Capital: Tehran · Single time zone (IRST, UTC+3:30, one of the world's few half-hour offsets) · a Shia-majority country where two distinct calculation conventions are both genuinely in use.
Iran is unusual on this list because it doesn't have one single obvious calculation convention. The Institute of Geophysics at the University of Tehran publishes a mainstream astronomical method broadly compatible with Sunni calculation practice, while the Shia Ithna-Ashari, Leva Institute, Qum convention reflects Twelver Shia fiqh specifically — and since Iran is overwhelmingly Shia-majority, this second method is the one most Iranian mosques and religious calendars actually follow day to day.
The main practical difference is Maghrib: the Shia Ithna-Ashari convention delays it slightly past sunset, following the Shia position that the reddish afterglow in the eastern sky must fade first.
Iran's mainstream astronomical method, from the Institute of Geophysics at the University of Tehran, is broadly compatible with Sunni calculation practice, while the Shia Ithna-Ashari, Leva Institute, Qum convention reflects Twelver Shia fiqh, which most of Iran's population follows.
The most noticeable difference is Maghrib: the Shia Ithna-Ashari convention delays Maghrib slightly past sunset rather than starting it at sunset itself, reflecting the position that redness in the eastern sky must fade first.
The Shia Ithna-Ashari, Leva Institute, Qum convention is built specifically around Twelver Shia jurisprudence and is the one followed in most Iranian mosques and religious calendars.
No — the calculation is based on the sun's position at each location, not the clock offset; Iran's half-hour offset just changes how that solar time is displayed on a clock face.