Claims to be the fastest-growing religion
Many different religions currently or previously have claimed to be the fastest growing religion. The world's largest religions that are showing increases that outrun birth-rate include Islam, Christianity,and Hinduism. There is often little coverage of the "unaffiliated" category (which includes agnostics, atheists, deists, and theists), although some evidence suggests this group is growing rapidly (see "Nonreligious" below). "The" fastest growing religion depends on the definition (below), such as absolute number vs. percentage, conversions only or also births, etc., how broadly a religion is defined (e.g., Christianity as a whole, or a particular denomination), and the period and region in question.
Religions can grow in numbers because of conversion or because of higher birth rates in a religious group or both. Measures counting absolute numbers tend to favour the larger religions ( Islam, Christianity, Hinduism for example which have at least 1 billion followers and more). Measures counting percentage growth tend to favour smaller ones such as Wicca, Falun Gong and other minority religions.
The fastest growing religion could refer to:
- The religion whose absolute number of adherents is growing the fastest.
- The religion that is growing fastest in terms of percentage growth per year.
- The religion that is gaining the greatest number of converts in the world.
Data collection 
Statistics on religious adherence are difficult to gather and often contradictory; statistics for the change of religious adherence are even more so, requiring multiple surveys separated by many years using the same data gathering rules. This has only been achieved in rare cases, and then only for a particular country, such as the American Religious Identification Survey in the USA, or census data from Australia (which has included a voluntary religious question since 1911).
Buddhism is being recognized as the fastest growing religion in Western societies both in terms of new converts and more so in terms of friends of Buddhism, who seek to study and practice various aspects of Buddhism. As in the United States, Buddhism is ranked among the fastest growing religions in many Western European countries.
The Australian Bureau of Statistics through statistical analysis held Buddhism to be the fastest growing spiritual tradition/religion in Australia in terms of percentage gain with a growth of 79.1% for the period 1996 to 2001 (200,000→358,000).
Buddhism is the fastest-growing religion in England's jails, with the number of followers rising eightfold over the past decade.
According to a 2005 paper submitted to a meeting of the American Political Science Association, most of this growth has occurred in non-Western countries and concludes the Pentecostalism movement is the fastest growing religion worldwide.
In Vietnam, the US Department of State estimates that Protestants in Vietnam may have grown 600% over the last decade. In Nigeria, the numbers of Christians has grown from 21.4% in 1953 to 48.2% in 2003. In South Africa, Pentecostalism has grown from 0.2% in 1951 to 7.6% in 2001. In South Korea, Christianity has grown from 20.7% in 1985 to 29.2% in 2005 according to the Pew Forum. However, Protestant Christianity is now seeing a decline in the country due to scandals involving church leadership and an increasing negative outlook at Protestant missionary tactics. As a result, Catholicism and Buddhism have become the fastest growing religions in South Korea. In China, a recent boom in the Christian population has been called one of the "greatest revivals in Christian history"- Christians now comprise 5% of China, despite considerable persecution under Chairman Mao. In fact, the Christian population is expected to reach over 400 million people by 2040, which will make China the largest Christian country on Earth.
Evangelical Christian denominations are among the fastest growing denominations in some Catholic Christian countries, such as Brazil and France.[unreliable source?] In Brazil, the total number of Protestants jumped from 16.2% in 2000 to 22.2% in 2010 (For the first time the percentage of Catholics in Brazil is less than 70%).
The records of The Church of Jesus Christ of Latter-day Saints show membership growth every decade since its beginning in the 1830s. Following initial growth rates that averaged 10% to 25% per year in the 1830s through 1850s, it grew at about 4% per year through the last four decades of the 19th century. After a steady slowing of growth in the first four decades of the 20th century to a rate of about 2% per year in the 1930s (the Great Depression years), growth boomed to an average of 6% per year for the decade around 1960, staying around 4% to 5% through 1990. After 1990, average annual growth again slowed steadily to a rate around 2.5% for the first decade of the 21st century, still double the world population growth rate of 1.2% for the same period. Rodney Stark predicts that it could become a major world religion by the end of the 21st century if the current growth trend of between 30% and 50% per decade continues. Currently its growth rate, not internationally but in the United States, is at 1.6%, about the rate of the growth of the rest of the U.S. population., which is still the largest growth of the top ten largest Christian denominations, with many other churches having negative growth.
