Pacific/Guam time zone
11:53PMChST
ChSTUTC+10+15 h vs New York (you)
No transitions: Pacific/Guam stays on ChST (UTC+10).
About Pacific/Guam
Pacific/Guam is the IANA time zone for Guam and Northern Mariana Islands. It currently keeps Chamorro Standard Time (ChST, UTC+10) all year.
The zone serves 2 countries or territories because their clocks have agreed since 1970; tzdata lists them together in zone1970.tab. That says nothing about borders or sovereignty, as the file’s header points out.
Its principal location is Guam at 13.47° N, 144.75° E.
Abbreviations in use: ChST. Offset page: UTC+10.
Rule for future years (POSIX TZ string)
ChST-10
The standard time is called ChST and is UTC+10. POSIX writes the offset with the opposite sign (west of Greenwich is positive), which is why the string says "-10". There is no daylight saving rule: the zone stays on this offset for every year after the end of its explicit transitions. Software that has no full tzdata copy, such as many embedded devices, can use this string directly as the TZ environment variable.
History of Pacific/Guam since 1970
The record starts with local mean time (UTC−14:21), which ended on December 31, 1844. The first daylight saving time in the record is in 1959.
| Years | Clocks | Abbreviations |
|---|---|---|
| 1970–1971 | UTC+10 in winter, UTC+11 in summer | GST, GDT |
| 1972 | UTC+10 all year | GST |
| 1973 | UTC+10 until December 16, then UTC+11 | GST, GDT |
| 1974 | UTC+11 until February 24, then UTC+10 | GDT, GST |
| 1975 | UTC+10 all year | GST |
| 1976–1977 | UTC+10 in winter, UTC+11 in summer | GST, GDT |
| 1978 onward | UTC+10 all year | GST, ChST |
Before 1970
10 offset changes before 1970 in the record:
- Tuesday, December 31, 1844: UTC−14:21 → UTC+9:39
- Tuesday, January 1, 1901: UTC+9:39 → UTC+10 (GST)
- Wednesday, December 10, 1941: UTC+10 → UTC+9
- Monday, July 31, 1944: UTC+9 → UTC+10 (GST)
- Saturday, June 27, 1959: UTC+10 → UTC+11 (GDT), daylight saving time
- Sunday, January 29, 1961: UTC+11 → UTC+10 (GST)
- Friday, September 1, 1967: UTC+10 → UTC+11 (GDT), daylight saving time
- Sunday, January 26, 1969: UTC+11 → UTC+10 (GST)
- Sunday, June 22, 1969: UTC+10 → UTC+11 (GDT), daylight saving time
- Sunday, August 31, 1969: UTC+11 → UTC+10 (GST)
Changes of the winter (standard) offset: Sunday, August 31, 1969, UTC+11 → UTC+10.
tzdata commits to accuracy from 1970 for every zone (zone1970.tab); earlier entries are historical research and may be incomplete.
Aliases and zones with the same clock
These older or country-specific IDs are links to Pacific/Guam in tzdata. Their pages redirect here: Pacific/Saipan.
Other zones that keep exactly the same time under the current rules (but have a different history): Asia/Ust-Nera, Asia/Vladivostok, Australia/Brisbane, Australia/Lindeman, Pacific/Port_Moresby.
Places on Pacific/Guam
Convert Guam time
Using Pacific/Guam in code
Every major platform reads the same IANA ID. Store instants in UTC and convert with the ID at display time; never store a fixed offset for a place that has daylight saving time.
// JavaScript
new Date().toLocaleString('en-US', { timeZone: 'Pacific/Guam' })
# Python 3.9+
from zoneinfo import ZoneInfo
from datetime import datetime
datetime.now(ZoneInfo('Pacific/Guam'))
// Java
java.time.ZonedDateTime.now(java.time.ZoneId.of("Pacific/Guam"))
// Go
loc, _ := time.LoadLocation("Pacific/Guam")
time.Now().In(loc)
-- PostgreSQL
SELECT now() AT TIME ZONE 'Pacific/Guam';
# Shell
TZ='Pacific/Guam' datePlatforms ship their own copy of tzdata and update it on their own schedule. After a rule change, outputs can differ until the platform updates; this page uses tzdata 2026f.