How often time zones change
Between 1970 and 2026 the 312 zones in the tz database changed their standard time 459 times, about 8 a year on average. The changes come in bursts: 1991 alone had 57 and 1992 another 42, while 1 of the 57 years had none.
What counts as a change
This article counts changes of standard time: moments when a zone’s base offset from UTC was set to a new value. The yearly move into and out of summer time is not counted, because it does not change the base offset. Seasonal moves are far more common. Across all zones the clocks jumped 15,476 times between 1970 and 2026, almost all of them for daylight saving time, so changes of standard time make up only a small share of all clock changes.
Changes of standard time per year, 1970 to 2026
The two busiest years are highlighted.
The busiest years
The top of the table is dominated by a few countries with many zones that changed together. In 1991 and 1992, 78 percent of the changes were in Russia and other former Soviet republics. Russia appears again in 2011, when 28 of its zones moved to a new standard time, and in 2014, when 22 moved back by an hour. The other years in the table are led by Argentina and Russia.
| Year | Changes | Zones by country |
|---|---|---|
| 1991 | 57 | Russia (27), Argentina (14), Kazakhstan (7) and United States and others |
| 1992 | 42 | Russia (24), Kazakhstan (9), Nicaragua (2) and Portugal (2) and others |
| 2011 | 33 | Russia (28), Antarctica (2), Belarus and Samoa and others |
| 2014 | 25 | Russia (22), Ukraine (2) and Papua New Guinea |
| 2000 | 23 | Argentina (12), Canada (5), Dominican Republic (2) and South Sudan and others |
| 2004 | 23 | Argentina (16), Kazakhstan (5), Russia and Georgia |
| 1999 | 17 | Argentina (12), Canada (2), Kazakhstan and Lithuania and others |
| 2016 | 15 | Russia (9), Antarctica (2), Venezuela and Chile and others |
By decade, the 1990s stand out with 153 changes, followed by the 2010s with 110. The 1970s had 36, the 1980s 57 and the 2000s 73. The 2020s have had 30 so far, including the 6 changes recorded for 2026.
The zones that changed most
A small number of zones account for a large share of the total. Casey Station has changed its standard time 16 times since 1970, more than any other zone; the research station’s record switches back and forth between UTC+8 and UTC+11. Next come San Luis (8), Qyzylorda (8), Volgograd (7) and Libya (6).
Counted by country, Russia leads with 130 changes across its zones, ahead of Argentina (60), Kazakhstan (39) and United States (29). These totals add up the changes of each zone, so a single national decision applied to 20 zones counts 20 times.
Spread across zones, the changes are uneven. 60 zones changed their standard time exactly once since 1970, 36 changed it twice, and 68 changed it three times or more. The zones with many changes are concentrated in a few countries, which is why the national totals above are dominated by Russia, Argentina and Kazakhstan.
The zones that never changed
At the other end, 148 of the 312 zones, close to half, have kept the same standard time throughout the period. By region the largest groups of them are in North America (36), Oceania (28) and Asia (26). Some of these zones never moved their clocks at all; others, such as most European zones, kept their standard time but moved their clocks every summer.
Stability in standard time does not mean stable clocks. France has kept UTC+1 as standard time since 1945 and still moves its clocks twice a year, while Japan has kept UTC+9 without any change at all since 1888.
Forward or back, and by how much
Of the 459 changes, 245 moved standard time forward and 214 moved it back. Most were a single hour: 405 changes, or 88 percent. 17 were half an hour or less, 10 were two hours, and 24 were three hours or more. The largest are the date-line moves of the Pacific, where a zone switched from one side of the line to the other: Marshall Islands in 1993, Kanton Island in 1994, Kiritimati in 1994, Tokelau in 2011 and Samoa in 2011, each a jump of a full day.
The most recent changes
Since 2020 the database has recorded 30 changes of standard time. They include Casey Station (2020), Dawson (2020), Volgograd (2020), South Sudan (2021), Casey Station (2021), Casey Station (2022), Syria (2022), Jordan (2022), Chihuahua (2022), Casey Station (2023), Nuuk (2023) and Almaty (2024). Several of the 2026 entries are summer offsets made permanent, so the clocks did not move on the day the change took effect.
Using the record
Every change counted here is listed with its date on the year-by-year list of standard time changes, and in the standard time table of each zone. A change of standard time is the most common reason that an old timestamp converts differently from a new one, so for any date before the latest change in a zone, the converter uses the offset that applied then.
Source: IANA Time Zone Database, release 2026f (public domain), computed by this site; see about the data for definitions. Look up any zone in the converter.