Time zone · Americas
HDT
Hawaii-Aleutian Daylight Time
Hawaii-Aleutian Daylight Time (HDT) is UTC-09:00, the summer time used on Adak and the western Aleutian Islands of Alaska. Clocks move forward one hour from Hawaii-Aleutian Standard Time (UTC-10:00) on the second Sunday in March and back on the first Sunday in November. Hawaii does not use it.
Wednesday, October 14, 2026
Current offset
UTC-09:00
Daylight · HDT
Daylight saving
Active
Reverts 1 Nov 2026
IANA zones
1
1 observe DST, 0 don't
DST offset
—
No summer variant
About HDT
Standard time, with a summer shift.
Hawaii-Aleutian Daylight Time (HDT) is UTC-09:00, the summer time used on Adak and the western Aleutian Islands of Alaska. Clocks move forward one hour from Hawaii-Aleutian Standard Time (UTC-10:00) on the second Sunday in March and back on the first Sunday in November. Hawaii does not use it.
IANA zones · the technical identifiers
The zone that resolve to HDT.
For software, always store the IANA identifier — never the abbreviation alone. The database keeps these zones distinct because their rules can, and historically did, diverge.
Where HDT is used
One country.
Same offset · UTC-09:00
Other zones at UTC-09:00 right now.
These named zones share HDT's offset today. When daylight saving rules differ, they drift apart for part of the year.
Convert
HDT to the world's clocks.
Frequently asked questions
Common questions about HDT, daylight saving, and how to handle it in software. Can't find what you need? Email [email protected].
- When does Hawaii-Aleutian Daylight Time start and end?
- It typically begins on the second Sunday in March and ends in early November, so most of the warmer months fall under the HDT offset.
- Why does this region observe daylight saving time?
- Adak is part of Alaska, and like most of the United States it follows the federal daylight saving schedule, moving clocks forward in March and back in November.
- Is Adak the only major place keeping HDT?
- Yes. HDT is used only on Adak and the rest of the Aleutian Islands west of 169.5°W. Hawaii stays on standard time all year.
- How does HDT affect neighbors like Hawaii?
- Hawaii stays on UTC-10:00 all year, so while Adak is on HDT (March to November) it is one hour ahead of Honolulu. The rest of the year they share the same time.
- How rare is the HDT label?
- Very rare. Only Adak and the western Aleutian Islands use it.
- Does HDT’s agenda align with other global daylight shifts?
- It follows the US schedule (second Sunday in March to first Sunday in November), which most of Canada also uses. Europe changes clocks on the last Sundays of March and October.
Source: IANA tzdb2026d · Reviewed
Free · Developer API
This time zone, as JSON.
Its defining offset, DST status and member counts, from one endpoint.
Also in the API: time zones by coordinates, conversions that flag daylight saving gaps, and abbreviations decoded.
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