Iran Daylight Time (IRDT)
UTC offset: +04:30
Standard offset: +03:30 (IRST)
IANA identifier: Asia/Tehran
Abbreviation: IRDT
Population: approximately 88 million
DST observed: Yes (Persian calendar-based transitions)
Iran Daylight Time advances the country's clocks one hour from IRST (UTC+03:30) to UTC+04:30. Iran is one of a handful of countries with a half-hour offset, and one of the few that applies DST on top of it. The transitions follow the Persian (Solar Hijri) calendar rather than Gregorian dates, typically beginning around March 21-22 (1 Farvardin, the start of the Iranian New Year) and ending around September 21-22 (the autumnal equinox).
This means DST in Iran begins almost exactly at the spring equinox and ends at the fall equinox, a more astronomically logical system than the arbitrary Sundays used in the US and EU.
The Half-Hour Offset
Iran's standard offset of +03:30 places it 30 minutes ahead of the Arabian Peninsula (Gulf states at +03:00) and 30 minutes behind Afghanistan (+04:30 standard). The half-hour shift was adopted in 1945 to better align official time with solar noon in Tehran (at roughly 51.5°E longitude, solar noon occurs around 12:07 on standard time).
The IRDT offset of +04:30 is shared with Afghanistan's standard time, which doesn't observe DST.
Tehran
The capital (~9 million, metro ~15 million) sprawls across a north-south slope below the Alborz Mountains. Northern Tehran is affluent, cooler, and closer to ski resorts (Dizin, Tochal). Southern Tehran is industrial and working-class. Traffic is legendary. Pollution traps in the basin between mountain ranges.
Business hours: typically 8:00 a.m. to 4:00 p.m. Saturday through Wednesday. Thursday is a half-day. Friday is the weekly holiday. Iran's work week runs Saturday through Thursday (or Wednesday), not Monday through Friday.
Mashhad
Iran's second-largest city (~3.3 million) and the country's holiest. The Imam Reza Shrine draws 20+ million pilgrims annually, making Mashhad one of the most-visited pilgrimage sites in the Islamic world. The shrine complex is enormous, covering several city blocks with courtyards, mosques, museums, and libraries.
Isfahan
Perhaps Iran's most beautiful city (~2 million). Naqsh-e Jahan Square (one of the world's largest public squares), the Shah Mosque, and the 33-arch Si-o-se-pol bridge are UNESCO-recognized. Isfahan was the Safavid capital (1598-1722) and retains that era's architectural grandeur.
Nowruz and DST
The DST transition coincides almost exactly with Nowruz (Persian New Year), the biggest holiday in the Iranian calendar. This means the clock change happens during a two-week holiday period when most people aren't working regular schedules anyway, minimizing disruption. It's an elegant alignment.
Sanctions and Scheduling
International sanctions and diplomatic isolation mean Iran's business connections differ from neighbors. Trading partners include China, India, Turkey, Russia, and Iraq. The +04:30 offset creates scheduling challenges:
- With China (+08:00): 3.5 hours ahead
- With India (+05:30): 1 hour ahead (summer)
- With Turkey (+03:00): 1.5 hours ahead
- With Russia/Moscow (+03:00): 1.5 hours ahead
- With EU (CEST, +02:00): 2.5 hours ahead
- With US East (EDT, -04:00): 8.5 hours ahead
The half-hour offset ensures no time zone aligns cleanly with Iran, always producing .5-hour gaps.
Scheduling
At UTC+04:30 (IRDT):
- Gulf States (AST): 1.5 hours behind
- India: 1 hour ahead
- Turkey: 1.5 hours behind
- UK (BST): 3.5 hours behind
- Pakistan: 30 minutes ahead
Neighboring Zones
| Zone | Offset | Difference from IRDT |
|---|---|---|
| Gulf States (UAE, etc.) | UTC+04:00 | 30 min behind |
| Afghanistan | UTC+04:30 | Same |
| Pakistan | UTC+05:00 | 30 min ahead |
| Turkey | UTC+03:00 | 1.5 hours behind |
| India | UTC+05:30 | 1 hour ahead |
| Iraq | UTC+03:00 | 1.5 hours behind |
Technical Identifiers
- Asia/Tehran (IANA canonical)
- IRDT (Iran Daylight Time)
- IRST (winter: Iran Standard Time, UTC+03:30)
- Windows: "Iran Standard Time"
- DST rule: approximately 1 Farvardin to 1 Mehr (Persian calendar)
- Military/aviation: none standard (half-hour zones are unusual)
Quick Reference
| Attribute | Value |
|---|---|
| UTC offset (summer) | +04:30 |
| UTC offset (winter) | +03:30 |
| DST observed | Yes (Persian calendar) |
| IANA zone | Asia/Tehran |
| Population | ~88 million |
| Capital | Tehran |
| Work week | Saturday-Thursday |
| DST start | ~March 21 (Nowruz) |
| Half-hour offset | Yes (since 1945) |
| Same summer offset as | Afghanistan (standard) |