Does it account for Daylight Saving Time?

Yes, our converter uses the IANA timezone database, which includes all current DST rules for every timezone in the world.

UTC (Coordinated Universal Time) is the primary time standard by which the world regulates clocks. All timezones are defined as offsets from UTC.

Can I compare multiple timezones at once?

Yes, you can add multiple cities or timezones and see the equivalent times side by side.

How many timezones are there in the world?

There are 38 distinct UTC offsets in use, ranging from UTC-12 to UTC+14. This includes half-hour (UTC+5:30 India, UTC+9:30 Australia) and 45-minute offsets (UTC+5:45 Nepal, UTC+8:45 Australia).

What is the International Date Line?

The International Date Line (IDL) runs roughly along the 180° meridian in the Pacific Ocean. When you cross it westward, you gain a day; crossing eastward, you lose a day.

Why do some timezones have 30 or 45 minute offsets?

Countries chose offsets that best matched their solar noon. India uses UTC+5:30 and Nepal uses UTC+5:45 because standard hourly offsets didn't align well with their geography.

Which country has the most timezones?

France has the most (12 timezones) due to overseas territories. Russia spans 11 timezones. The US has 6 (including Hawaii and Alaska).

GMT to IRST

+3h 30m

GMT

GMTSOURCE

UTC+01:00☀ DST active

HH12

MM00

12:00 (24-hr)

12 AM6 AM12 PM6 PM12 AM

IRST

UTC+03:30

HH03

MM30

15:30 (24-hr)

12 AM6 AM12 PM6 PM12 AM

Quick Reference

Time Conversion Table

GMT

IRST

12:00 AM

2:30 AM

2:00 AM

4:30 AM

4:00 AM

6:30 AM

6:00 AM

8:30 AM

8:00 AM

10:30 AM

10:00 AM

12:30 PM

12:00 PM

2:30 PM

2:00 PM

4:30 PM

4:00 PM

6:30 PM

6:00 PM

8:30 PM

8:00 PM

10:30 PM

10:00 PM

12:30 AM+1

Green rows indicate typical business hours (9 AM - 5 PM)

GMT and IRST on the World Map

The map below highlights the GMT (Greenwich Mean Time) and IRST (Iran Standard Time) timezone regions across the globe.

GMT Zone

→

IRST Zone

Explore all world timezones interactively →

GMT – Greenwich Mean Time

UTC+00:00

Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London. It is the same as UTC+00:00.

Countries in GMT

United KingdomIrelandIcelandPortugal (mainland)GhanaSenegalMaliMauritaniaGambiaGuineaSierra LeoneLiberiaIvory CoastBurkina FasoMorocco (historically)

Major Cities in GMT

LondonDublinLisbonAccraReykjavikEdinburghCasablancaDakarBamakoAbidjanConakryFreetownMonrovia

Key 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.
•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.

Daylight Saving:Yes – switches to BST

Learn more about GMT on Wikipedia

IRST – Iran Standard Time

UTC+03:30

Iran Standard Time (IRST) is the time zone for Iran, 3 hours and 30 minutes ahead of UTC.

Countries in IRST

Iran

Major Cities in IRST

TehranIsfahanMashhadTabrizShirazKaraj

Key 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).
•Tehran has a metropolitan population of over 16 million.

Daylight Saving:Yes – switches to IRDT

Learn more about IRST on Wikipedia

GMT vs IRST: Offsets, DST and Best Call Times

GMT runs on Greenwich Mean Time (GMT) at UTC+00:00. IRST runs on Iran Standard Time (IRST) at UTC+03:30. That puts GMT 3 hours 30 minutes ahead of IRST — a difference of +3h 30m at the current offsets.

In practice, when it is 9:00 AM in GMT it is 12:30 PM in IRST. Midnight in GMT is 3:30 AM in IRST. Neither zone observes daylight saving time, so the offset between them stays constant all year.

