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UTC−07:00: blue (January), orange (July), yellow (year-round), light blue (sea areas)

Key Information

Time in Nunavut
  Standard DST
GMT−05:00 GMT−04:00 Eastern Time
GMT−05:00 (year round) Eastern Time
GMT−06:00 GMT−05:00 Central Time
GMT−07:00 GMT−06:00 Mountain Time
Time in Mexico
Mexican time zone Standard DST U.S. equivalent
Zona Sureste UTC−05:00 Eastern Standard Time
Zona Centro UTC−06:00 UTC−05:00 Central Time
UTC−06:00 Central Standard Time
Zona Pacífico UTC−07:00 UTC−06:00 Mountain Time
UTC−07:00 Mountain Standard Time
Zona Noroeste UTC−08:00 UTC−07:00 Pacific Time

UTC−07:00 is an identifier for a time offset from UTC of −07:00. In North America, it is observed in the Mountain Time Zone during standard time, and in the Pacific Time Zone during the other eight months (see daylight saving time). Some locations use it year-round.

As standard time (Northern Hemisphere winter)

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Principal cities: Denver, Salt Lake City, Calgary, Ciudad Juárez

North America

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As daylight saving time (Northern Hemisphere summer)

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Principal cities: Los Angeles, Vancouver, Tijuana

North America

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As standard time (year-round)

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Principal cities: Phoenix, Hermosillo

North America

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References

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Revisions and contributorsEdit on WikipediaRead on Wikipedia

UTC−07:00

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UTC−07:00 is a time offset from Coordinated Universal Time (UTC) that subtracts seven hours, serving as the standard time designation for regions in the Mountain Time Zone of North America. This offset is legally defined under the U.S. Standard Time Act and Uniform Time Act of 1966, placing it as the fourth time zone west of the Atlantic, encompassing areas west of the Central-Mountain boundary and east of the Mountain-Pacific boundary. In practice, it applies during standard (non-daylight saving) periods, with locations in the United States and Canada advancing to UTC−06:00 during daylight saving time from the second Sunday in March to the first Sunday in November. The Mountain Time Zone, utilizing UTC−07:00 as Mountain Standard Time (MST), covers several fully enclosed U.S. states including , , , , , and , as well as portions of , , , , , , and . In Canada, it includes the entirety of and Saskatchewan's area, along with parts of , , and . Mexico employs this offset in states such as , Chihuahua, , and , which since the abolition of in 2022 generally observe UTC−07:00 year-round (with limited exceptions in some northern border municipalities). Notable exceptions to daylight saving observance include most of (except the ) and most of , which maintain UTC−07:00 year-round. This time zone supports commerce, transportation, and daily coordination across diverse geographies, from the to border regions, with boundaries occasionally adjusted by the U.S. for economic efficiency. Its implementation ensures synchronization with UTC for global activities like and , where UTC−07:00 equates to Zulu time minus seven hours.

Introduction and Basics

Time Offset

UTC−07:00 denotes a time zone offset that places local time exactly 7 hours behind (UTC), expressed as UTC−07:00 or equivalently −07:00. This offset is applied by subtracting 7 hours from UTC to determine the corresponding . The offset aligns roughly with mean along the 105th meridian west of the , where the produces a natural 7-hour lag relative to (GMT), which closely corresponds to UTC. For instance, if the UTC time is 12:00, the in UTC−07:00 is 05:00, illustrating the straightforward arithmetic of local time = UTC time − 7 hours. This offset is commonly designated by abbreviations such as MST (Mountain Standard Time) during standard time periods or during daylight saving time adjustments in applicable regions.

Designations and Abbreviations

UTC−07:00 is officially designated as Mountain Standard Time (MST) when used as standard time in the Mountain Time Zone. It is also known as when applied as daylight saving time in the . The abbreviation MDT (Mountain Daylight Time) does not apply to UTC−07:00, as it corresponds to UTC−06:00. Informally, UTC−07:00 may be referred to generically as "Mountain Time" in contexts encompassing both standard and daylight variants of the Mountain zone, though this term is not specific to the offset. The etymology of "Mountain" in MST derives from the , which span the primary region where this standard time is observed. Similarly, "Pacific" in PDT originates from the Pacific coastal areas where the daylight saving offset is implemented. In international standards, UTC−07:00 is denoted in ISO 8601 format as -07:00, representing the offset from . The (IANA) time zone database uses identifiers such as America/Denver for locations observing MST at UTC−07:00 and America/Los_Angeles for those using PDT at the same offset.

