The Ministry of Energy announced on 2015-01-28 that Chile would remain on summer time all year long, starting in 2015. On 2016-03-13, it reconsidered and reinstated the seasonal alternation. Henceforth Chile will observe standard time from the second Saturday in May to the second Saturday in August.

Rules currently in force

For March 2008 only, because of a drought, Chile extended DST to last through the last Saturday in March. For March 2010 only, because of an earthquake, Chile extended DST through April 3 at 24:00.

Geographical note:

Easter Island refers to Isla de Pascua province, which includes Isla de Pascua (Easter Island) and Isla Sala y Gómez. The other remote Pacific islands belonging to Chile, such as the Islas Juan Fernández, are in the same time zone as the mainland.

Time zone history

Source: This information was adapted from the tz database. Zone names come from that database. The names don't necessarily match any names used in the "real world".

Example: When it was 14:18 (or 2:18 p.m.) local time on 2000-09-03 (September 3, 2000) in Iquique, Chile, what was the UTC?

Iquique is on the Chilean mainland. From the first table, this is in the America/Santiago time zone. In the second table, look in the block of rows for America/Santiago. Among them, look for the first row on which the Final Date exceeds 2000-09-03 14:18. You find that the third line has a date of "Present", which is the first to exceed 2000. Looking across the row, the Chile rule applies, and standard time is UTC-4. Finally, look in the third table under the Chile rule. Once again, find the date range that includes the date in question (2000-09). That would be the last range, "1999-10 onward". This rule says that daylight saving time was in effect in Iquique until 03:00 UTC on March 12, 2000, and then standard time prevailed until 04:00 UTC on October 15, 2000. The date in question falls between those two dates, so standard time was in effect. Therefore, the local time was UTC-4. Add four hours to the given time to get UTC. The answer is 2000-09-03 18:18 UTC.

Time zone names

The tz database contains names and abbreviations for the Chilean time zones. They were created by a contributor. Don't assume that these names, or anything like them, have ever been used officially in Chile.

1. Santiago Mean Time (SMT) applies to times in the America/Santiago zone from 1890 to 1909.
2. Chile Time (CLT) applies to times in the America/Santiago zone during standard time periods since 1910-01-01.
3. Chile Summer Time (CLST) applies to times in the America/Santiago zone during daylight saving time periods since 1910-01-01.
4. Mataveri Mean Time (MMT) applies to times in the Pacific/Easter zone from 1890 to 1932-08-31.
5. Easter Island Time (EAST) applies to times in the Pacific/Easter zone during standard time periods since 1932-09-01.
6. Easter Island Summer Time (EASST) applies to times in the Pacific/Easter zone during daylight saving time periods since 1932-09-01.

References:

The Servicio Hidrográfico y Oceanográfico de la Armada (Army Hydrographic and Oceanographic Service) has a time change history  page showing every official time change since 1900. The text of past decrees governing these time changes is on this frequently asked questions  page. Both are in Spanish.