Hawaii-Aleutian Standard Time (HAST)
UTC offset: -10:00
IANA identifiers: Pacific/Honolulu (Hawaii), America/Adak (Aleutian Islands)
Abbreviations: HST or HAST (standard), HADT (Aleutian DST only)
Population covered: approximately 1.5 million in Hawaii, plus a few thousand in the western Aleutians
DST observed: No in Hawaii, Yes in the Aleutian Islands
Hawaii never changes its clocks. The islands sit at UTC-10:00 year-round, which makes them one of only two US states that ignore daylight saving time (Arizona being the other). The western Aleutian Islands share the same base offset but do observe DST, springing forward to UTC-09:00 in March. That creates the odd situation where two regions in the same nominal time zone operate differently for eight months of the year.
For most practical purposes, people mean Hawaii when they say "Hawaii time." The Aleutian Islands add maybe 8,000 residents to the zone, scattered across some of the most remote islands in the United States. The population center, the economic activity, and the cultural identity of this time zone all live in the Hawaiian archipelago.
Why Hawaii Skips Daylight Saving
Hawaii sits between 19 and 22 degrees north latitude, which is tropical. Day length doesn't vary much across the year. The longest day (about 13 hours 26 minutes in Honolulu) and the shortest day (about 10 hours 50 minutes) differ by less than three hours. Compare that to Seattle, where the difference exceeds seven hours. In Hawaii, there simply isn't enough seasonal daylight swing to make DST worthwhile.
The state did observe wartime daylight saving during World War II, from February 1942 through September 1945. After the war ended, Hawaii went back to standard time and stayed there. When the Uniform Time Act of 1966 required all states to observe DST unless they explicitly opted out, Hawaii opted out immediately. The legislature saw no benefit to disrupting schedules for a marginal change in evening light.
The result is that Hawaii's offset relative to the US mainland shifts twice a year, even though Hawaii itself doesn't move. During winter (November through mid-March), Hawaii is two hours behind the Pacific Coast, three behind Mountain, four behind Central, and five behind Eastern. During summer DST, those gaps widen by one hour each: three behind Pacific, four behind Mountain, five behind Central, six behind Eastern.
History
Before Western contact, Hawaiians tracked time by solar and lunar cycles rather than fixed hours. The modern time zone system came to the islands gradually during the 19th century as trade with the US mainland grew.
Hawaii originally used a local mean time of UTC-10:31:26, based on the longitude of Honolulu. In 1896, the Republic of Hawaii adopted a standard offset of GMT-10:30. When Hawaii became a US territory in 1900, the half-hour offset persisted until 1947, when territorial law rounded it to UTC-10:00 for simplicity and alignment with the 150th meridian west.
The Aleutian Islands were placed in the same time zone because of their longitude. Adak, the largest settlement in the western Aleutians, sits at about 176 degrees west, which is technically close to the International Date Line. Using UTC-10:00 keeps these islands on the same calendar day as the rest of the US, even though their solar time would suggest UTC-12:00 or even crossing into the next day.
Geographic Scope
Hawaii is an archipelago of 137 islands stretching about 2,400 kilometers across the central Pacific Ocean. The eight main islands (Niihau, Kauai, Oahu, Molokai, Lanai, Maui, Kahoolawe, and the Big Island of Hawaii) contain nearly all the population. Oahu alone holds about 70 percent of the state's residents.
The Aleutian Islands extend westward from the Alaska Peninsula for about 1,900 kilometers. Only the portion west of 169 degrees 30 minutes west longitude uses HAST/HADT. The rest of the Aleutian chain uses Alaska Time. The line was drawn somewhat arbitrarily, but it roughly corresponds to the natural break between the more accessible eastern Aleutians and the extremely remote western islands.
Other territories at UTC-10:00 include the Cook Islands and most of French Polynesia (Tahiti), but these are independent jurisdictions with their own time zone names.
Major Cities
Honolulu is the state capital and dominant city, with about 350,000 in the city proper and roughly 1 million in the urban Honolulu metro area on Oahu. It's the economic engine of Hawaii, anchoring tourism, military activity (Pearl Harbor and multiple US military bases), and the state government. Waikiki Beach, Diamond Head, and Pearl Harbor are global tourist landmarks.
