UTC+0 · Royal Observatory, Greenwich, London · UK uses GMT in winter
GMT is always UTC+0. Other time zones shift relative to GMT — especially US zones that observe Daylight Saving Time.
| Time Zone | Offset from GMT | Difference |
|---|---|---|
| EST (New York, winter) | GMT-5 | 5 hrs behind GMT |
| EDT (New York, summer) | GMT-4 | 4 hrs behind GMT |
| CST (Chicago, winter) | GMT-6 | 6 hrs behind GMT |
| PST (Los Angeles, winter) | GMT-8 | 8 hrs behind GMT |
| BST (UK, summer) | GMT+1 | 1 hrs ahead of GMT |
| CET (Paris, winter) | GMT+1 | 1 hrs ahead of GMT |
| IST (India) | GMT+5:30 | 5:30 hrs ahead of GMT |
| JST (Tokyo) | GMT+9 | 9 hrs ahead of GMT |
GMT is 5 hours ahead of EST and 4 hours ahead of EDT. GMT itself never changes — it is always UTC+0. The difference depends on the US East Coast.
During winter (November–March), the US East Coast observes EST (UTC-5) — so GMT is 5 hours ahead.
During summer (March–November), Daylight Saving Time activates and the East Coast switches to EDT (UTC-4) — so GMT is only 4 hours ahead.
Note: The UK observes BST (British Summer Time, UTC+1) from the last Sunday in March to the last Sunday in October. During BST, the UK clock is 1 hour ahead of GMT.
These countries observe GMT (UTC+0) permanently — they do not switch to summer time:
The United Kingdom observes GMT in winter (October–March) but switches to BST (UTC+1) during Daylight Saving Time in summer.