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).

IRST to GMT

-3h 30m

IRST

IRSTSOURCE

UTC+03:30

HH12

MM00

12:00 (24-hr)

12 AM6 AM12 PM6 PM12 AM

GMT

UTC+01:00☀ DST active

HH08

MM30

08:30 (24-hr)

12 AM6 AM12 PM6 PM12 AM

Quick Reference

Time Conversion Table

IRST

GMT

12:00 AM

9:30 PM-1

2:00 AM

11:30 PM-1

4:00 AM

1:30 AM

6:00 AM

3:30 AM

8:00 AM

5:30 AM

10:00 AM

7:30 AM

12:00 PM

9:30 AM

2:00 PM

11:30 AM

4:00 PM

1:30 PM

6:00 PM

3:30 PM

8:00 PM

5:30 PM

10:00 PM

7:30 PM

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

IRST and GMT on the World Map

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

IRST Zone

→

GMT Zone

Explore all world timezones interactively →

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 – 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 vs GMT: Offsets, DST and Best Call Times

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

In practice, when it is 9:00 AM in IRST it is 5:30 AM in GMT. Midnight in IRST is 8:30 PM in GMT. Neither zone observes daylight saving time, so the offset between them stays constant all year.

IRST to GMT time conversion table

IRST (IRST)	GMT (GMT)	Day
12:00 AM	8:30 PM	previous day
6:00 AM	2:30 AM	same day
7:00 AM	3:30 AM	same day
8:00 AM	4:30 AM	same day
9:00 AM	5:30 AM	same day
12:00 PM	8:30 AM	same day
3:00 PM	11:30 AM	same day
5:00 PM	1:30 PM	same day
6:00 PM	2:30 PM	same day
9:00 PM	5:30 PM	same day

Why people convert IRST to GMT time

Scheduling a call from IRST to GMT: a 10:00 AM start in IRST lands at 6:30 AM in GMT, so you can confirm the slot without doing the arithmetic yourself.
Finding shared working hours: both IRST and GMT are inside the 9-to-5 working day between 12:30 PM and 5:00 PM IRST time (9:00 AM–1:30 PM GMT). That is roughly 4 hours 30 minutes of usable overlap.
Booking travel or deliveries: tracking GMT local time against IRST keeps pickup windows and arrival estimates honest across the -3h 30m offset.

Always state the zone abbreviation, not just the hour. "3:00 PM IRST" is unambiguous; "3 PM" across a -3h 30m gap is not.
Block 12:30 PM–5:00 PM IRST as the recurring meeting window if you work primarily from IRST and need GMT colleagues present.

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 GMT

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

Business hours overlap

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

IRST is 3 hours 30 minutes behind GMT (IRST UTC+03:30 → GMT UTC+00:00). The shared working window is 12:30 PM–5:00 PM IRST. Remember to re-check around daylight-saving transitions.

🕐 Daylight Saving Time Info

IRST

Does not observe DST

GMT

☀ 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:

⏳

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 IRST and GMT?

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

How do I convert IRST time to GMT time?

Add -3h 30m to IRST local time. For example, 9:00 AM in IRST is 5:30 AM in GMT.

What time is it in GMT right now?

GMT uses GMT at UTC+00:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -3h 30m offset from IRST.

What is the best time to call GMT from IRST?

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

Which is behind, IRST or GMT?

IRST is 3 hours 30 minutes behind GMT. When it is 12:00 PM in IRST it is 8:30 AM in GMT.

Does daylight saving time affect the IRST–GMT difference?

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

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 GMT?

Not normally. The -3h 30m gap only pushes the date over the previous day.

What is the time difference between IRST and GMT?

GMT is -3h 30m from IRST.

What timezone is IRST in?

IRST operates on its local timezone.

What timezone is GMT in?

GMT 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.