London to IRST
+2h 30mLondon
BSTSOURCEIRST
IRSTGreen rows indicate typical business hours (9 AM - 5 PM)
BST and IRST on the World Map
The map below highlights the BST (Greenwich Mean Time) and IRST (Iran Standard Time) timezone regions across the globe.
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.
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.
About London
WikipediaLondon, where Greenwich Mean Time (GMT) originates, is the world's leading financial center alongside New York. The city bridges European and American business hours.
Big Ben is actually the name of the bell inside the Elizabeth Tower, not the tower itself.
Understanding the +2h 30m Gap: London vs IRST
London runs on British Summer Time (BST) at UTC+01:00, currently observing daylight saving time. IRST runs on Iran Standard Time (IRST) at UTC+03:30. That puts London 2 hours 30 minutes ahead of IRST — a difference of +2h 30m at the current offsets.
In practice, when it is 9:00 AM in London it is 11:30 AM in IRST. Midnight in London is 2:30 AM in IRST.London observes daylight saving time while IRST does not, so the gap narrows or widens by an hour part of the year.
London to IRST time conversion table
| London (BST) | IRST (IRST) | Day |
|---|---|---|
| 12:00 AM | 2:30 AM | same day |
| 6:00 AM | 8:30 AM | same day |
| 7:00 AM | 9:30 AM | same day |
| 8:00 AM | 10:30 AM | same day |
| 9:00 AM | 11:30 AM | same day |
| 12:00 PM | 2:30 PM | same day |
| 3:00 PM | 5:30 PM | same day |
| 5:00 PM | 7:30 PM | same day |
| 6:00 PM | 8:30 PM | same day |
| 9:00 PM | 11:30 PM | same day |
Why people convert London to IRST time
- Scheduling a call from London to IRST: a 10:00 AM start in London lands at 12:30 PM in IRST, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both London and IRST are inside the 9-to-5 working day between 9:00 AM and 2:30 PM BST time (11:30 AM–5:00 PM IRST). That is roughly 5 hours 30 minutes of usable overlap.
- Keeping family and friends in sync: knowing that 8:00 PM in London is 10:30 PM in IRST makes it easy to avoid calling at 3 AM.
- Always state the zone abbreviation, not just the hour. "3:00 PM BST" is unambiguous; "3 PM" across a +2h 30m gap is not.
- Block 9:00 AM–2:30 PM BST as the recurring meeting window if you work primarily from London and need IRST colleagues present.
- London: Clocks fall back on Sun, Oct 25, 2026. Re-check this page after that date because the offset changes and so does the +2h 30m gap.
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.
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.
Best time to call between London and IRST
Both London and IRST sit inside the 9 AM – 5 PM working day between 9:00 AM–2:30 PM BST, which is 11:30 AM–5:00 PM IRST. That gives roughly 5 hours and 30 minutes of shared time — the safest window for a live call or meeting.
Business hours overlap
London and IRST share 5 hours of working-hours overlap (9:00 AM–2:30 PM BST), so scheduling a live meeting is straightforward.
London is 2 hours 30 minutes ahead of IRST (BST UTC+01:00 → IRST UTC+03:30). The shared working window is 9:00 AM–2:30 PM BST. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
London
☀ Currently in DST
Standard: UTC+00:00 · DST: UTC+01:00
Clocks fall back on Sun, Oct 25, 2026
IRST
Does not observe DST
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 London and IRST?
London (BST, UTC+01:00) is 2 hours 30 minutes ahead of IRST (IRST, UTC+03:30). The gap is currently +2h 30m.
How do I convert London time to IRST time?
Add +2h 30m to London local time. For example, 9:00 AM in London is 11:30 AM in IRST.
What time is it in IRST right now?
IRST uses IRST at UTC+03:30. Use the live converter at the top of this page — it updates in real time and already accounts for the +2h 30m offset from London.
What is the best time to call IRST from London?
Call between 9:00 AM and 2:30 PM BST — that maps to 11:30 AM–5:00 PM IRST and keeps both parties inside the working day.
Which is ahead, London or IRST?
London is 2 hours 30 minutes ahead of IRST. When it is 12:00 PM in London it is 2:30 PM in IRST.
Do London and IRST use different time zones?
London (UK) uses BST at UTC+01:00, while IRST uses IRST at UTC+03:30. The IANA identifiers are Europe/London and Asia/Tehran.
Does daylight saving time affect the London–IRST difference?
Yes at the moment: London 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 London's time zone?
BST also covers London, Dublin, Lisbon, Accra, Reykjavik, Edinburgh, Casablanca, Dakar and 5 more.
Which countries use BST, London's zone?
BST is used in United Kingdom, Ireland, Iceland, Portugal (mainland), Ghana, Senegal, Mali, Mauritania and 7 more.
Is there a day difference between London and IRST?
Not normally. The +2h 30m gap only pushes the date over for late-evening times.
What is the time difference between London and IRST?
IRST is +2h 30m from London.
What timezone is London in?
London, where Greenwich Mean Time (GMT) originates, is the world's leading financial center alongside New York. The city bridges European and American business hours.
What timezone is IRST in?
IRST operates on its local timezone.
What are the business hours in London?
Standard business hours in London are 9:00 AM - 5:00 PM GMT.
Which countries use GMT (Greenwich Mean Time)?
GMT is used in United Kingdom, Ireland, Iceland, Portugal (mainland), Ghana, Senegal, and 9 more countries.
Does GMT observe daylight saving time?
Yes, GMT switches to BST during summer months.
What are some interesting facts about GMT?
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.
Which cities are in the IRST timezone?
Major cities in the IRST timezone include Tehran, Isfahan, Mashhad, Tabriz, Shiraz, Karaj.
What is the UTC offset for IRST?
Iran Standard Time (IRST) is at UTC+03:30. During daylight saving time, it shifts to IRDT.
What should I know about the IRST timezone?
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).
When is it midnight in London, what time is it in IRST?
When it is 12:00 AM (midnight) in London (GMT), it is +2h 30m later in IRST (IRST).
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