Studies project that Iran's rate of population growth will continue to slow until it stabilises above 100 million by 2050.

In addition to its international migration pattern, Iran also exhibits one of the steepest urban growth rates in the world according to the UN humanitarian information unit.

[25] According to a study through the Australian National University, there are both micro and macro factors affecting the fertility rate in Iran, including education, economics, and culture.

The cross-sectional cohort study examined four provinces in Iran (Gilan, Sistan & Baluchistan, West Azerbaijan, and Yazd) and found that trends show that women in all four provinces are choosing to have fewer children compared to the women born in the earlier cohorts.

[26] Other sources also suggest that delayed marriage and a tendency to limit fertility are factors affecting the decline of TFR.

[28] In response, Iranian policymakers have attempted to limit these factors by restricting access to contraceptives and surgeries that reduce fertility.

[29] Sex ratio Life expectancy at birth Iran is a mosaic of diverse ethnic groups, contrary to popular belief that all Iranians are "just Persian".

[36] Among them, U3b3 lineages appear to be restricted to populations of Iran and the Caucasus, while the sub-cluster U3b1a is common in the whole Near East region.

[36] In Iran outliers in the Y-chromosomes and Mitochondrial DNA gene pool are consisted of the north Iranian ethnicities, such as the Gilaks and Mazandarani's, whose genetic build up including chromosomal DNA are nearly identical to the major South Caucasian ethnicities, namely the Georgians, Armenians and Azerbaijani's.

Other outliers are made by the Baloch people, representing a mere 1–2% of the total Iranian population, who have more patrilinial and mitochondrial DNA lines leaning towards northwest South Asian ethnic groups.

Levels of genetic variation in Iranian populations are comparable to the other groups from the Caucasus, Anatolia and Europe.

Certain South Asians (specifically the Parsi minority) showed the highest affinity with Iranians, inline with their ethnic history.

On a global scale, Iranians display their highest affinity with other "West Eurasian" populations (such as Europeans or South Asians, but also Latin Americans), while Sub-Saharan Africans and East Asians showed large degrees of differentiation with Iranians.

[37] The largest linguistic group comprises speakers of Iranian languages, like modern Persian, Kurdish, Gilaki, Mazandarani, Luri, Talysh, and Balochi.

However, significant pockets do exist spread over the country, and they are the second-largest Caucasus-derived group in the nation after the Georgians.

[38][39] Jews have had a continuous presence in Iran since the time of Cyrus the Great of the Achaemenid Empire.

According to the Tehran Jewish Committee, the Jewish population of Iran was (more recently) estimated at 25,000 to 35,000, of which approximately 15,000 are in Tehran with the rest residing in Hamadan, Shiraz, Isfahan, Kermanshah, Yazd, Kerman, Rafsanjan, Borujerd, Sanandaj, Tabriz and Urmia.

[40] The CIA World Factbook (which is based on 2013 statistics) gives the following numbers for the languages spoken in Iran today: Persian, Luri, Gilaki and Mazandarani 66%; Azerbaijani and other Turkic languages 18%; Kurdish 10%; Arabic 2%; Balochi 2%; others 2% (Armenian, Georgian, Circassian, Assyrian, etc.).

[41] According to anthropologist Brian Spooner, around half of Iran's population uses a language other than Persian at home and in informal public situations.

In the 20th to 21st centuries, there has been limited immigration to Iran from Turkey, Iraq (especially huge numbers during the 1970s known as Moaveds), Afghanistan (mostly arriving as refugees in 1978), Lebanon (especially in Qom, though a Lebanese community has been present in the nation for centuries), India (mostly arriving temporarily during the 1950s to 1970s, typically working as doctors, engineers, and teachers), Korea (mostly in the 1970s as labour migrants), China (mostly since the 2000s working in engineering or business projects), and Pakistan, partly due to labour migrants and partly to Balochi ties across the Iranian-Pakistani border.

[61] Other metropolises that have large Iranian populations include Dubai with 300,000 Iranians, Vancouver, London, Toronto, San Francisco Bay Area, Washington D.C., Buenos Aires, Mexico City, Stockholm, Berlin, Hamburg and Frankfurt.

Likely the ancestors of modern Tats settled in South Caucasus when the Sassanid Empire from the 3rd to 7th centuries built cities and founded military garrisons to strengthen their positions in this region.

Indian census data (2001) records 69,601 Parsis in India, with a concentration in and around the city of Mumbai (previously known as Bombay).

Unlike the Parsis, they speak a Dari dialect, the language spoken by the Iranian Zoroastrians in Yazd and Kerman.