GMT to IRST time conversion table

GMT (GMT)	IRST (IRST)	Day
12:00 AM	3:30 AM	same day
6:00 AM	9:30 AM	same day
7:00 AM	10:30 AM	same day
8:00 AM	11:30 AM	same day
9:00 AM	12:30 PM	same day
12:00 PM	3:30 PM	same day
3:00 PM	6:30 PM	same day
5:00 PM	8:30 PM	same day
6:00 PM	9:30 PM	same day
9:00 PM	12:30 AM	next day

Why people convert GMT to IRST time

Scheduling a call from GMT to IRST: a 10:00 AM start in GMT lands at 1:30 PM in IRST, so you can confirm the slot without doing the arithmetic yourself.
Finding shared working hours: both GMT and IRST are inside the 9-to-5 working day between 9:00 AM and 1:30 PM GMT time (12:30 PM–5:00 PM IRST). That is roughly 4 hours 30 minutes of usable overlap.
Watching a live event or market open: GMT viewers need 12:30 PM in IRST to catch a 9:00 AM start there, and 8:30 PM if the event is anchored to GMT.

Always state the zone abbreviation, not just the hour. "3:00 PM GMT" is unambiguous; "3 PM" across a +3h 30m gap is not.
Block 9:00 AM–1:30 PM GMT as the recurring meeting window if you work primarily from GMT and need IRST colleagues present.

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 GMT and IRST

Both GMT and IRST sit inside the 9 AM – 5 PM working day between 9:00 AM–1:30 PM GMT, which is 12:30 PM–5:00 PM IRST. That gives roughly 4 hours and 30 minutes of shared time — the safest window for a live call or meeting.

Business hours overlap

GMT and IRST overlap for about 4 hours during the working day — enough for meetings if you avoid the edges of the window.

GMT is 3 hours 30 minutes ahead of IRST (GMT UTC+00:00 → IRST UTC+03:30). The shared working window is 9:00 AM–1:30 PM GMT. Remember to re-check around daylight-saving transitions.

🕐 Daylight Saving Time Info

GMT

☀ 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:

⏳

History of Timekeeping

From sundials to atomic clocks - 5000 years of measuring time

🌍

How Time Zones Work

UTC, offsets, and why zones don't follow straight lines

☀️

Daylight Saving Time

DST dates, which countries observe it, and the ongoing debate

Frequently Asked Questions

What is the time difference between GMT and IRST?

GMT (GMT, UTC+00:00) is 3 hours 30 minutes ahead of IRST (IRST, UTC+03:30). The gap is currently +3h 30m.

How do I convert GMT time to IRST time?

Add +3h 30m to GMT local time. For example, 9:00 AM in GMT is 12:30 PM 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 +3h 30m offset from GMT.

What is the best time to call IRST from GMT?

Call between 9:00 AM and 1:30 PM GMT — that maps to 12:30 PM–5:00 PM IRST and keeps both parties inside the working day.

Which is ahead, GMT or IRST?

GMT is 3 hours 30 minutes ahead of IRST. When it is 12:00 PM in GMT it is 3:30 PM in IRST.

Does daylight saving time affect the GMT–IRST difference?

Neither zone observes daylight saving time, so the +3h 30m offset between GMT and IRST is fixed all year.

Which other cities share GMT's time zone?

GMT also covers London, Dublin, Lisbon, Accra, Reykjavik, Edinburgh, Casablanca, Dakar and 5 more.

Which countries use GMT, GMT's zone?

GMT is used in United Kingdom, Ireland, Iceland, Portugal (mainland), Ghana, Senegal, Mali, Mauritania and 7 more.

Is there a day difference between GMT and IRST?

Not normally. The +3h 30m gap only pushes the date over for late-evening times.

What is the time difference between GMT and IRST?

IRST is +3h 30m from GMT.

What timezone is GMT in?

GMT operates on its local timezone.

What timezone is IRST in?

IRST operates on its local timezone.

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.