Seasonal Usage

As Standard Time (Non-DST Periods)

UTC−07:00 serves as the standard time offset for the Mountain Time Zone during periods when is not observed, commonly abbreviated as Mountain Standard Time (MST). This offset is applied across regions in the United States and that fall within the zone, ensuring synchronized timekeeping for daily activities, transportation, and commerce during the winter months. The period typically spans from early to mid-March, aligning with the seasonal reduction in daylight hours in the . In the and , this phase begins when clocks are set back one hour from Mountain Daylight Time, restoring as the local standard. For example, in 2025, the transition occurred on November 2, the first Sunday of the month, at 2:00 a.m. local daylight time, shifting to 1:00 a.m. . This period ends the following spring when resumes, advancing clocks forward to UTC−06:00. Key locations observing UTC−07:00 as standard time include the U.S. state of Colorado and the Canadian province of Alberta. These areas, among others in the Mountain Time Zone, revert to this offset annually during non-DST months to maintain consistency with regional solar patterns and economic ties. The primary purpose of UTC−07:00 in this context is to approximate mean solar time along the 105th meridian west longitude, where clock noon closely corresponds to the sun's highest point in the sky. This alignment helps minimize discrepancies between civil time and natural light cycles, with variations from true solar time reaching up to 30 minutes at the zone's eastern and western boundaries due to the 15-degree longitudinal span of the time zone.

As Daylight Saving Time (DST Periods)

UTC−07:00 serves as the daylight saving time offset in the , where it is designated as Pacific Daylight Time (PDT) and observed by advancing clocks one hour forward from Pacific Standard Time (PST, ). This adjustment aligns local time with the standard during the summer months, effectively shifting the entire daily schedule to capture more evening daylight. The primary locations observing UTC−07:00 as PDT include coastal U.S. states such as and Washington, along with parts of in and in . These areas, spanning the , transition to this offset to synchronize with regional daylight patterns, encompassing major urban centers and extending to portions of , , and in the United States. The core purpose of adopting during daylight saving periods is to extend evening daylight hours by advancing clocks, thereby promoting greater utilization of after typical work or school hours. This practice originated in the early as an measure, initially implemented during to reduce reliance on artificial lighting and fuel, a rationale that influenced its widespread adoption in . In the United States and , the transition to UTC−07:00 as PDT begins at 2:00 a.m. on the second in , with clocks advancing one hour forward; for example, this occurred on March 9, 2025. The period ends at 2:00 a.m. on the first in , when clocks are set back one hour to revert to . This schedule, harmonized across most observing regions since 2007, ensures a consistent seven-month duration for daylight saving observance.

Year-Round Usage

Locations Observing UTC−07:00 Continuously

The primary locations observing UTC−07:00 on a continuous basis, without transitions to , are the majority of the U.S. state of (excluding the ), the within , the Mexican state of , the Territory in Canada, and select municipalities in , Canada, such as Creston and the East Kootenay region. These areas maintain Mountain Standard Time (MST) equivalent year-round, applying uniformly to entire jurisdictions or municipalities without seasonal adjustments. Arizona's exemption from daylight saving time stems from a 1968 legislative decision to prioritize solar time alignment and avoid clock changes amid the state's intense summer heat, a policy rooted in the Uniform Time Act of 1966 that permitted opt-outs. Similarly, Sonora discontinued in 1999 to synchronize economically and temporally with neighboring Arizona, facilitating cross-border and . In Yukon, the shift to permanent UTC−07:00 occurred in 2020 following public consultations, aiming to simplify scheduling and reduce disruptions from biannual clock shifts. The specified British Columbia areas adopted year-round MST for comparable reasons of consistency with local solar patterns and minimal economic impact from time changes. As of November 2025, these observances remain unchanged, with no federal or territorial mandates altering the . Arizona continues to maintain its longstanding exemption from , with ongoing legislative debate but no enacted changes to adopt it. Yukon's policy, formalized by territorial law in 2020, continues without reversal, supported by ongoing resident feedback favoring stability. Sonora's alignment with Arizona has held steady post-Mexico's 2022 nationwide abolition of daylight saving time outside border zones.

