Puerto Rico time zone history
Puerto Rico has kept UTC−4 since 1899, with no clock changes since 1970, the longest run of the 16 zones on UTC−4 standard time with no change of standard time since 1970. The zone’s clock record is used in 20 countries and territories today.
UTC−4
Standard time is UTC−4 (AST) all year under the current rules.
UTC−4 every day since 1970
Before 1970
Standard time changes
| Date | Change | New standard time | Clock label |
|---|---|---|---|
| Before 1970 | |||
| March 28, 1899 | Local mean time (UTC−4:24:25) replaced | UTC−4 | AST |
Daylight saving periods
| Years | Clocks go forward | Clocks go back | Shift and labels |
|---|---|---|---|
| 1942 | May 3 | not that year | 1 hour, AST to AWT |
| 1945 | not that year | September 30 | 1 hour |
Also on UTC−4
Dominican Republic, Martinique, Venezuela, Barbados, Bermuda, Guyana, Boa Vista (Brazil), Manaus (Brazil), Halifax (Canada) and Porto Velho (Brazil) (nearest first; 8 more on the list of offsets).
Clocks next door since 1970
- Dominican Republic (400 km): same time except 1,795 days in 1970–1974 and 2000.
- Turks and Caicos Islands (622 km): same time except 10,062 days in 1970–2015 and 2018–2026; 1 hour behind today.
- Haiti (657 km): usually 1 hour behind; different on 6,726 days in 1983–1997, 2005, 2006, 2012–2015 and 2017–2026.
- Martinique (687 km): same time except 175 days in 1980.
- Venezuela (890 km): same time except 3,066 days in 2007–2016.
How it compares
On standard time, clocks in Puerto Rico run 24 minutes ahead of local mean solar time.