MST to EST Converter (and EST to MST)

About this tool

This converter moves between Mountain Time and Eastern Time in either direction, with one extra choice that matters: whether the Mountain side is a place that changes its clocks, like Denver, or Arizona, which stays on Mountain Standard Time all year. It opens at 10:00 AM Mountain on today's date, shows the right abbreviation for each side (MST or MDT, EST or EDT), and runs a live clock for both places. A printable chart with Denver and Arizona columns, the dates when the Arizona gap changes, and a table of shared office hours follow the tool.

How to use it

1. Pick the Mountain location. Choose Denver for Colorado, Utah, New Mexico, Montana, Wyoming and the other places that switch to daylight time. Choose Phoenix for most of Arizona.
2. Pick a direction, Mountain to Eastern or Eastern to Mountain.
3. Enter the date and time. With Phoenix selected, the date decides whether the answer is 2 or 3 hours later.
4. Read the result, which spells out both offsets and the gap on that date. Use Swap direction to check the reverse.

Two different kinds of Mountain Time

Mountain Standard Time is UTC-07:00 and Eastern Standard Time is UTC-05:00. Under 15 U.S.C. 260a, daylight saving time runs from 2:00 a.m. on the second Sunday of March to 2:00 a.m. on the first Sunday of November, so Denver moves to MDT (UTC-06:00) when New York moves to EDT (UTC-04:00). The gap stays at 2 hours all year. The only exceptions are two short overnight windows on Sun Mar 8, 2026 and Sun Nov 1, 2026, when one city has switched and the other has not yet; the converter handles them for you.

The same law lets a state that lies entirely in one time zone exempt itself and stay on standard time. Arizona does: according to the Pima County Public Library, the state tried daylight saving time in 1967, the legislature rejected it in 1968, and Arizona has stayed on Mountain Standard Time since. The exception is the Navajo Nation in the northeast of the state, which, as its Office of the President and Vice President explains, does observe daylight saving time to stay in step with Navajo communities in Utah and New Mexico. For a place such as Window Rock, choose Denver in the converter.

Because New York changes and Phoenix does not, the Phoenix to New York gap is 2 hours from November to March and 3 hours from March to November. In summer Arizona clocks match California; in winter they match Denver. In 2026 the switches fall on Sun Mar 8, 2026 and Sun Nov 1, 2026; in 2027 on Sun Mar 14, 2027 and Sun Nov 7, 2027. A standing 10:00 AM Phoenix call therefore moves from noon to 1:00 PM on New York calendars each March.

Worked example: 10 AM Mountain

The default input is 10:00 AM with Denver selected. On a summer date the converter prints 10:00 AM MDT = 12:00 PM EDT, with offsets UTC-06:00 and UTC-04:00 and the note that Eastern Time is 2 hours ahead. Switch the location to Phoenix on the same date and the line becomes 10:00 AM MST = 1:00 PM EDT, 3 hours apart, at UTC-07:00 and UTC-04:00. On a January date both locations give 10:00 AM MST = 12:00 PM EST.

Common mistakes

• Treating "MST" as one zone. In July, MST describes Arizona only; Denver is on MDT, and the two are an hour apart.
• Keeping a summer calendar entry for a Phoenix client at a 2-hour offset. From March to November it is 3 hours.
• Assuming everyone in Arizona skips daylight saving time. The Navajo Nation does not.
• Hardcoding UTC-7 for Denver. Store America/Denver or America/Phoenix and let the time zone database decide.

Use cases

Booking calls between East Coast offices and teams in Denver, Salt Lake City, Boise, Albuquerque, Phoenix or Tucson; working out when an Eastern-time webinar starts in Arizona; checking whether a 5:00 PM Eastern deadline is 3:00 PM or 2:00 PM for an Arizona colleague. Related pages: PST to CST, CST to EST and PST to EST. For three or more cities, the Time Zone Converter adds a meeting planner.