to two questions that have been consistently included in Pew Research Center surveys (\u201cWhat is your religion, if any?\u201d and \u201cThinking about when you were a child, in what religion were you raised?\u201d) and in International Social Survey Programme (ISSP) surveys (\u201cWhat is your religion, if any?\u201d and \u201cWhat religion, if any, were you raised in?\u201d). For China, we rely on the 2018 Chinese General Social Survey; specifically, the most recent wave that asked about respondents\u2019 religious upbringing. This survey asked about respondents\u2019 parent(s)\u2019 religion when the respondents were 14, and we use the mother\u2019s<\/em> religion as a proxy for their childhood religion. Read the Methodology<\/a> for more details.]<\/p>\n\n\n\n For this analysis, we aggregated rates of religious switching from 117 countries and territories that cover 92% of the 2010 global population.[16. Estimates are weighted to reflect the size of each group in any given country. For example, estimates for Hindus are weighted to account for the fact that India\u2019s Hindu population is much larger than the United States\u2019 Hindu population.] For the remaining 8%, or 84 countries and territories (with population sizes above 100,000 in either 2010 or 2020), we assume that no switching took place because we have no data measuring religious switching in this slice of the world.<\/p>\n\n\n\n Research on religious switching generally finds that if people move away from their childhood religion, they tend to do so by the end of their young adult years. For example, in the American Enterprise Institute\u2019s American National Family Life Survey<\/a>, 75% of respondents ages 65 and older who had left their childhood religion reported that they had done so by the time they were 30.<\/p>\n\n\n\n To capture recent religious switching and exclude more of the switching that happened during the last century, this analysis focuses on the experiences of survey respondents ages 18 to 54.<\/p>\n\n\n\n The surveys we analyze do not allow us to isolate the religious switching that took place exclusively between 2010 and 2020. Rather, they provide an overview of switching patterns that have shifted religious landscapes in recent decades.<\/p>\n\n\n\n (Read the Methodology<\/a> for more on our data and methods used to compute rates of religious switching.)[17. The rates of religious switching in this chapter describe the movement into and out of a given religious category in relation to the population raised in the group<\/em>. However, other Center reports, such as \u201cAround the World, Many People Are Leaving Their Childhood Religions<\/a>,\u201d reported switching rates among all adults <\/em>in each country.]<\/p>\n\n\n\n This analysis focuses on quantifying how common switching in and out is for each religious category. We find that, globally:<\/p>\n\n\n\n The religiously unaffiliated<\/strong> population has experienced the most growth from religious switching. On average, for every 100 people ages 18 to 54 who were raised with no religion, 7.5 people have left<\/em> and 24.2 have joined<\/em> the ranks of the unaffiliated, resulting in a net gain of 16.7 people.<\/p>\n\n\n\n Christians<\/strong> and Buddhists<\/strong> have experienced the greatest overall losses due to religious switching. For every 100 adults in the 18- to 54-year-old age range who were raised Christian, there was a net loss of 11.6 people (17.1 left and 5.5 joined). Buddhists have lost 9.8 people for every 100 raised Buddhist (22.1 left and 12.3 joined).<\/p>\n\n\n\n Muslims<\/strong> and Hindus<\/strong> have been the least likely to gain or lose adherents from religious switching. About one in every 100 adults raised Muslim (or Hindu) has left their childhood religion, and a similar number from a different religious category have switched into Islam (or Hinduism).[18. In India and Bangladesh, rates of switching into and out of Hinduism are low and they roughly balance out. In some other countries, there is a net movement out of Hinduism. For example, in Nepal, of 100 people raised Hindu, 4.3 leave and 0.3 join, a net change of 4.0 people. There is also modest net movement out of Hinduism in Sri Lanka<\/a>.]<\/p>\n\n\n\n Since Jewish populations are relatively small in most countries, survey data measuring Jewish switching patterns typically comes from a small number of respondents. However, we do have sufficient data to measure movement into and out of Judaism in Israel and the U.S. In our 2024 Israel survey<\/a>, rates both of entering and of leaving Judaism were very low. In the U.S. Religious Landscape Studies we conducted in 2014<\/a> and in 2023-24<\/a>, leaving Judaism was slightly more common than joining the religion, though the difference was within the margins of error.<\/p>\n\n\n\n An additional complication is that many people who cease to identify religiously<\/em> as Jewish may continue to identify as Jewish in some other way<\/a>, such as culturally, ethnically, or by family background. In our analyses of religious switching, we use the term \u201cJewish\u201d to refer only to religious identity, because the survey questions ask about a person\u2019s current religion and what religious group they were raised in (their childhood religion).<\/p>\n\n\n\n The \u201cother religions\u201d category also makes up a small share of respondents in most countries. Due to concerns about the small sample sizes for Jews and members of other religions in many surveys, global rates of switching for these groups are not shown in this report. For more details, read the Methodology<\/a>.<\/p>\n\n\n\n There can be more growth in a population if death rates decline and people gradually live longer lives. We can describe mortality patterns with statistics about the number of deaths experienced for every 1,000 people in various age groups over a given period. However, it is often simpler to consider what these death rates suggest about the expected longevity<\/em> of human life. <\/p>\n\n\n\n Life expectancy at birth \u2013 an approximate estimate of the expected lifespan of an average newborn child \u2013 is a convenient snapshot of the mortality rates at a moment in time.