How to convert time zones: worked examples

Subtract the starting offset, then add the destination offset

To convert a local time, first find each location’s UTC offset for the date of the event. Subtract the starting location’s offset to get UTC, then add the destination’s offset. Equivalently, add the difference between the destination offset and the starting offset to the original clock reading.

For example, if the starting offset is UTC+1 and the destination is UTC+5:30, the destination is four hours and thirty minutes ahead. A 09:00 start becomes 13:30. Keep the minutes in the calculation: rounding either offset to a whole hour produces the wrong answer.

Worked examples for 15 January 2026

These examples use each city’s offset on 15 January 2026. They describe a specific date, not a permanent difference. The last row also changes the destination’s calendar date.

Check the London–Mumbai example in the converter →

Use the event date, not today’s offset

A city’s offset may differ between winter and summer. On 15 July 2026, London is UTC+1, so 09:00 in London corresponds to 13:30 in Mumbai. Copying the January answer would put the July appointment an hour late.

A fixed reference such as UTC−5 never changes. A city zone such as America/New_York contains rules that can change the offset with the date. Use the city when an invitation means the local time people will see there, and a fixed offset when the invitation explicitly specifies it.

Check the calendar date and any repeated hour

If addition takes you past 23:59, carry the result into the next date. If subtraction takes you before 00:00, use the previous date. The weekday may change too, so a Friday evening event can land on Saturday morning elsewhere.

Around a clock change, the starting local time can be skipped or occur twice. In that case, a clock reading and city alone are insufficient. Choose a valid local time or identify which occurrence you mean before sharing the converted result.

Understand skipped and repeated local times →