Exceptions and Variations

Within the broader application of UTC−07:00 as Mountain Standard Time (MST) in , notable exceptions arise from jurisdictional decisions by Native American tribes in . The , spanning parts of , , and , observes (DST), utilizing UTC−07:00 during standard time periods and advancing to (Mountain Daylight Time, MDT) from to . This creates a patchwork effect, as the majority of remains on UTC−07:00 year-round without DST observance. Complicating this further is the , an enclave geographically surrounded by the but administratively independent. The do not observe DST, maintaining UTC−07:00 throughout the year regardless of the surrounding Navajo's seasonal shift to UTC−06:00. This results in localized time discrepancies along reservation borders, such as U.S. Highway 160 in northeastern , where travelers may cross time zones within a short distance. These tribal variances represent key North American irregularities for , primarily confined to Arizona's interior dynamics rather than international borders. As of November 2025, no federal changes to DST policies have been enacted , though Arizona's continues to debate potential adoption of DST to align more closely with neighboring regions.

Regional Details

United States and Canada

In the , UTC−07:00 is observed as Mountain Standard Time (MST) across six states in their entirety—, , , , , and —and portions of eight others, including , , , , , , , and . This zone spans the Rocky Mountain region and adjacent areas, facilitating synchronization for commerce and transportation. Additionally, UTC−07:00 serves as Pacific Daylight Time (PDT) during (DST) periods in the , which encompasses , Washington, most of , the western portion of , and northern . Federal law under the mandates DST observance in the United States, advancing clocks by one hour from the second Sunday in to the first Sunday in , thereby shifting the Mountain Time Zone to (MDT) and the to UTC−07:00 (PDT) during those months. , however, has opted out of DST statewide since 1968, remaining on MST year-round except in the , where DST is observed to align with neighboring states. The extended DST by approximately one month—starting the second Sunday in and ending the first Sunday in —effective from 2007, with no subsequent alterations to these dates. For 2025, DST in applicable areas ends on November 2, reverting to , and resumes on 8, 2026. In Canada, UTC−07:00 corresponds to Mountain Standard Time in Alberta, the entirety of the Northwest Territories, most of western Nunavut, southeastern portions of British Columbia, and select areas of Saskatchewan such as around Lloydminster. These regions observe DST from the second Sunday in March to the first Sunday in November, aligning with U.S. practices to support cross-border economic activities, as governed by provincial and territorial legislation harmonized under federal guidelines. Consequently, Mountain Daylight Time (MDT, UTC−06:00) applies during DST periods, while Pacific Daylight Time (PDT, UTC−07:00) is used in British Columbia's coastal areas and Yukon during the same interval. For 2025, DST ends on November 2 in these jurisdictions, with the next transition occurring on March 8, 2026.

Mexico

In Mexico, UTC−07:00 is primarily observed in northwestern regions as part of the country's alignment with North American time standards, particularly following the nationwide abolition of (DST) in 2022. The federal government, through the Secretaría de Energía, enacted reforms to eliminate DST across most of the nation effective October 30, 2022, transitioning areas to permanent to promote energy savings and reduce disruptions. However, exceptions persist for northern border municipalities to maintain synchronization with adjacent U.S. time zones, facilitating cross-border commerce and daily interactions. The states of , , , and observe UTC−07:00 year-round as permanent Mountain Standard Time, without DST observance, to support economic ties and regional consistency. This policy, unchanged post-2022 reforms, covers entire states including major cities like in and in . In Chihuahua, UTC−07:00 applies specifically to border municipalities adjacent to U.S. Mountain Time areas, such as , which shares a boundary with . These locales use UTC−07:00 as but continue DST observance, advancing clocks to from the second Sunday in March to the first Sunday in November, to mirror U.S. practices and ease trade across the Paso del Norte region. In contrast, the majority of Chihuahua adopted permanent after the 2022 abolition, highlighting state-level geographic distinctions driven by proximity to the border. As of 2025, UTC−07:00 remains the fixed offset in , , , , and the specified Chihuahua border areas, with no federal plans for reversion or further adjustments, solidifying these zones' role in Mexico's post-DST framework.

