The U.S. government estimates the population at 84 million (midyear 2019). Muslims are estimated to constitute 99.4 percent of the population, of which 90-95 percent are Shia, and 5-10 percent are Sunni, mostly Turkmen, Arabs, Baluchis, and Kurds living in the northeast, southwest, southeast, and northwest provinces, respectively. Afghan refugees, economic migrants, and displaced persons also make up a significant Sunni population, but accurate statistics on the breakdown of the Afghan refugee population between Sunni and Shia are unavailable. There are no official statistics available on the number of Muslims who practice Sufism, although unofficial reports estimate several million.

According to U.S. government estimates, groups constituting the remaining less than 1 percent of the population include Baha’is, Christians, Jews, Sabean-Mandaeans, Zoroastrians, and Yarsanis. The three largest non-Muslim minorities are Baha’is, Christians, and Yarsanis.

According to Human Rights Watch data, Baha’is number at least 300,000.

The government Statistical Center of Iran reports there are 117,700 Christians in the country. Some estimates, however, suggest there may be many more than actually reported. According to World Christian Database statistics, there are approximately 547,000 Christians. Elam Ministries, a Christian organization, estimates there could be between 300,000 and one million.

Estimates by the Assyrian Church of the total Assyrian and Chaldean Christian population put their combined number at 7,000. There are also Protestant denominations, including evangelical groups, but there is no authoritative data on their numbers. Christian groups outside the country disagree on the size of the Protestant community, with some estimates citing figures lower than 10,000, and others, such as Open Doors USA, citing numbers above 800,000. Many Protestants and converts to Christianity from Islam reportedly practice in secret.

There is no official count of Yarsanis, but HRANA and CHRI estimate there are up to two million. Yarsanis are mainly located in Loristan and the Kurdish regions.

According to recent estimates from Armenian Christians who maintain contact with the Iranian Christian community in the country, their current numbers are approximately 40,000 to 50,000 – significantly reduced from a peak of approximately 300,000 prior to 1979. The number of Roman Catholics in the country is estimated to be 21,000.

According to Zoroastrian groups and the government-run Statistical Center of Iran, the population includes approximately 25,000 Zoroastrians.

According to the Tehran Jewish Committee, the population includes approximately 9,000 Jews, while representatives from the Jewish community in the country estimated their number at 15,000 during a 2018 PBS News Hour interview.

The population, according to one international NGO, includes 5,000-10,000 Sabean-Mandaeans.

According to the 2011 census, the number of individuals who are areligious rose by 20 percent between 2006 and 2011, which supports observations by academics and others that the number of atheists, agnostics, nonbelievers, and religiously unaffiliated living in the country is growing. Often these groups, however, do not publicly identify, as documented by Amnesty International’s (AI) report on the country, because those who profess atheism are at risk of arbitrary detention, torture, and the death penalty for “apostasy.”

The U.S. government estimates the country’s total population at 33.6 million (midyear 2019 estimate), including more than 12 million foreign residents. Between 85 and 90 percent of the approximately 20 million citizens are Sunni Muslims.

Shia Muslims constitute 10 to 12 percent of the citizen population and at least one-quarter of the Eastern Province’s population. Approximately 80 percent of Shia are “Twelvers” (Shia who recognize 12 imams) and are primarily located in the Eastern Province. The Nakhawala, or “Medina Shia,” are also Twelvers and reside in small numbers in the western Hejaz region. Estimates place their numbers at approximately 1,000. Twelver Shia adhere to the Ja’afari school of jurisprudence. Most of the remaining Shia are Sulaimani Ismailis, also known as “Seveners” (those who branched off from the Twelvers to follow Isma’il ibn Ja’afar as the Seventh Imam). Seveners number approximately 500,000 and reside primarily in Najran Province, where they probably constitute a majority of the province’s inhabitants. Another branch of Sevener Shia, the Bohra Ismailis, probably number at least a few hundred, most of whom are of South Asian origin. Pockets of Zaydis, members of another branch of Shia Islam, numbering a total of approximately 20,000, reside primarily in the provinces of Jizan and Najran along the border with Yemen.

Foreign embassies indicate the noncitizen population, including many undocumented migrants, is mostly Muslim. According to a 2010 survey by the Pew Research Center, of the country’s total population (including foreigners), there were approximately 25.5 million Muslims, 1.2 million Christians (including Eastern Orthodox, Protestants, and Roman Catholics); 310,000 Hindus; 180,000 religiously unaffiliated (including atheists, agnostics, and individuals who did not identify with any particular religion); 90,000 Buddhists; 70,000 followers of folk religions; and 70,000 adherents of other religions.