What is the time difference between IRST and GMT?

Greenwich Mean Time (GMT) is 2 hours and 30 minutes behind Iran Standard Time (IRST). IRST uses a UTC offset of UTC+3:30, while GMT uses UTC+1. For example, when it's 9:00 AM in IRST, it's 6:30 AM in GMT. Note that this difference may shift by one hour during daylight saving time transitions if GMT observes DST. Use the conversion table above to see the exact time for each hour of the day.

How do I convert IRST to GMT?

To convert IRST to GMT, subtract 2 hours and 30 minutes from the IRST time. For example, 9:00 AM IRST is 6:30 AM GMT, and 5:00 PM IRST is 2:30 PM GMT. Keep in mind that during daylight saving time transitions, the offset between these timezones may temporarily change by one hour. You can also use the interactive converter above for quick, accurate results.

What time is it in GMT when it's noon in IRST?

When it's 12:00 PM (noon) in IRST, it's 9:30 AM in GMT. This is because GMT is 2 hours and 30 minutes behind IRST. Similarly, when it's 6:00 PM in IRST, it's 3:30 PM in GMT. During daylight saving time transitions, these times may shift by one hour, so always verify the current offset. The color-coded conversion table above shows every hour mapped between both timezones.

How many hours behind is GMT from IRST?

GMT is 2 hours and 30 minutes behind IRST. This means when it's 9:00 AM in IRST, it's 6:30 AM in GMT, and when it's midnight in IRST, it's 9:30 PM in GMT. The exact difference can vary by one hour during daylight saving time transitions. The conversion table above provides a complete hour-by-hour mapping.

Is GMT ahead or behind IRST?

GMT is behind IRST by 2 hours and 30 minutes. Clocks in GMT show an earlier time than IRST, meaning the day starts later in GMT relative to IRST. For example, when it's noon in IRST, it's still 9:30 AM in GMT. This gap may change by one hour during DST transitions.

Does IRST observe daylight saving time?

No, Iran Standard Time does not observe daylight saving time. The UTC offset of UTC+3:30 remains the same year-round, which simplifies time conversions. Regions using IRST keep their clocks unchanged regardless of the season.

Does GMT observe daylight saving time?

Yes, Greenwich Mean Time observes daylight saving time. During DST, the abbreviation changes to BST and clocks move forward by one hour, typically in spring. Clocks then fall back in autumn, returning to standard GMT time. This means the UTC offset for GMT shifts between two values depending on the season. Check our DST change calendar for exact transition dates that may affect your IRST to GMT conversions.

What is the best time to call from IRST to GMT?

The best time for a call between IRST and GMT is during overlapping business hours (9 AM – 5 PM) in both timezones. To reach someone in GMT during their work day, call between 11:30 AM and 7:30 PM your IRST time. Avoid calling too early or late, as the 2 hours and 30 minutes difference means your evening could be their early morning. Check the color-coded conversion table above — green hours indicate business hours in both zones, making it easy to find the ideal time.

When does daylight saving time change in GMT?

Daylight saving time transitions vary by year and region. Greenwich Mean Time observes DST, which typically shifts clocks forward by one hour in spring ("spring forward") and back in fall ("fall back"). During these transition periods, the time difference between IRST and GMT may temporarily change by one hour, which can cause confusion for scheduled meetings or calls. It's important to double-check your conversions around transition dates, especially if the two timezones switch on different dates. Check our DST change calendar for exact transition dates in the current year.

Do IRST and GMT ever have the same time?

No, IRST and GMT never show the same time because their base UTC offsets are different. However, because GMT observes daylight saving time and IRST does not, the time difference between them changes by one hour during DST transitions. This means the gap narrows or widens depending on the season, but the two clocks never align. Always verify the current offset around DST transition dates to avoid scheduling errors.

IRST to GMT Converter

Convert Iran Standard Time to Greenwich Mean Time. See the hour-by-hour conversion table below.

Upcoming DST Change

UK Time (BST) will fall back on October 25. Clocks will shift by 1 hour (BST → GMT).

View all DST changes

Timezone Details

Tehran

9:11 AM

Monday, October 19, 2026

Tehran (UTC+03:30)

Greenwich Mean Time

6:41 AM

Monday, October 19, 2026

BST (UTC+01:00)

Difference: -2h 30m

BST DST: Yes (BST)

24-Hour Overview

Tehran — 24-hour overview

12a12a

3a3a

6a6a

9a9a

10a

11a

12p12p

3p3p

6p6p

9p9p

10p

11p

NightMorningBusinessEvening

BST — 24-hour overview

9p9p

10p

11p

12a12a

3a3a

6a6a

9a9a

10a

11a

12p12p

3p3p

6p6p

NightMorningBusinessEvening

Frequently Asked Questions

Related Conversions

GMT to IRST EST to GMT GMT to EST PST to GMT GMT to PST GMT to IST IST to GMT GMT to CET CET to GMT

Cities in These Timezones

IRST Cities

Tehran

GMT Cities

London Manchester Edinburgh

More Tools

Compare IRST & GMT Plan a Meeting (IRST & GMT)See on Map

Learn More

How Time Zones Work Understanding DST Timezone Abbreviations

External Resources

Greenwich Mean Time on Wikipedia IANA Time Zone Database