What is the difference between EST and EDT?
The difference between EST and EDT is one hour, and which one is correct depends on the time of year. Eastern Standard Time (EST) and Eastern Daylight Time (EDT) are not two separate zones — they are the winter and summer settings of a single zone, United States Eastern Time. In winter the zone keeps standard time and sits five hours behind Coordinated Universal Time, written UTC−5; in summer daylight saving time advances every clock in the zone by one hour, to UTC−4, and the abbreviation changes from EST to EDT.1
The U.S. Naval Observatory states the two offsets directly: to convert from Coordinated Universal Time you subtract five hours for Eastern Standard Time and four hours for Eastern Daylight Time.1 The underlying time zone is the same throughout — the time-zone database that software uses to compute local time records the whole region as a single entry, America/New_York, whose abbreviation alternates between EST and EDT as the clocks change.4 Nothing about the sun or the Earth's rotation changes at the switch; only the number on the clock, and the abbreviation attached to it, moves by an hour.
When is it EST, and when is it EDT?
Eastern Daylight Time is in effect from the second Sunday of March to the first Sunday of November; Eastern Standard Time covers the rest of the year. United States law fixes the window precisely: clocks advance one hour "at 2 o'clock antemeridian on the second Sunday of March" and return "at 2 o'clock antemeridian on the first Sunday of November" each year.2 The popular shorthand is "spring forward, fall back" — the March transition skips the hour from 02:00 to 03:00, and the November transition repeats the hour from 02:00 back to 01:00.3
In a concrete year the dates land on specific Sundays. In 2026, Eastern Daylight Time runs from to — about 238 days, or roughly two-thirds of the year, on EDT, with the remaining stretch of winter on EST.2 That imbalance is why "summer time" covers far more than the summer: the daylight-saving window deliberately reaches into March and November.
Should you write EST or EDT?
Write EDT for any Eastern-zone time between mid-March and early November, and EST only in winter; when in doubt, write "ET" and let the umbrella label carry the season. The single most common mistake with these abbreviations is writing "EST" all year — treating it as a generic name for the Eastern zone rather than the name of its winter setting. For the roughly eight months the zone spends on daylight saving time, a time labelled "EST" is an hour off the time actually being kept.2
The same trap exists for every United States zone with a standard and a daylight time-zone abbreviation: Central splits into CST and CDT, Mountain into MST and MDT, and Pacific into PST and PDT. When a date or season is not specified, the unambiguous choice is the umbrella form — Eastern Time (ET), Central Time (CT), Mountain Time (MT), Pacific Time (PT) — which stays correct on both sides of the switch.
How can you tell which one is in effect right now?
To tell whether Eastern Time is currently on EST or EDT, check the calendar against the changeover dates: if the date falls between the second Sunday of March and the first Sunday of November, the zone is on EDT (UTC−4); otherwise it is on EST (UTC−5).2 A second check is the offset itself — a current Eastern time four hours behind Coordinated Universal Time is EDT, and one five hours behind is EST.1
For the live answer without doing the arithmetic, the time zone converter resolves Eastern Time against any other zone and applies the daylight-saving rule automatically, so it always shows the offset in force on the chosen date.
Who decides when Eastern Time switches?
The dates on which Eastern Time switches between EST and EDT are set by United States federal law and administered by the U.S. Department of Transportation, which oversees the nation's time zones and the uniform observance of daylight saving time.5 The current window — second Sunday of March to first Sunday of November — was set by a 2005 federal energy law and has been in effect since 2007, extending daylight saving time by about a month compared with the previous rule.3
A state may exempt itself from daylight saving time and stay on standard time all year, in which case its Eastern-zone clocks would read EST permanently and never switch to EDT; what a state cannot do, without an act of Congress, is adopt permanent daylight saving time.5 Across the populous Eastern zone — including New York, Washington, D.C., Atlanta, and Toronto, which share the America/New_York rules — daylight saving time is observed, so the EST-to-EDT switch happens on the federal dates every year.4
EST vs EDT at a glance
| Property | EST — Eastern Standard Time | EDT — Eastern Daylight Time |
|---|---|---|
| Offset from UTC | UTC−5 | UTC−4 |
| Season | Winter (standard time) | Summer (daylight saving time) |
| In effect | First Sunday of November → second Sunday of March | Second Sunday of March → first Sunday of November |
| Clock vs. EST | Base setting | One hour ahead |
| Umbrella name | Eastern Time (ET) | |
| Time-zone database zone | America/New_York |
|
Frequently asked questions
Is it EST or EDT in summer?
In summer it is EDT — Eastern Daylight Time, UTC−4. Eastern Daylight Time runs from the second Sunday of March to the first Sunday of November, so every Eastern-zone date in summer is EDT, not EST.2
Are EST and EDT the same time?
No. EST and EDT are one hour apart: Eastern Daylight Time (EDT) reads one hour later than Eastern Standard Time (EST) for the same instant, because daylight saving time advances the clock from UTC−5 to UTC−4.1
Is New York on EST or EDT?
New York is on Eastern Time, which means EST in winter and EDT in summer. The whole America/New_York zone — New York, Washington, D.C., Atlanta, and beyond — switches between the two on the same federal dates.4
What does "ET" mean?
"ET" stands for Eastern Time, the umbrella name for the zone regardless of season. It resolves to EDT (UTC−4) during daylight saving time and to EST (UTC−5) the rest of the year, which makes it the safe label when a date is not specified.4
Why do people write "EST" all year?
"EST" is widely but incorrectly used as a generic name for the Eastern zone. For the roughly eight months the zone spends on daylight saving time, the correct abbreviation is EDT; the generic name that stays right in both seasons is "ET".2
Footnotes
- 1. U.S. Time Zones (Astronomical Information Center FAQ) , U.S. Naval Observatory — accessed 2026-06-06.
- 2. 15 U.S. Code § 260a — Advancement of time or changeover dates , Office of the Law Revision Counsel, U.S. House of Representatives (Legal Information Institute edition) — accessed 2026-06-06.
- 3. Daylight Saving Time (DST) , National Institute of Standards and Technology, Time and Frequency Division — accessed 2026-06-06.
- 4. Time Zone Database — northamerica file (Zone America/New_York) , Internet Assigned Numbers Authority (IANA tz database) — accessed 2026-06-06.
- 5. Uniform Time , U.S. Department of Transportation — accessed 2026-06-06.