Guam time zone history
The record holds 5 different UTC offsets, the second-most of the 10 zones on UTC+10 standard time. Daylight saving time was used in 6 years since 1970, last in 1977; under the current rules the clocks no longer change.
UTC+10
Standard time is UTC+10 (ChST) all year under the current rules.
Summer time in 6 of 57 years since 1970
Before 1970
Standard time changes
| Date | Change | New standard time | Clock label |
|---|---|---|---|
| Before 1970 | |||
| December 31, 1844 | Standard time forward 24 hours | UTC+9:39 | LMT |
| January 1, 1901 | Local mean time (UTC+9:39) replaced | UTC+10 | GST |
| December 10, 1941 | Standard time back 1 hour | UTC+9 | numeric only |
| July 31, 1944 | Standard time forward 1 hour | UTC+10 | GST |
Daylight saving periods
| Years | Clocks go forward | Clocks go back | Shift and labels |
|---|---|---|---|
| Before 1970 | |||
| 1959 | June 27 | not that year | 1 hour, GST to GDT |
| 1961 | not that year | January 29 | 1 hour |
| 1967 | September 1 | not that year | 1 hour, GST to GDT |
| 1969 | June 22 | January 26, August 31 | 1 hour, GST to GDT |
| Since 1970 | |||
| 1970–1971 | last Sunday in April, 02:00 | first Sunday in September, 02:00 | 1 hour, GST to GDT |
| 1973 | December 16 | not that year | 1 hour, GST to GDT |
| 1974 | not that year | February 24 | 1 hour, GST to GDT |
| 1976 | May 26 | August 22 | 1 hour, GST to GDT |
| 1977 | April 24 | August 28 | 1 hour, GST to GDT |
Also on UTC+10
Port Moresby (Papua New Guinea), Vladivostok (Russia), Lindeman (Australia), Brisbane (Australia), Sydney (Australia), Ust-Nera (Russia), Melbourne (Australia), Hobart (Australia) and Macquarie Island (Australia).
Clocks next door since 1970
- Palau (1,313 km): usually 1 hour behind; different on 550 days in 1970, 1971, 1973, 1974, 1976 and 1977.
- Jayapura (Indonesia) (1,834 km): usually 1 hour behind; different on 550 days in 1970, 1971, 1973, 1974, 1976 and 1977.
- Micronesia (2,194 km): usually 1 hour ahead; different on 10,042 days in 1970–1998.
- Bougainville (Papua New Guinea) (2,493 km): same time except 4,937 days in 19 different years between 1970 and 2026; 1 hour ahead today.
- Marshall Islands (2,509 km): usually 2 hours ahead; different on 8,634 days in 1970–1993.
How it compares
Guam kept local mean time (UTC+9:39) until 1901, the third-latest switch of the 9 zones on UTC+10 standard time with local mean time in the record.
Standard time has stayed at UTC+10 since 1944.
On standard time, clocks in Guam run 21 minutes ahead of local mean solar time.