Mumbai is 4 hours 30 minutes ahead of London. Put the other way round: London is 4 hours 30 minutes behind Mumbai.
London is UTC+1 in summer and UTC in winter; Mumbai is UTC+5:30 and UTC+5:30.
Working 09:00 to 17:00 in both cities leaves 3.5 hours in common: 09:00 to 12:30 in London, which is 13:30 to 17:00 in Mumbai. Those are the hours to aim a call at.
London changes its clocks for summer and Mumbai does not, so there is no single answer: the gap is 4 hours 30 minutes for the northern summer and 5 hours 30 minutes for the rest of the year.
| London | Mumbai |
|---|---|
| 08:00 | 12:30 |
| 09:00 | 13:30 |
| 10:00 | 14:30 |
| 11:00 | 15:30 |
| 12:00 | 16:30 |
| 13:00 | 17:30 |
| 14:00 | 18:30 |
| 15:00 | 19:30 |
| 16:00 | 20:30 |
| 17:00 | 21:30 |
| 18:00 | 22:30 |
This page covers one pair. TimeGap takes a list: add every city you care about, drag one marker, and every row reads the same instant on its own clock. It marks the hours you would actually take a call, finds the window where the most people are reachable, flags public holidays, and puts the time you pick straight into Outlook or Google Calendar.