Hilo has about 45,000 people on the Big Island's east coast. It's the gateway to Hawaii Volcanoes National Park and receives the most rainfall of any Hawaiian city, giving it a lush, tropical character distinct from the drier resort areas.
Kailua-Kona on the Big Island's west coast is the center of the Kona coffee growing region and a popular resort area. The Ironman World Championship triathlon is held here annually.
Adak in the Aleutian Islands has a population of roughly 170 people. It was a major naval station during the Cold War but has been mostly depopulated since the base closed in 1997. It remains the westernmost municipality in the United States.
Business and Tourism
Tourism is the economic backbone of Hawaii. The state receives roughly 10 million visitors per year in normal times, most arriving from the US West Coast, Japan, and Canada. The time zone position matters here: Hawaii is relatively close in clock hours to East Asia. Japan is 19 hours ahead (UTC+09:00 vs UTC-10:00), which sounds enormous but actually means that when it's morning in Honolulu, it's already the next day's morning in Tokyo. The one-day-ahead relationship makes flight scheduling somewhat intuitive for transpacific routes.
For business coordination with the US mainland, Hawaii's offset creates challenges. By the time Hawaiian offices open at 8:00 a.m., it's already 11:00 a.m. Pacific, 1:00 p.m. Central, and 2:00 p.m. Eastern during winter. In summer, add an hour to each. This means Hawaiian businesses that deal with the mainland often start early, with 6:00 or 7:00 a.m. calls being common for anyone working with East Coast partners.
The military runs on its own schedule. The US Pacific Command (USINDOPACOM), headquartered at Camp H.M. Smith on Oahu, coordinates across the entire Pacific and Indian Ocean regions. Military operations use Zulu time (UTC) internally, but the local duty day for personnel follows Hawaiian time.
Neighboring Offsets
| Zone | Offset | Difference from HAST |
|---|---|---|
| Alaska Standard Time | UTC-09:00 | 1 hour ahead |
| Pacific Standard Time | UTC-08:00 | 2 hours ahead |
| Samoa Standard Time | UTC-11:00 | 1 hour behind |
| Line Islands (Kiribati) | UTC+14:00 | Across the date line |
| New Zealand Standard Time | UTC+12:00 | 22 hours ahead (same clock, next day + 2 hrs) |
| Japan Standard Time | UTC+09:00 | 19 hours ahead |
The International Date Line lies west of Hawaii, which means Hawaii is one of the last populated places to enter each new calendar day. Only American Samoa (UTC-11:00) and a few uninhabited US minor outlying islands arrive later.
Climate and Daily Rhythm
Hawaii's tropical latitude means sunrise and sunset times barely move through the year. Sunrise ranges from about 5:50 a.m. in June to 7:10 a.m. in January. Sunset ranges from about 6:00 p.m. in December to 7:15 p.m. in July. This consistency reinforces the argument against DST. There's no dark winter morning problem to solve, and no long summer evening to extend.
The consistent schedule shapes daily life. People rise early, particularly in agriculture, fishing, and surfing culture. Lunch tends toward noon. Dinner is early by mainland standards, often 5:30 or 6:00 p.m. The pace is slower than mainland cities, something visitors notice immediately and residents defend fiercely.
Technical Identifiers
- Pacific/Honolulu (canonical for Hawaii, no DST transitions)
- America/Adak (western Aleutian Islands, observes DST)
- US/Hawaii (legacy alias for Pacific/Honolulu)
The military/aviation designation for UTC-10:00 is W ("Whiskey").
Software systems should use Pacific/Honolulu for any Hawaiian location. Using America/Adak for Hawaii will produce incorrect results during DST months.
Quick Reference
| Attribute | Value |
|---|---|
| UTC offset | -10:00 |
| DST observed | No (Hawaii), Yes (Aleutians to UTC-09:00) |
| IANA zone (Hawaii) | Pacific/Honolulu |
| IANA zone (Aleutians) | America/Adak |
| Population | ~1.5 million (Hawaii) |
| Largest city | Honolulu (~1M metro) |
| Primary industry | Tourism, military |
| Reference meridian | 150° W |
| Notable quirk | One of two US states that never observes DST |