Rules currently in force
It has been reliably reported (in the tz database) that the former Choibalsan time zone is now observing UTC+8. It's still not clear
whether Choibalsan actually used to observe UTC+9.
Ganbold writes that the Mongolian parliament has canceled daylight saving time for 2007.
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.
In summary, the prevailing opinions 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.
| Area | Standard | Zone Name |
|---|
| Bayan-Ölgiy, Dzavhan, Govi-Altay, Hovd, Uvs provinces | UTC+7 | Asia/Hovd |
| Dornod and Sühbaatar provinces | UTC+9 | Asia/Choibalsan |
| Rest of Mongolia | UTC+8 | Asia/Ulaanbaatar |
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.
| Zone Name | Rule | Standard Time | Final Date |
|---|
| Asia/Hovd | Local | | 1905-08-01 00:00 |
| | UTC+6 | 1978-01-01 00:00 |
| Mongol | UTC+7 | |
| Asia/Ulaanbaatar | Local | | 1905-08-01 00:00 |
| | UTC+7 | 1978-01-01 00:00 |
| Mongol | UTC+8 | |
| Asia/Choibalsan | Local | | 1905-08-01 00:00 |
| | UTC+7 | 1978-01-01 00:00 |
| | UTC+8 | 1983-04-01 00:00 |
| Mongol | UTC+9 | |
Apply the Rule, using the Standard Time for the given time and place.
| Rule | Years | Description |
|---|
| Local | All | Local Mean Solar Time |
| Mongol | Standard Time, with DST = Standard Time + 1:00 during the following periods: |
| 1983 | from April 1 at 00:00 to October 1 at 00:00 |
| 1984 | from April 1 at 00:00 to September 29 at 03:00 |
| 1985-1998 | from the last Sunday in March at 02:00 to the last Sunday in September at 03:00 |
| 2001 | from April 27 at 02:00 to September 28 at 02:00 |
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.
Times in the Asia/Choibalsan zone are designated Choibalsan Time (CHOT), or Choibalsan Summer Time (CHOST) when daylight saving is in effect.
Times in the Asia/Hovd zone are designated Hovd Time (HOVT), or Hovd Summer Time (HOVST) when daylight saving is in effect.
Times in the Asia/Ulaanbaatar zone are designated Ulaanbaatar Time (ULAT), or Ulaanbaatar Summer Time (ULAST) when daylight saving is in
effect.