The 2001 American Religious Identification Survey (ARIS) survey, which involved 50,000 participants, reported that the number of participants in the survey identifying themselves as deists grew at the rate of 717% between 1990 and 2001. If this were generalized to the US population as a whole, it would make deism the fastest-growing religious classification in the US for that period, with the reported total of 49,000 self-identified adherents representing about 0.02% of the US population at the time.
80% of the population of the Republic of India are Hindus, accounting for about 90% of Hindus worldwide. Their 10-year growth rate is estimated at 20% (based on the period 1991 to 2001), corresponding to a yearly growth close to 2% or a doubling time of about 38 years. However, the percentage of Hindus in the population of India has decreased by 3 percentage points since 1961, dropping from 83.5% in 1961 to 80.5% in 2001.
According to the Guinness Book of World Records, Islam is the world’s fastest-growing religion by number of conversions each year: "Although the religion began in Arabia, by 2002 80% of all believers in Islam lived outside the Arab world. In the period 1990-2000, approximately 12.5 million more people converted to Islam than to Christianity". Part of the book's quote can be seen online from this extract from Google Books. This was again shown in the 2005, 50th anniversary edition of Guinness Book of World Records, although the number of conversions was not mentioned this time.
In 1990, 935 million people were Muslims. According to the BBC, a comprehensive American study concluded in 2009 the number stood at approximately 23% of the world population with 60% of Muslims living in Asia. The report was done by the Pew Forum Research Centre. The forum also projected that in 2010 out of the total number of Muslims in the world 62.1% will live in Asia.
However the report also included a statement saying "While the global Muslim population is expected to grow at a faster rate than the non-Muslim population, the Muslim population nevertheless is expected to grow at a slower pace in the next two decades than it did in the previous two decades. From 1990 to 2010, the global Muslim population increased at an average annual rate of 2.2%, compared with the projected rate of 1.5% for the period from 2010 to 2030". The report also made reference to the fact that Muslims are estimated to make up 23.4% of the total global population in 2010 (out of a total of 6.9 billion people) and that by 2030 Muslims will represent about 26.4% of the global population (out of a total of 7.9 billion people). The Pew report also highlights that there is insufficient data available on religious conversion from its own findings given the complexities of identity and the difficulties of obtaining data: "Statistical data on conversion to and from Islam are scarce. What little information is available suggests that there is no substantial net gain or loss in the number of Muslims through conversion globally...
The American Religious Identification Survey gives Wicca an average annual growth of 143% for the period 1990 to 2001 (from 8,000 to 134,000 - U.S. data / similar for Canada & Australia). According to The Statesman Anne Elizabeth Wynn claims "The two most recent American Religious Identification Surveys declare Wicca, one form of paganism, as the fastest growing spiritual identification in America". The "Free Press Release Distribution Service" claims Wicca is one of the fastest growing religions in the United States as well. Wicca which is largely a Pagan religion is primarily attracting the followers of nature based religions in the Southern United States which is contributing towards its growth.
Variously defined, irreligion appears to be increasing (along with secularization generally). It is increasing in absolute numbers with overall population growth, but is decreasing as a percentage of the world population, due primarily to population increases in more religious developing countries outpacing population growth (or decline) in less religious developed countries. (See the geographic distribution of atheism.)
The American Religious Identification Survey gave nonreligious groups the largest gain in terms of absolute numbers: 14.3 million (8.4% of the population) to 29.4 million (14.1% of the population) for the period 1990–2001 in the U.S. Reuters describes how a study profiling the "no religion" demographic found that the so-called "nones", at least in the U.S., are the fastest growing religious affiliation category. This group consists of 33% agnostics, 33% theists, and 10% atheists. A 2012 study by the Pew Forum on Religion & Public Life reports, "The number of Americans who do not identify with any religion continues to grow at a rapid pace. One-fifth of the U.S. public – and a third of adults under 30 – are religiously unaffiliated today, the highest percentages ever in Pew Research Center polling."
