GMT to IST
London to Mumbai.
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All date & timeQuestions
What time is IST when it is 12:00 GMT?
17:30. India Standard Time is 5 hours 30 minutes ahead of Greenwich Mean Time in January and 4 hours 30 minutes ahead of it in July. The gap moves because London observes daylight saving and Mumbai does not, so the difference between them is not a fixed number. A 9-to-5 day in London overlaps a 9-to-5 day in Mumbai for 2.5 hours, between 09:00 and 11:30 GMT.
Is the difference between GMT and IST the same all year?
No, and this is the pair where that matters. India Standard Time is 5 hours 30 minutes ahead of Greenwich Mean Time in January and 4 hours 30 minutes ahead of it in July. The gap moves because London observes daylight saving and Mumbai does not, so the difference between them is not a fixed number. Booking a recurring call across these two and assuming one number will drift by an hour twice a year — check the date, not just the zones.
What do GMT and IST actually stand for?
GMT is Greenwich Mean Time, the zone covering London, currently UTC+0 in January. IST is India Standard Time, covering Mumbai, at UTC+5:30. GMT and UK time are the same thing only in winter. From late March to late October London runs on British Summer Time, an hour ahead of GMT, so a meeting booked as 'GMT' with someone in London is an hour out for most of the year.
Anything worth knowing about India Standard Time?
One of a handful of zones offset by half an hour rather than a whole one — UTC+5:30 for the entire country, from Gujarat to Arunachal Pradesh. India has no daylight saving, so the offset is the same all year.
When is a good time to call between London and Mumbai?
A 9-to-5 day in London overlaps a 9-to-5 day in Mumbai for 2.5 hours, between 09:00 and 11:30 GMT. If the call has to happen outside that, the fairer arrangement is usually to alternate which side takes the awkward hour rather than always asking the same one.
How it works, and more about gmt → ist
The difference, and whether you can rely on it
In January, India Standard Time is 5 hours 30 minutes ahead of Greenwich Mean Time — UTC+0 against UTC+5:30. In July it is 4 hours 30 minutes ahead instead. That is the part worth carrying away: this is not a pair you can memorise a single number for.
Why the gap moves
London observes daylight saving; Mumbai does not. So the clocks in one city move twice a year while the other stays put, and the distance between them changes with them. Any calculation you did in one season is wrong in the other. The converter above uses the date you give it rather than today’s offset, which is the only way to get a future meeting right when it falls on the other side of a changeover.
When you can both be at a desk
A standard working day in London overlaps one in Mumbai between 09:00 and 11:30 GMT — 3 hours. Anything outside that asks somebody to start early or finish late.
Reading the abbreviations literally will mislead you
GMT strictly means one fixed offset, but almost nobody uses it that way. People write it to mean the time in London, which shifts if that city observes daylight saving — and it does. This page follows the common usage rather than the strict one, because the strict reading gives an answer that is wrong for a good part of the year.
GMT and UK time are the same thing only in winter. From late March to late October London runs on British Summer Time, an hour ahead of GMT, so a meeting booked as 'GMT' with someone in London is an hour out for most of the year. One of a handful of zones offset by half an hour rather than a whole one — UTC+5:30 for the entire country, from Gujarat to Arunachal Pradesh. India has no daylight saving, so the offset is the same all year.
Scheduling something recurring
For a one-off, the converter above is the whole job. For a standing meeting across these two zones, where the gap changes, it is worth putting the invitation in a calendar that stores the zone rather than the time — then the changeover is handled for you and nobody has to remember. If you are trying to find a slot across more than two places at once, the meeting planner shows a whole day at a glance instead.