Uruguay time zone history
Its seasonal clock changes since 1970 include moves of 30 minutes, not the usual hour. The record holds 7 different UTC offsets, tied third-most among all 312 zones. Daylight saving time was used in 28 years since 1970, last in 2015; under the current rules the clocks no longer change.
UTC−3
Standard time is UTC−3 all year under the current rules.
Summer time in 28 of 57 years since 1970
Before 1970
Standard time changes
| Date | Change | New standard time | Clock label |
|---|---|---|---|
| Before 1970 | |||
| June 10, 1908 | Local mean time (UTC−3:44:51) replaced | UTC−3:44:51 | MMT |
| May 1, 1920 | Standard time back 15 minutes | UTC−4 | numeric only |
| October 1, 1923 | Standard time forward 30 minutes | UTC−3:30 | numeric only |
| December 14, 1942 | Standard time forward 30 minutes | UTC−3 | numeric only |
Daylight saving periods
| Years | Clocks go forward | Clocks go back | Shift and labels |
|---|---|---|---|
| Before 1970 | |||
| 1924–1925 | 1 October, 00:00 | 1 April, 00:00 | 30 minutes |
| 1926 | not that year | April 1 | 30 minutes |
| 1933 | October 29 | not that year | 30 minutes |
| 1934 | October 28 | April 1 | 30 minutes |
| 1935–1938 | last Sunday in October, 00:00 | last Sunday in March, 00:00 | 30 minutes |
| 1939 | October 1 | March 26 | 30 minutes |
| 1940 | October 27 | March 31 | 30 minutes |
| 1941 | August 1 | March 30 | 30 minutes |
| 1943 | not that year | March 14 | 30 minutes |
| 1959 | May 24 | November 15 | 30 minutes |
| 1960 | January 17 | March 6 | 1 hour |
| 1965 | April 4 | September 26 | 1 hour |
| 1968 | May 27 | December 1 | 30 minutes |
| Since 1970 | |||
| 1970 | April 25 | June 14 | 1 hour |
| 1972 | April 23 | July 16 | 1 hour |
| 1974 | January 13, December 22 | March 10, September 1 | 1 hour 30 minutes |
| 1975 | not that year | March 30 | 1 hour 30 minutes |
| 1976 | December 19 | not that year | 1 hour 30 minutes |
| 1977 | December 4 | March 6 | 1 hour |
| 1978 | December 17 | March 5 | 1 hour |
| 1979 | April 29 | March 4 | 1 hour |
| 1980 | not that year | March 16 | 1 hour |
| 1987 | December 14 | not that year | 1 hour |
| 1988 | December 11 | February 28 | 1 hour |
| 1989 | October 29 | March 5 | 1 hour |
| 1990 | October 21 | February 25 | 1 hour |
| 1991 | October 27 | March 3 | 1 hour |
| 1992 | October 18 | March 1 | 1 hour |
| 1993 | not that year | February 28 | 1 hour |
| 2004 | September 19 | not that year | 1 hour |
| 2005 | October 9 | March 27 | 1 hour |
| 2006–2014 | first Sunday in October, 02:00 | second Sunday in March, 02:00 | 1 hour |
| 2015 | not that year | March 8 | 1 hour |
Also on UTC−3
Buenos Aires (Argentina), Cordoba (Argentina), San Luis (Argentina), Paraguay, Catamarca (Argentina), La Rioja (Argentina), Mendoza (Argentina), San Juan (Argentina), Tucumán (Argentina) and Salta (Argentina) (nearest first; 19 more on the list of offsets).
Clocks next door since 1970
- Buenos Aires (Argentina) (207 km): same time except 2,711 days in 1970, 1972, 1974–1980, 1987–1991, 1993 and 2004–2015.
- Cordoba (Argentina) (838 km): same time except 2,942 days in 1970, 1972, 1974–1980, 1987–1991, 1993 and 2004–2015.
- San Luis (Argentina) (949 km): same time except 4,053 days in 1970, 1972, 1974–1980, 1987–1993 and 2004–2015.
- Paraguay (1,081 km): usually 1 hour behind; different on 7,562 days in 1970 and 1972–2026; same time today.
- Catamarca (Argentina) (1,154 km): same time except 3,094 days in 1970, 1972, 1974–1980, 1987–1991, 1993 and 2004–2015.
- Santiago (Chile) (1,338 km): usually 1 hour behind; different on 7,981 days in 1970–2026.
How it compares
In 1974 the clocks were changed 4 times.
Clocks were first moved for daylight saving in 1923, the earliest start of the 37 zones in South America that ever used daylight saving time.
Standard time has stayed at UTC−3 since 1942.
On standard time, clocks in Montevideo run 45 minutes ahead of local mean solar time.