What is the time difference between GMT and IRST?

Iran Standard Time (IRST) is 2 hours and 30 minutes ahead of Greenwich Mean Time (GMT). GMT uses a UTC offset of UTC+1, while IRST uses UTC+3:30. For example, when it's 9:00 AM in GMT, it's 11:30 AM in IRST. 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 GMT to IRST?

To convert GMT to IRST, add 2 hours and 30 minutes to the GMT time. For example, 9:00 AM GMT is 11:30 AM IRST, and 5:00 PM GMT is 7:30 PM IRST. 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 IRST when it's noon in GMT?

When it's 12:00 PM (noon) in GMT, it's 2:30 PM in IRST. This is because IRST is 2 hours and 30 minutes ahead of GMT. Similarly, when it's 6:00 PM in GMT, it's 8:30 PM in IRST. 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 ahead is IRST from GMT?

IRST is 2 hours and 30 minutes ahead of GMT. This means when it's 9:00 AM in GMT, it's 11:30 AM in IRST, and when it's midnight in GMT, it's 2:30 AM in IRST. 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 IRST ahead or behind GMT?

IRST is ahead of GMT by 2 hours and 30 minutes. Clocks in IRST show a later time than GMT, meaning the day starts earlier in IRST relative to GMT. For example, when it's morning in GMT, it's later in the morning in IRST. This gap may change by one hour during DST transitions.

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 GMT to IRST conversions.

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.

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

The best time for a call between GMT and IRST is during overlapping business hours (9 AM – 5 PM) in both timezones. To reach someone in IRST during their work day, call between 6:30 AM and 2:30 PM your GMT time. Avoid calling too early or late, as the 2 hours and 30 minutes difference means your evening could be their late night. 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 GMT and IRST 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 GMT and IRST ever have the same time?

No, GMT and IRST 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.

GMT to IRST Converter

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

Timezone Details

Greenwich Mean Time

3:31 AM

Friday, April 3, 2026

BST (UTC+01:00)

Tehran

6:01 AM

Friday, April 3, 2026

Tehran (UTC+03:30)

Difference: +2h 30m

BST DST: Yes (BST)

24-Hour Overview

BST — 24-hour overview

12a12a

3a3a

6a6a

9a9a

10a

11a

12p12p

3p3p

6p6p

9p9p

10p

11p

NightMorningBusinessEvening

Tehran — 24-hour overview

2a2a

5a5a

8a8a

10a

11a11a

12p

2p2p

5p5p

8p8p

10p

11p11p

12a

NightMorningBusinessEvening

Frequently Asked Questions

Related Conversions

IRST to GMT 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

GMT Cities

London Manchester Edinburgh

IRST Cities

Tehran

More Tools

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

Learn More

How Time Zones Work Understanding DST Timezone Abbreviations

External Resources

Greenwich Mean Time on Wikipedia IANA Time Zone Database