EST vs EDT: US time zone abbreviations
EST (Eastern Standard Time) is UTC−5 and applies from early November to mid-March. EDT (Eastern Daylight Time) is UTC−4 and applies the rest of the year. Every US zone that observes daylight saving has the same pair: CST/CDT, MST/MDT, PST/PDT and AKST/AKDT. When you don’t want to think about the season, write ET, CT, MT or PT: they always mean “whatever the local clock says”.
Every US zone, right now
| Zone | Winter (standard) | Summer (daylight) | In use now | Next switch |
|---|---|---|---|---|
| Eastern Time | EST (UTC-5) | EDT (UTC-4) | EDT UTC-4 | Nov 1, 2026 |
| Central Time | CST (UTC-6) | CDT (UTC-5) | CDT UTC-5 | Nov 1, 2026 |
| Mountain Time | MST (UTC-7) | MDT (UTC-6) | MDT UTC-6 | Nov 1, 2026 |
| Pacific Time | PST (UTC-8) | PDT (UTC-7) | PDT UTC-7 | Nov 1, 2026 |
| Alaska Time | AKST (UTC-9) | AKDT (UTC-8) | AKDT UTC-8 | Nov 1, 2026 |
| Hawaii–Aleutian Time | HST (UTC-10) | — | HST UTC-10 | No DST |
| Arizona (most of the state) | MST (UTC-7) | — | MST UTC-7 | No DST |
The “In use now” and “Next switch” columns are recomputed from your device’s time zone database when the page loads.
When each abbreviation applies
Since 2007, US daylight saving time starts at 2:00 AM local time on the second Sunday in March and ends at 2:00 AM on the first Sunday in November (15 U.S.C. § 260a, as amended by the Energy Policy Act of 2005). Between those dates the daylight abbreviation (EDT, CDT, MDT, PDT, AKDT) is correct; the rest of the year the standard one (EST, CST, MST, PST, AKST). The daylight saving map shows which places switch.
Two places never switch. Hawaii keeps HST (UTC−10) all year, and most of Arizona keeps MST (UTC−7). The Navajo Nation in northeastern Arizona does observe daylight time, so it uses MDT in summer while Phoenix stays on MST. Alaska’s western Aleutian Islands use HST/HDT (UTC−10/−9), one of the few places that use the Hawaii–Aleutian zone with daylight saving.
Common mistakes
- “3 PM EST” in July. Strictly, that is 4 PM on New York clocks, because EST is UTC−5 and New York is on UTC−4. Most readers will assume you meant Eastern time, but software that parses “EST” literally will be an hour off. Write “3 PM ET”.
- Assuming Arizona is on Pacific time. It isn’t; it’s Mountain Standard Time all year, which happens to match Pacific Daylight Time from March to November.
- Using the abbreviation as a unique id. “CST” also means China Standard Time and Cuba Standard Time. Software should store IANA ids such as
America/Chicago, which also carry the DST rules. - Hardcoding offsets. An offset like UTC−5 describes a moment, not a place. New York is UTC−5 in January and UTC−4 in July.
Converting between them
Abbreviations within the same season are whole hours apart: ET is one hour ahead of CT, two of MT and three of PT, all year. To convert a specific time, use thetime zone converter; it picks the right offset for today. For common pairs there are dedicated pages, such as EST to PST and CST to EST.
Key takeaways
- EST = UTC−5 (winter), EDT = UTC−4 (summer); the other zones follow the same pattern.
- Write ET/CT/MT/PT in invites; store IANA ids in software.
- Arizona (except the Navajo Nation) and Hawaii never switch.
Sources
- 15 U.S.C. §§ 260–267 (Uniform Time Act), including § 260a on daylight saving dates.
- Abbreviations and offsets: the IANA time zone database, read live by your browser.