Rules currently in force

Mongolia observed daylight saving time prior to 2007. The Mongolian parliament canceled it in February 2007, and reinstated it beginning in March 2015. Source [7] adds that DST was in effect from 1983 to 1999, and then again starting in 2001.

There have been conflicting reports about Mongolia's time zones. The geographical extent of the time zones, and the duration of daylight saving time, are all questionable. Recently (May 2005), there have been a number of messages on the tz mailing list reporting a change. Some Internet time zone sites follow the tz database standard; therefore, they show Mongolia divided into three time zones as listed in the following table. Three Mongolian travel sites (Mongolian Tourism Association, Mongolian Airlines, and Tsolmon Travel), and the site of the Mongolian Embassy in the U.S., all say that Mongolia has two time zones, with the western zone consisting of Bayan-Ölgiy, Hovd, and Uvs provinces. When the UB Post online newspaper reported the date for the beginning of DST in March 2005, a reader wrote that there are four time zones, with Sühbaatar province on UTC+8.5 standard time. He added, "The [Sühbaatar] timezone is new this year, it is one of the few things the new parliament passed during the tumultous winter session." The OAG and the CIA World Factbook show only one time zone covering all of Mongolia, as they have done for years. It has been reliably reported (c. 2008) that the former Choibalsan time zone had moved to UTC+8. It's still not clear whether Choibalsan actually observed UTC+9 before then. More recently, the CIA World Factbook is showing two time zones in Mongolia, UTC+7 and UTC+8.

In summary, the opinions that have come forth are that Mongolia has: (a) one time zone, UTC+8; (b) two time zones, UTC+7 and UTC+8; (c) three time zones, UTC+7, UTC+8, and UTC+9; or (d) four time zones, UTC+7, UTC+8, UTC+8.5, and UTC+9. All time zones observed DST in the summer, through 2006. Parliament canceled DST for 2007. If there is a UTC+7, it covers Bayan-Ölgiy, Hovd, and Uvs provinces, and possibly Dzavhan and Govi-Altay. If there is a UTC+8.5, it covers Sühbaatar. If there is a UTC+9, it applies to Dornod and Sühbaatar (unless the latter is in UTC+8.5).

I continue to report the time zones as listed in the tz database.

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".

Find the Rule and Standard Time for the given time and date.

Apply the Rule, using the Standard Time for the given time and place.

Time zone names

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

1. Times in the Asia/Choibalsan zone are designated Choibalsan Time (CHOT), or Choibalsan Summer Time (CHOST) when daylight saving is in effect.
2. Times in the Asia/Hovd zone are designated Hovd Time (HOVT), or Hovd Summer Time (HOVST) when daylight saving is in effect.
3. Times in the Asia/Ulaanbaatar zone are designated Ulaanbaatar Time (ULAT), or Ulaanbaatar Summer Time (ULAST) when daylight saving is in
effect.

Sources:

1. [1] Mongolian Tourism Association (http://www.travelmongolia.org/travel.mongolia/travel.info.html, dead link, retrieved 2005-05-20)
2. [2] Mongolian Airlines (http://www.miat.com/frame.php?page=travel_information, dead link, retrieved 2005-05-20)
3. [3] Tsolmon Travel (http://www.tsolmontravel.com/eng/info.htm, dead link, retrieved 2005-05-20)
4. [4] Reader comments in response to an article in the UB Post (http://ubpost.mongolnews.mn/index.php?subaction=showcomments&id=1111634894&archive=&start_from=&ucat=1&, dead link, retrieved 2005-05-20)
5. [5] Mongolian Embassy to the United States (http://www.mongolianembassy.us/eng_tourism/tourism.php, dead link, retrieved 2005-05-20)
6. [6] UB Post  online newspaper (retrieved 2008-11-01)
7. [7] Info Mongolia  site (retrieved 2015-07-03)