A similar pattern has been found in other countries such as Australia, Canada, and Mexico. According to statistics in Canada, the number of "Nones" increased by about 60% between 1985 and 2004. In Australia, census data from the Australian Bureau of Statistics give "no religion" the largest gains in absolute numbers over the 15 years from 1991 to 2006, from 2,948,888 (18.2% of the population that answered the question) to 3,706,555 (21.0% of the population that answered the question). According to INEGI, in Mexico, the number of atheists grows annually by 5.2%, while the number of Catholics grows by 1.7%. In New Zealand, over 34% of the population are irreligious making it largest percentage of total population in Oceania region.
See also 
- "American Nones: The Profile of the No Religion Population". American Religious Identification Survey. 2008. Retrieved 19 October 2012.[dead link]
- "'No Religion' on the Rise: One-in-Five Adults Have No Religious Affiliation". Pew Forum on Religion & Public Life. 9 October 2012. Retrieved 19 October 2012.
- American Religious Identification Survey, Key Findings The Graduate Center of the City University of New York
- "2006 Census Tables : Australia".
- Buddhism fastest growing religion in West | Asian Tribune
- Western Buddhism: New insights into the West fastest growing religion: New Insights into the Wests Fastest Growing Religion: Amazon.co.uk: Kulananda: Books
- Buddhism in France is booming
- Year Book Australia, 2003 Australian Bureau of Statistics
- Beckford, Martin (2009-08-05). "Buddhism is fastest-growing religion in English jails over past decade". The Daily Telegraph (London).
- Barker, Isabelle V. (2005). "Engendering Charismatic Economies: Pentecostalism, Global Political Economy, and the Crisis of Social Reproduction". American Political Science Association. pp. 2, 8 and footnote 14 on page 8. Retrieved March 25, 2010.
- "Annual Report on International Religious Freedom for 2005 - Vietnam". U.S. Department of State. 2005-06-30. Retrieved 2007-03-11.[dead link]
- Religious Demographic Profiles - Pew Forum
- Pew Forum - Presidential Election in South Korea Highlights Influence of Christian Community
- China: the future of Christianity? | Antonio Weiss | Comment is free | guardian.co.uk
- Millions of Brazilians march for Jesus | Deseret News
- French Evangelicals through an American lens
- (Portuguese) Percent of Brazilian Catholics is below 70% for the first time
-  The Rise of Mormonism
- Phillips, Rick; Cragun, Ryan T., Mormons in the United States 1990-2008: Socio-demographic Trends and Regional Differences, Trinity College
- Brooks, Joanna (February 2, 2012), Mormon Numbers Not Adding Up, Religion Dispatches
- Yeakley, Richard (February 15, 2011). "Growth stalls, falls for largest U.S. churches". USA Today. (Religion News Service).
- "Census of India.". Census of India. Census Data 2001: India at a glance: Religious Composition. Office of the Registrar General and Census Commissioner, India. Retrieved 2008-11-26. The data is "unadjusted" (without excluding Assam and Jammu and Kashmir); 1981 census was not conducted in Assam and 1991 census was not conducted in Jammu and Kashmir.
- Guinness World Records 2003. Guinness World Records. 2003. p. 142.
- Guinness World Records 2005: Special 50th Anniversary Edition (50th ed.). Amazon.com.
- "The Future of the Global Muslim Population". Pew Forum Research Centre.
- "One in four is Muslim, study says". BBC News Website. 2009-10-08.
- American Religious Identification Survey, Full PDF Document The Graduate Center of the City University of New York
- (Elizabeth) Wynn, Anne. "Our year-long exploration of religions ends with Unitarianian Universalism and paganism". The Statesman.com. Retrieved 2 January 2012.
- "PRLog (Press Release) "Wicca"- The Fastest Growing Belief System In The World Today!". PRLog. Retrieved 2 January 2012.
- Puffer, Nancy. "Rise in paganism in Southeast Valley mirrors U.S. trend". azcentral.com. Retrieved 2 January 2012.
- Faith World, “No religion” segment of U.S. population profiled
- http://www.statcan.gc.ca/pub/11-008-x/2006001/9181-eng.htm#decline StatsCan, "Who is Religious?" by by Warren Clark and Grant Schellenberg
- 2006 Census Table : Australia
- México sigue siendo católico… pero crece el número de ateos
- Catholic News Agency