IST to GMT Converter

The UK is not on GMT all year

Greenwich Mean Time is UTC+0, and the UK uses it from late October to late March. For the rest of the year the UK is on British Summer Time at UTC+1. Since India stays at UTC+5:30 throughout, the gap between Bengaluru and London is 5.5 hours in the UK winter and 4.5 hours in the UK summer.

The changeovers are the last Sunday in March and the last Sunday in October, at 1:00 AM UTC. They do not coincide with the US changes, which is why there is a short window each spring and autumn when the usual relationship between London and New York is temporarily different from the rest of the year.

Writing "GMT" when you mean "UK time" in July is a common source of confusion, because at that point the two differ by an hour. This converter resolves it by working from London as a place rather than from the acronym.

The most workable overlap of any India pairing

India and the UK have the largest genuine overlap of the common offshore pairings. With nine-to-six days at both ends, the shared window runs from roughly 9:00 AM UK time to about 12:30 PM UK time in winter, and an hour longer in summer terms, which is the early afternoon in India.

That means an India-UK team can hold a normal mid-morning call without anybody working outside their hours, which is not true of India and either US coast. If your team spans India, the UK and the US East Coast, the binding constraint will be the US leg, not the UK one.

• 9:00 AM in London is 2:30 PM in Bengaluru during GMT, 1:30 PM during BST.
• 2:00 PM in Bengaluru is 8:30 AM in London during GMT, 9:30 AM during BST.
• A late-morning UK call sits comfortably in the Indian afternoon all year.

The weeks when a recurring call moves

On the last Sunday in March the UK moves forward an hour, so a Monday call that was at 2:30 PM India time is suddenly at 1:30 PM India time if it stays pinned to UK local time. The reverse happens at the end of October. Teams that schedule in UK local time see the Indian side shift; teams that schedule in Indian local time see the UK side shift.

Neither option avoids the change, so the practical advice is to decide which side you would rather protect and be explicit about it. Checking a date either side of the transition in the converter before the week arrives takes a few seconds and prevents the usual round of confused messages on the Monday.