"The Iran Population counter shows a continuously updated estimate of the current population of the Islamic Republic of Iran delivered by Worldometers' RTS algorithm, which processes data collected from the United Nations Population Division. Year: as of July 1 of the year indicated. Population: Overall total population (both sexes and all ages) in the country as of July 1 of the year indicated, as estimated by the United Nations, Department of Economic and Social Affairs, Population Division. World Population Prospects: The 2017 Revision. This counter was counted at the end first six months of the year. From 1955 to 2015, the dataset was updated each 5 years once, and from 2015 to 2018 the counter was updated each year. "

http://www.worldometers.info/world-population/iran-population/