Conversion Updated: July 19, 2026

Time Conversion Calculator

IST to GMT Converter

Convert India Standard Time to GMT with date-aware logic, a 24-hour table, meeting planner, and copy-ready result.

Typical differenceGMT is 5:30 behindFixed-offset conversion for the selected date.

Convert IST to GMT

Choose a date and time in India Standard Time. The calculator will show the matching GMT time.

Conversion basis
Date-aware India Standard TimeUses Asia/Kolkata rules for the selected date.
GMT resultThe target offset is calculated from the exact converted instant.
Choose a date and time to convert.
Converted GMT time--GMT
Time difference--Compared with India Standard Time
IST offset----
GMT offset----
Copy-ready inviteConvert a time to build an invite snippet.

Suggested meeting times

Suggested meeting windowPick a suggested time or drag the bar.The third timeline row follows your auto-detected or searched timezone.

Timeline visualizer

Drag any row to move the meeting time. Green marks business hours, yellow marks daylight edges, and dark blue marks night.

Selected time--
Business hours Daylight edge Night Current time

24-hour IST to GMT conversion table

Full-day conversion for the selected date.

India Standard TimeGMTMeeting note
Select a time and convert to generate the table.
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IST to GMT: quick answer

To convert Indian Standard Time (IST) to Greenwich Mean Time (GMT), subtract 5 hours and 30 minutes. For example, 8:00 PM IST is 2:30 PM GMT on the same date. IST is fixed at UTC+5:30 and GMT is fixed at UTC+0, so this difference does not change during the year.

Important: GMT is not automatically the same as current London time. The United Kingdom uses GMT in winter and British Summer Time (BST, UTC+1) in summer. If you need the time currently observed in London, use the date-aware IST to London converter when that page becomes available.

How to convert IST to GMT

Use this fixed-offset formula:

GMT = IST − 5 hours 30 minutes

  1. Start with the date and time in IST.
  2. Subtract five hours.
  3. Subtract another 30 minutes.
  4. If the result passes midnight, move to the previous calendar date.

Example: 10:15 AM IST − 5 hours 30 minutes = 4:45 AM GMT. The calculator performs the conversion from the exact instant and shows the corresponding date automatically.

Common IST to GMT conversions

ISTGMTDate note
6:00 AM12:30 AMSame date
9:00 AM3:30 AMSame date
12:00 PM6:30 AMSame date
3:00 PM9:30 AMSame date
6:00 PM12:30 PMSame date
8:00 PM2:30 PMSame date
10:00 PM4:30 PMSame date
12:00 AM6:30 PMPrevious date

GMT versus London time

GMT is a fixed UTC+0 time standard. London uses GMT during the United Kingdom’s winter period, but it moves to British Summer Time (UTC+1) during the summer period. Therefore, an IST-to-GMT result is always 5 hours 30 minutes behind IST, while an IST-to-London result can be either 5 hours 30 minutes or 4 hours 30 minutes behind IST depending on the date.

TargetOffsetDifference from ISTSeasonal?
GMTUTC+05 hours 30 minutes behindNo
London on GMTUTC+05 hours 30 minutes behindUK winter
London on BSTUTC+14 hours 30 minutes behindUK summer

When the calendar date changes

IST times from 12:00 AM through 5:29 AM convert to the previous calendar date in GMT. For example, 2:00 AM IST on July 20 equals 8:30 PM GMT on July 19. At exactly 5:30 AM IST, the GMT result is 12:00 AM on the same date.

Best IST to GMT meeting times

For teams using fixed GMT, a practical overlap is usually 2:30 PM–6:30 PM IST, which corresponds to 9:00 AM–1:00 PM GMT. If the other participant is actually in London, verify whether the selected date uses GMT or BST before sending the invitation.

Formula, precision and verification

This converter treats IST as UTC+05:30 and GMT as UTC+00:00. It converts the entered IST date and time to an exact instant, applies the fixed GMT offset, and then calculates the target calendar date. No daylight-saving adjustment is applied to GMT.

  • Formula tested: GMT = IST − 05:30.
  • Boundary tests: midnight, 5:29 AM, 5:30 AM, noon and 11:59 PM IST.
  • Date tests: previous-date rollovers and month/year boundaries.
  • Cross-check: results compared with UTC arithmetic and the configured UTC offsets.
  • Last reviewed: July 19, 2026 by the CalculatorGeek Algorithmic Team.

Frequently asked questions

What is the time difference between IST and GMT?

GMT is exactly 5 hours and 30 minutes behind IST. The difference is fixed because neither IST nor GMT changes its UTC offset.

What is 8 PM IST in GMT?

8:00 PM IST is 2:30 PM GMT on the same calendar date.

What is 9 PM IST in GMT?

9:00 PM IST is 3:30 PM GMT on the same date.

Is GMT the same as London time?

Only during the part of the year when the UK observes GMT. London observes BST (UTC+1) during the summer period, so use a date-aware London converter for current UK civil time.

Does the IST to GMT difference change during the year?

No. IST is UTC+5:30 and GMT is UTC+0 throughout the year. Seasonal changes apply to locations such as London, not to GMT itself.

How do I convert IST to GMT manually?

Subtract 5 hours and 30 minutes from the IST time. If the result crosses midnight, use the previous date.

Related converters and references

Authoritative references: IANA Time Zone Database, BIPM time metrology, CSIR–National Physical Laboratory India, and UK clock-change guidance.