Understanding EST and MST
EST stands for Eastern Standard Time, UTC−5, used in Eastern North America. MST stands for Mountain Standard Time, UTC−7, used in Mountain North America. These are specific offset definitions, not automatic substitutes for the local time in a city.
How do you convert EST to MST?
Subtract the source offset from the destination offset: -420 − (-300) = -120 minutes. Subtract 120 minutes from the EST time. For example, 9:00 AM EST is 7:00 AM MST (same day). If the result crosses midnight, the calendar day changes too.
Does daylight saving time change this conversion?
The difference between these named offsets is fixed. A location may switch to a different abbreviation during daylight saving time, so an invitation saying “EST” can differ from the actual summer time in New York.
EST is always UTC−5. New York and most US Eastern locations use EDT (UTC−4) during daylight saving time.
MST is UTC−7. Many Mountain locations use MDT (UTC−6) in summer; most of Arizona stays on MST.
Which day does the converted time fall on?
“Previous day” means the destination is one calendar day before the source; “Next day” means one day after. Dates are relative to the day of your input time. A time-only conversion cannot determine a specific calendar date.