IRST to United Kingdom
-2h 30mIRST
IRSTSOURCEUnited Kingdom
BSTGreen rows indicate typical business hours (9 AM - 5 PM)
IRST and BST on the World Map
The map below highlights the IRST (Iran Standard Time) and BST (Greenwich Mean Time) timezone regions across the globe.
IRST – Iran Standard Time
UTC+03:30Iran Standard Time (IRST) is the time zone for Iran, 3 hours and 30 minutes ahead of UTC.
- •IRST is one of only a few time zones with a 30-minute offset.
- •Iran observes daylight saving time, switching to IRDT (UTC+04:30).
- •Tehran has a metropolitan population of over 16 million.
GMT – Greenwich Mean Time
UTC+00:00Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London. It is the same as UTC+00:00.
- •GMT is based on the Prime Meridian (0° longitude) passing through Greenwich, London.
- •The Royal Observatory in Greenwich has been the reference point for GMT since 1884.
- •GMT and UTC are often used interchangeably, but UTC is based on atomic clocks.
- •Iceland uses GMT year-round and never observes daylight saving time.
- •The UK switches from GMT to BST (British Summer Time) in late March each year.
Understanding the -2h 30m Gap: IRST vs United Kingdom
IRST runs on Iran Standard Time (IRST) at UTC+03:30. United Kingdom runs on British Summer Time (BST) at UTC+01:00, also currently on daylight saving time. That puts IRST 2 hours 30 minutes behind United Kingdom — a difference of -2h 30m at the current offsets.
In practice, when it is 9:00 AM in IRST it is 6:30 AM in United Kingdom. Midnight in IRST is 9:30 PM in United Kingdom.United Kingdom observes daylight saving time while IRST does not, so the gap narrows or widens by an hour part of the year.
IRST to United Kingdom time conversion table
| IRST (IRST) | United Kingdom (BST) | Day |
|---|---|---|
| 12:00 AM | 9:30 PM | previous day |
| 6:00 AM | 3:30 AM | same day |
| 7:00 AM | 4:30 AM | same day |
| 8:00 AM | 5:30 AM | same day |
| 9:00 AM | 6:30 AM | same day |
| 12:00 PM | 9:30 AM | same day |
| 3:00 PM | 12:30 PM | same day |
| 5:00 PM | 2:30 PM | same day |
| 6:00 PM | 3:30 PM | same day |
| 9:00 PM | 6:30 PM | same day |
Why people convert IRST to United Kingdom time
- Scheduling a call from IRST to United Kingdom: a 10:00 AM start in IRST lands at 7:30 AM in United Kingdom, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both IRST and United Kingdom are inside the 9-to-5 working day between 11:30 AM and 5:00 PM IRST time (9:00 AM–2:30 PM BST). That is roughly 5 hours 30 minutes of usable overlap.
- Watching a live event or market open: IRST viewers need 6:30 AM in United Kingdom to catch a 9:00 AM start there, and 2:30 AM if the event is anchored to IRST.
- Always state the zone abbreviation, not just the hour. "3:00 PM IRST" is unambiguous; "3 PM" across a -2h 30m gap is not.
- Block 11:30 AM–5:00 PM IRST as the recurring meeting window if you work primarily from IRST and need United Kingdom colleagues present.
- United Kingdom: Clocks fall back on Sun, Oct 25, 2026. Any meeting series spanning that date will shift by an hour in local time.
About IRST (Iran Standard Time)
Iran Standard Time (IRST) is one of the few time zones with a 30-minute offset. Iran observes daylight saving time (IRDT, UTC+04:30) from late March to late September. Tehran, the capital, is one of the largest cities in the Middle East.
About GMT (Greenwich Mean Time)
Greenwich Mean Time (GMT) is the clock time at the Royal Observatory in Greenwich, London, which sits on the Prime Meridian (0° longitude). GMT serves as the reference point from which all other time zones are calculated. The United Kingdom uses GMT during winter months and switches to British Summer Time (BST, UTC+01:00) from late March to late October. Several West African nations use GMT year-round. GMT is often used interchangeably with UTC (Coordinated Universal Time), although technically they are different – UTC is based on atomic clocks while GMT is based on Earth's rotation.
