IST to GMT

The difference month by month, the two long stretches it takes across the year, and what that means for a call between Mumbai and London.

How far apart are IST and GMT?

GMT is 4 hours, 30 minutes behind IST for most of the year.

When it is 9:00 AM in Mumbai, it is 4:30 AM in London.

Right now

The current reading appears once this page finishes loading.

How does the difference change month by month?

Any answer that quotes one number for this pair is wrong for part of the year. Here is the difference in force in each month of 2026, with the exact day it changes.

Show the month-by-month table

Difference between IST and GMT by month, 2026
Month	Difference	Changes on	New difference
January	−5:30	No change
February	−5:30	No change
March	−5:30	March 29, 2026	−4:30
April	−4:30	No change
May	−4:30	No change
June	−4:30	No change
July	−4:30	No change
August	−4:30	No change
September	−4:30	No change
October	−4:30	October 25, 2026	−5:30
November	−5:30	No change
December	−5:30	No change

Dates here are calendar dates in IST time. Where a clock change happens overnight, the calendar in the other zone can already have turned over.

When does the usual difference not hold?

It holds for one long stretch at a time. Only one of these two zones moves its clocks, so the difference takes two values across the year rather than breaking for a few weeks. These are the exact stretches.

Show every dated difference period

Every period of constant difference, 2026 to 2027
From	Until	Difference	Days
Thu, January 1, 2026	Sat, March 28, 2026	−5:30	87
Sun, March 29, 2026	Sat, October 24, 2026	−4:30	210
Sun, October 25, 2026	Sat, March 27, 2027	−5:30	154
Sun, March 28, 2027	Sat, October 30, 2027	−4:30	217
Sun, October 31, 2027	Fri, December 31, 2027	−5:30	62

Every offset on this page comes from IANA tzdata 2026c, released July 8, 2026. The pinned table covers 2024–2032. How these times are derived