Tehran, Iran · UTC+3:30 ☆

Tehran is a city of 15 million people in a bowl ringed by the Alborz Mountains, and it runs on one of the world’s more unusual clocks. Iran Standard Time sits at UTC+3:30, a half-hour offset that puts Tehran 30 minutes out of step with both its immediate neighbors and the usual whole-hour timezone grid.

The offset has historical roots. Iran set its standard time based on the meridian running through Tehran, which falls near 52.5 degrees east longitude, the midpoint between UTC+3 and UTC+4. Rather than round to a whole hour, Iran kept the half-hour. The tradition survived the Islamic Revolution and remains today.

Nowruz, DST, and the Persian calendar

Iran also observes daylight saving time, clocks moving to UTC+4:30 in summer. The switchover follows the Persian calendar rather than the Gregorian, beginning at the vernal equinox (Nowruz, Persian New Year) around March 20-21. This means the DST changeover and the new year celebration happen simultaneously, one of the more culturally dense timezone transitions on the calendar.

Tehran’s morning rush begins early by regional standards. The city’s traffic density, among the worst in the world, means commuters allow enormous time buffers. The actual hour of departure often matters less than the estimated hours of delay.

9am in Tehran is 5:30am in London. Isfahan shares Iran Standard Time.

Sources

• IANA Time Zone Database - Asia/Tehran
• Statistical Centre of Iran