Best time to call between IRST and United Kingdom
Both IRST and United Kingdom sit inside the 9 AM – 5 PM working day between 11:30 AM–5:00 PM IRST, which is 9:00 AM–2:30 PM BST. That gives roughly 5 hours and 30 minutes of shared time — the safest window for a live call or meeting.
Business hours overlap
IRST and United Kingdom share 5 hours of working-hours overlap (11:30 AM–5:00 PM IRST), so scheduling a live meeting is straightforward.
IRST is 2 hours 30 minutes behind United Kingdom (IRST UTC+03:30 → BST UTC+01:00). The shared working window is 11:30 AM–5:00 PM IRST. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
IRST
Does not observe DST
United Kingdom
☀ Currently in DST
Standard: UTC+00:00 · DST: UTC+01:00
Clocks fall back on Sun, Oct 25, 2026
Learn More About Time
Dive deeper into the fascinating world of timekeeping, time zones, and how they shape our global society:
Frequently Asked Questions
What is the time difference between IRST and United Kingdom?
IRST (IRST, UTC+03:30) is 2 hours 30 minutes behind United Kingdom (BST, UTC+01:00). The gap is currently -2h 30m.
How do I convert IRST time to United Kingdom time?
Add -2h 30m to IRST local time. For example, 9:00 AM in IRST is 6:30 AM in United Kingdom.
What time is it in United Kingdom right now?
United Kingdom uses BST at UTC+01:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -2h 30m offset from IRST.
What is the best time to call United Kingdom from IRST?
Call between 11:30 AM and 5:00 PM IRST — that maps to 9:00 AM–2:30 PM BST and keeps both parties inside the working day.
Which is behind, IRST or United Kingdom?
IRST is 2 hours 30 minutes behind United Kingdom. When it is 12:00 PM in IRST it is 9:30 AM in United Kingdom.
Do IRST and United Kingdom use different time zones?
IRST uses IRST at UTC+03:30, while United Kingdom (United Kingdom) uses BST at UTC+01:00. The IANA identifiers are Asia/Tehran and Europe/London.
Does daylight saving time affect the IRST–United Kingdom difference?
Yes at the moment: United Kingdom is on daylight saving time and IRST is not, so the -2h 30m gap shifts by an hour when exactly one of them changes clocks.
Which other cities share IRST's time zone?
IRST also covers Tehran, Isfahan, Mashhad, Tabriz, Shiraz, Karaj.
Which countries use IRST, IRST's zone?
IRST is used in Iran.
Is there a day difference between IRST and United Kingdom?
Not normally. The -2h 30m gap only pushes the date over the previous day.
What is the time difference between IRST and United Kingdom?
United Kingdom is -2h 30m from IRST.
What timezone is IRST in?
IRST operates on its local timezone.
What timezone is United Kingdom in?
United Kingdom operates on its local timezone.
Which countries use IRST (Iran Standard Time)?
IRST is used in Iran.
Does IRST observe daylight saving time?
Yes, IRST switches to IRDT during summer months.
What are some interesting facts about IRST?
IRST is one of only a few time zones with a 30-minute offset. Iran observes daylight saving time, switching to IRDT (UTC+04:30).
Which cities are in the GMT timezone?
Major cities in the GMT timezone include London, Dublin, Lisbon, Accra, Reykjavik, Edinburgh, Casablanca, Dakar.
What is the UTC offset for GMT?
Greenwich Mean Time (GMT) is at UTC+00:00. During daylight saving time, it shifts to BST.
What should I know about the GMT timezone?
GMT is based on the Prime Meridian (0° longitude) passing through Greenwich, London. The Royal Observatory in Greenwich has been the reference point for GMT since 1884.
When is it midnight in IRST, what time is it in United Kingdom?
When it is 12:00 AM (midnight) in IRST (IRST), it is -2h 30m later in United Kingdom (GMT).
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