History

Establishment of Time

The establishment of the Time Zone traces its origins to the late , when rapid railroad expansion across created chaos from varying local times based on solar observations. On November 18, 1883, American and Canadian railroads collaboratively introduced four continental zones—Eastern, Central, , and Pacific—to synchronize operations and eliminate scheduling discrepancies affecting thousands of local times. The Time Zone was defined by the mean at the 105th meridian west of Greenwich, establishing an initial offset of seven hours behind (GMT-07:00). This railroad initiative, proposed by Canadian engineer and refined through conventions like the 1883 General Time Convention, was voluntarily adopted by most communities, though not yet legally mandated. In the United States, the need for federal oversight grew with interstate commerce and exigencies, leading to the of 1918 (also known as the Calder Act). Signed into law on March 19, 1918, this legislation formally recognized the four railroad time zones, including Mountain Standard Time, and placed them under the Interstate Commerce Commission's supervision to ensure uniformity. The act defined Mountain Standard Time as GMT-07:00 for the zone encompassing states like , , and , effective immediately upon passage, marking the first nationwide legal standardization of time in the U.S. Canada followed a parallel path, with the 1883 railroad adoption providing the initial framework, but provincial governments gradually formalized alignment in the ensuing decades. By the late 1910s and early 1920s, most provinces, including those in the Mountain region like and parts of , had enacted laws or ordinances to enforce the standard zones, often in coordination with U.S. borders to facilitate cross-border trade and rail efficiency. This synchronization ensured that Mountain Time was consistently observed as GMT-07:00 in Canadian territories west of the Central zone. The offset for Mountain Time remained stable as GMT-07:00 until the international shift to (UTC) in 1972, when UTC—based on atomic clocks for greater precision—replaced GMT as the global reference without altering the seven-hour difference. This transition, formalized by the , preserved the practical application of the zone while enhancing accuracy for modern and .

Evolution of DST Policies

Daylight saving time (DST) was first introduced in the United States during through the of 1918, which established it nationwide from the last Sunday in March to the last Sunday in October for the years 1918 and 1919, affecting all time zones including the Mountain zone ( as standard time). This wartime measure aimed to conserve energy by extending evening daylight, but it proved unpopular due to disruptions in daily routines and agricultural schedules, leading to its repeal by in 1919, after which DST observance became a local option without federal mandate. During , President reinstated year-round DST, known as "War Time," effective February 9, 1942, until September 30, 1945, shifting the entire country—including the Mountain zone—forward by one hour continuously to support the war effort by saving fuel and aligning with production needs. Post-war, DST again reverted to voluntary local adoption, resulting in a of observances across states and zones that complicated interstate commerce and transportation. In the modern era, the addressed this inconsistency by standardizing DST nationwide, requiring it to begin on the last in April and end on the last in October unless a state opted out by a majority vote in both legislative houses, thereby promoting uniformity in the Mountain zone's transitions between (standard) and (daylight). This federal law, signed by President , built on earlier time zone regulations to facilitate while allowing exemptions for regions like parts of . Further evolution came with the , which extended DST by approximately one month—starting the second in March and ending the first in November—effective from 2007, with the goal of reducing energy consumption through additional evening daylight, directly impacting the periods when is observed in non-DST Mountain regions. The extension was projected to save about 0.03% of annual U.S. electricity use, though studies later debated its overall efficacy. Key policy changes have introduced variations in UTC−07:00 observance. In 1968, Arizona exercised its exemption under the Uniform Time Act, opting out of DST entirely after a brief trial period in 1967, citing the state's hot climate where extended evenings would exacerbate cooling demands rather than conserve energy, thus maintaining year-round UTC−07:00 (Mountain Standard Time) except on the Navajo Nation. Similarly, in Mexico, DST was abolished nationwide on October 30, 2022, via a decree from President Andrés Manuel López Obrador, eliminating clock changes to simplify life and reduce health disruptions; this shifted most areas to permanent standard times, such as UTC−07:00 in northern Mountain Time states like Chihuahua (except border municipalities, which continue to observe DST to align with the U.S.), affecting cross-border synchronization with U.S. Mountain regions. These decisions highlight how local priorities, such as climate and economic ties, have shaped deviations from uniform DST. As of November 2025, proposals under the seek to make DST permanent nationwide, which would establish as year-round time in the Mountain zone (effectively permanent MDT), aiming to eliminate biannual changes for health and productivity benefits; however, the bill (H.R. 139 and S. 29 in the 119th Congress) has not been enacted, stalling in committee without a floor vote. This ongoing debate reflects persistent tensions between standardization and regional preferences in DST policies affecting UTC−07:00.

References

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