Eastern Time to GMT: what “ET” actually means
ET is not a fixed offset. It is a promise to use whichever of two offsets is correct today — which makes it the safest thing to write and the hardest to convert blind.
The short answer
ET is 5 hours behind GMT most of the year. 09:00 ET is 14:00 in London.
But ET is not an offset — it means “EST or EDT, whichever applies on this date.” It is UTC−5 in winter and UTC−4 in summer. That is exactly why it is the correct thing to write, and why you cannot convert it without knowing the date.
ET is a promise, not a number
EST is UTC−5. EDT is UTC−4. ET is whichever one is currently in force.
That vagueness is a feature. When you write "3pm ET" you are saying "3pm in New York," and any tool resolving it against the time zone database will get the right instant on any date, including the ones near a transition. When you write "3pm EST" you are asserting a specific offset — and for eight months of the year that assertion is false.
The same applies to CT, MT and PT, and to the UK's own habit of writing "GMT" year-round when half the year it is BST.
Converting ET to London
| Period | New York | London | Gap |
|---|---|---|---|
| Nov – mid-March | EST · UTC−5 | GMT · UTC+0 | 5 hours |
| Mid-March – late March | EDT · UTC−4 | GMT · UTC+0 | 4 hours |
| Late March – late Oct | EDT · UTC−4 | GMT+1 · UTC+1 | 5 hours |
| Late Oct – early Nov | EDT · UTC−4 | GMT · UTC+0 | 4 hours |
Two rows out of four are the ordinary five hours. The other two are the gap weeks, and they are the reason a transatlantic recurring call moves.
Why the mismatch exists
The US sets its own daylight-saving dates: forward on the second Sunday in March, back on the first Sunday in November.
The UK and the EU use the last Sunday in March and the last Sunday in October.
Neither is wrong. They were simply legislated separately, and the result is roughly three weeks in spring and one in autumn when the Atlantic gap is four hours rather than five.
What it breaks in practice
- A weekly London–New York call, set in the calendar as a fixed local time on both sides, drifts by an hour for those weeks.
- Anything scheduled through the window — a deadline set in March for early April, say — is computed against the wrong offset if you did the arithmetic by hand.
- Automated reports and cron jobs that assume a constant five-hour relationship produce output an hour early or late, usually without anyone noticing until someone reconciles two logs.
The habit that avoids all of it
Write cities. "2pm London / 9am New York."
A city resolves through the IANA database, which encodes every one of these rules, including the dates they changed historically. An offset written by hand encodes only what you believed on the day you typed it.
If you need a machine-readable form, use a UTC timestamp — it has no seasonal behaviour at all. See UTC to EST.
Related: Convert EST to GMT · EST vs EDT · What is EST?
Timezone: World Clock Widget
A world clock, converter and live day/night map for iPhone — 325 cities, offline, no account.
Figures on this page are computed from the IANA time zone database. Last generated 2026-08-18.