[19. This is a \u201cperiod life expectancy<\/a>\u201d measure based on mortality rates observed at one point in time.] If all other factors were equal, groups with higher life expectancies in 2010 would live longer and have larger populations by 2020.<\/p>\n\n\n\n Among all religious groups, Jews were concentrated in countries with the highest life expectancy at birth in 2010, with an estimated global average of 80 years, followed by the religiously unaffiliated (76) and Buddhists (74). Hindus and Muslims were concentrated in countries with the lowest life expectancy, 67 years for each, well below the global average of 70 years.<\/p>\n\n\n\n Because no global data is available on how life expectancy varies by religion within countries, we estimate global life expectancy for each religious group by assuming that people in all religious groups have the average life expectancy of the country in which they live.<\/p>\n\n\n\n Therefore, global differences between religious groups reflect their differences in geographic concentration patterns. For instance, the high life expectancy among Jews reflects the fact that the vast majority of the world\u2019s Jews live in either the United States or Israel, where life expectancy for 2010 was well above the global average, at 79 and 82 years, respectively.<\/p>\n\n\n\n For more information about life expectancy and religion, refer to Chapter 1 of our 2015 study \u201cThe Future of World Religions: Population Growth Projections, 2010-2050<\/a>.\u201d<\/p>\n<\/details>\n\n\n\n Migration cannot change the size of global <\/em>religious populations, but it is a primary driver of change in the size of some religious groups in certain parts of the world. Migration contributes especially to the growth of non-Muslims in the Gulf Cooperation Council (GCC) countries and the growth of Muslims in North America and Europe.<\/p>\n\n\n\n Between 2010 and 2020, the number of people living outside their country of birth rose by more than 50 million (about the size of Italy\u2019s total population), according to the United Nations\u2019 migrant stock estimates<\/a>. In addition to the ongoing movement of people to wealthy nations in search of economic opportunities, much of the surge in migrants during this period can be attributed to Syrians fleeing civil war<\/a> (about 7.5 million) and Venezuelans fleeing economic and political instability<\/a> (roughly 5 million).<\/p>\n\n\n\n Generally, migration has a limited impact on a country\u2019s religious makeup because migrants often constitute a small fraction of a society\u2019s total population, and migrants often move to countries where their religious identity is already prevalent. For instance, the vast majority of Syrian refugees arriving in Turkey over the past decade are Muslims, and Venezuelans moving to the nearby countries of Colombia, Peru and Ecuador are predominantly Christians. In these places, the surge of migrants itself was not the cause of much religious change between 2010 and 2020.<\/p>\n\n\n\n Still, migration did affect the religious mix in some places between 2010 and 2020. For example, in Lebanon, which was 62% Muslim in 2010, the large influx of Syrian refugees contributed to a 5 percentage point increase in the share of Lebanon\u2019s population that was Muslim in 2020.<\/p>\n\n\n\n Among the GCC countries, Oman experienced a large increase in the share of its population that is not<\/em> Muslim. Non-Muslims \u2013 mostly Christians and Hindus \u2013 now comprise 19% of Oman\u2019s population (up 8 points), as of 2020. In Kuwait, the United Arab Emirates and Saudi Arabia, the share of non-Muslims rose by 2 points each.<\/p>\n\n\n\n The six GCC countries (Bahrain, Kuwait, Oman, Qatar, Saudi Arabia and the United Arab Emirates) have some of the world\u2019s largest shares of foreign-born residents. And unlike native-born GCC residents (who almost always identify as Muslim), about a quarter of migrants living in GCC countries (who mostly originate from South Asia) are estimated to be Christians and Hindus, according to Pew Research Center\u2019s 2024 study of the religious composition of the world\u2019s migrants<\/a>.<\/p>\n\n\n\n Europe\u2019s Muslim population growth since 2010 also has been driven largely by migration. In 2020, Muslims made up 6% of Europe\u2019s population, up about 1 point from 2010. Growth was concentrated in Sweden, Austria and Germany, which took in large numbers of Syrian war refugees<\/a>. The region\u2019s total Muslim count increased by 6.2 million during the decade, including an estimated 3.5 million Muslims who were born outside Europe. Nearly 1 million came from Syria.<\/p>\n\n\n\n Migration accounted for a large portion of the increase in North America\u2019s Muslim population, which grew to make up 1.6% of the region\u2019s residents in 2020 (up 0.4 points). Muslim migrants to North America came primarily from South Asia and the Middle East-North Africa region. Migration also fueled the growth of Hindus in North America, whose share increased to 1.0% (up 0.3 points).<\/p>\n\n\n\n\n
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Age structure and fertility<\/h3>\n\n\n\n
Age structure<\/h4>\n\n\n\n
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<\/a><\/figure>\n\n\n\nFertility<\/h4>\n\n\n\n
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<\/a><\/figure>\n\n\n\nReligious \u2018switching\u2019<\/h3>\n\n\n\n
What is religious \u2018switching\u2019?<\/summary>\n
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<\/a><\/figure>\n\n\n\nMortality (life expectancy)<\/h3>\n\n\n\n
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<\/a><\/figure>\n\n\n\nHow we approximate life expectancy by religion<\/summary>\n
Migration<\/h3>\n\n\n\n