PST, PDT, and PT. There is a difference and it matters. (2024)

As a lifelong resident of Arizona, one might think that I have beensheltered to the silliness of Daylight Saving Time, DST. The State of Arizona, excluding the Navajo Nation, is one of the few places in the United States that does not intentionally move the hour hand of our clocks forward in the spring and back in the fall. Instead, we keep our clocks set to seven hours behind Coordinated Universal Time, UTC, 365.256 days per year. Unfortunately, this seems to really confuse peoplein places that change their clocks depending on the time of year. The issue became very apparent to me while working with a team that was split between Phoenix & