In 2020, around 98.5 percent of the Iranian population identified as Muslim. Around 81 percent identified as Shia Muslims in the same year, while a much smaller share followed the Sunni Muslim religion. In Iran, most Sunni Muslims belong to ethnic minority groups.

Iran’s demographics
The total population in Iran has grown steadily and is expected to surpass 90 million in 2028. The vast majority of the population in the country was between 15 and 64 years of age. At the same time, the share of people aged above 64 increased in recent years and constituted over seven percent of the total population.

Muslim population worldwide

In Europe, it was estimated that the Muslim population could triple by the middle of the century. In Southeast Asia, Indonesia had the largest share of Muslims as a proportion of its population. On the African continent, the highest number of Muslims was estimated in Nigeria, with close to a hundred million Islam followers. In the United States, less than one percent of the population identified as Muslims.

As of 2020, around 98.5 percent of the Iranian population identify as Muslims. According to forecasts for 2050, the share of Muslims in Iran was projected to slightly decline by 0.3 percent.

This statistic illustrates the distribution of Sunni and Shia amongst Muslim population in Iran and Saudi Arabia as of 2009. As of 2009, around 73 million Iranian Muslims belonged to the Shia faith, whereas only 4.8 million people in Saudi Arabia followed Shia Islam.

In 1800, the population of the modern-day territory of Iran was approximately 6.3 million. This figure would see modest growth throughout the 19th century, as several wars and a mass famine in 1870-1871 (modern estimates put its death toll at around 1.5 million people) were largely balanced out by a surge in migration to Iran; this migration came as the Russian Empire expanded into the Caucuses, and caused a wave of refugees to flee southwards to avoid forced expulsion and ethnic cleansing in the North Caucasus region, particularly from 1864 onwards. As a result, the population of Iran reached ten million by the turn of the 20th century.

Twentieth century growth Iran’s population would begin to grow rapidly in the 20th century, as the discovery of oil in the country in 1908 led to an economic boom, and the socio-economic reforms implemented under Reza Shah would see a number of medical and healthcare advancements across the country. Although unpopular with religious fundamentalists, Reza Shah's reforms had long-term influence on the demographic development of Iran, even after his abdication in 1941. Following the Second World War, Iran became increasingly westernized and developed relatively strong relations with the U.S.; however, western influence, economic imbalances and the oppression of the Mohammed Reza Shah's regime became the driving forces behind the Iranian Revolution, which was one of the most significant moments in the history of the region.

Growth after the Revolution The 1979 Iranian Revolution saw the removal of the Shah and an end to Iran's so called westernization; the monarchy was replaced by an Islamic, theocratic regime led by the Supreme Leader, Ayatollah Ruhollah Khomeini. During Khomeini's decade in charge he oversaw Iran's transition into an Islamic Republic, which implemented radical political and cultural changes in the country, and this coincided with an increased population growth rate in the 1980s. This growth was promoted by the Iranian government, who encouraged a baby boom during the Iran–Iraq War between 1980 and 1988, as part of an effort to increase future Iranian military manpower. As a result of this strategy, the population of Iran would grow from approximately 38.6 million in 1980 to over 56 million just a decade later. Following the implementation of a UN-brokered ceasefire in 1988, population growth in Iran would slow, as economic sanctions and government implementation of family planning policies would lead to a drop in fertility. Population growth has continued steadily into the 21st century, however, and in 2020, Iran is estimated to have a population of 84 million.

As of 2020, 32.2 percent of Iranian survey respondents stated that they follows the Shia Muslim belief. This was followed by 22.2 percent of respondents who said that they have no religious belief.

Iran, République islamique d’: Muslims as percent of the total population: Pour cet indicateur, The Cline Center for Democracy fournit des données pour la Iran, République islamique d’ de 1960 à 2013. La valeur moyenne pour Iran, République islamique d’ pendant cette période était de 98 pour cent avec un minimum de 98 pour cent en 1960 et un maximum de 99 pour cent en 2012.

In 1925, the total fertility rate of Iran was just over seven children per woman, meaning that the average woman in Iran could expect to have seven children over the course of their reproductive years. The fertility rate would see little change from this figure until the late 1960s, when modernization and significant decreases in child mortality would lead the fertility rate to fall to just over 6.2 in 1975. However, fertility would begin to rise again in the 1980s, as the modernization policies of the Shah would be replaced by Islamic economic and social platforms with the 1979 Islamic Revolution in the country. The total fertility rate in the country would peak at just over 6.5 children per woman in 1985, in response to strong encouragement by the Iranian government promoting larger families to improve Iran’s manpower advantage over Iraq in the 1980-1988 Iraq-Iran War. Following the war’s end with a UN-brokered ceasefire in 1988, fertility would fall sharply in the country, falling to 2.4 by the turn of the century, and falling below replacement-level in 2005. However, after bottoming out at 1.82 in 2010, fertility has risen somewhat in recent years, as the Iranian government has rolled out a series of economic incentives aimed at increasing fertility in the country. As a result, in 2020, the total fertility rate in Iran is estimated to have risen slightly, to 2.15 children per woman, above replacement-level.

The Bahá’í faith is one of the world's youngest major religions, having been founded in 19th century Persia (now Iran) by the prophet Bahá’u’lláh. Bahá’u’lláh had been a follower of a merchant called the Báb, who had developed a substantial following in Persia after claiming to be a manifestation of god. This small but growing religion was brutally suppressed by the Shia Muslim authorities in Persia, with the Báb himself being executed in 1850. Following this, Bahá’u’lláh fled into exile in Baghdad, in present-day Iraq, where he began to preach that he was the next in the line of God's messengers after the Báb. Both of the prophets claimed the lineage of all Abrahamic religions, combining beliefs from Islam, Christianity, and Judaism. Bahá’u’lláh was eventually forced to settle in the coastal city of ‘Akká, Palestine (now Acre, Israel) where he died in 1892. The site of his death became the central place of pilgrimage in the Bahá’í faith, and is why the center of the religion is today in the nearby city of Haifa. Beliefs of the Bahá’í The Bahá’í are perhaps unique for a major religion, as rather than emphasizing the correctness of their own beliefs over other religions, followers of Bahá’í believe that there is truth in all world religions and that there should be peace and harmony among the different faiths. Bahá’ís recognize the prophets and messengers of the different world religions as all part of the same process of revelation by God to humanity. While they believe in plurality among those who bring God's message, the Bahá’í are monotheistic and believe in only one god, rather than multiple. Bahá’u’lláh taught that the different religions developed to convey the same message of God, but in different societies and time periods, meaning that the message has been delivered in different ways to suit the needs of the time and place. The key teachings of the Bahá’í faith include the unity of science and religion, equality between different peoples and religions, the importance of education and tolerance, and the unity of world religions due to the oneness of God. Today it is estimated that over five million people follow the teachings of the Báb and Bahá’u’lláh worldwide.