GMT to MST Time Zone Converter
This converts London time (GMT in winter, BST in summer) to US Mountain Time — Denver, Salt Lake City, Phoenix. Mountain runs 7 hours behind London for most of the year. Both sides observe daylight saving but switch on different dates, so the gap is briefly off by an hour each spring and fall. The tool applies the right offset for your date.
Enter a date and time to convert.
Daylight saving is applied automatically for the date you pick. Labels like PST/EST name the zone (Pacific/Eastern); the real abbreviation shifts to PDT/EDT during daylight saving, and gmt here means London (GMT in winter, BST in summer) while utc stays fixed.
The time difference
US Mountain Time usually sits 7 hours behind London — subtract 7 from the London clock. Both regions observe daylight saving, so most of the year they move together and the 7-hour gap holds steady. They just don't switch on the same day: the US changes a few weeks apart from the UK, so during two short windows the difference drops to 6 hours before settling back to 7.
A worked example
Take 9:00 AM in London. On January 15, 2026 (winter), that is 2:00 AM MST in Denver. On July 15, 2026 (summer), it's still 2:00 AM MDT — the usual 7-hour gap holds at both anchor dates. That's the middle of the night out west, and still the same calendar day.
Daylight saving & the abbreviation caveat
"GMT" here is London's clock — GMT in winter, BST in summer. "MST" is really Mountain Time year-round: MST in winter, MDT (Mountain Daylight Time) in summer, and locals just say MT. The US switches on March 8 and November 1, 2026, while London switches on March 29 and October 25. Because those dates don't match, the gap is briefly off by an hour in late March and late October. One extra wrinkle: Arizona skips daylight saving entirely. The converter accounts for the exact offset on your chosen date, so a 6-hour result during one of those windows is expected.
When you'll use it
Useful for calls with teams in Denver or Salt Lake City, timing a ski-resort or outdoor-event stream, or coordinating with a US company headquartered in the Mountain zone. Because Mountain sits deep in the American morning when London is at work, finding an overlapping hour takes a little planning — this shows you exactly where it lands.
Frequently asked questions
How many hours behind London is US Mountain Time?
Seven hours for most of the year. When it's 12:00 noon in London it's 5:00 AM in Denver. The gap only shifts by an hour during the short windows when the US and UK clocks are out of step.
What's the difference between MST and MDT?
MST is the winter name; from mid-March to early November most of the Mountain zone moves to Mountain Daylight Time (MDT). Locals just call it Mountain Time, or MT. (Arizona is the odd one out — it stays on MST all year.)
When is the gap not exactly 7 hours?
During March 8–29 and October 25–November 1, 2026. The US and UK change clocks on different dates, so for those short stretches Mountain is 6 hours behind London instead of 7.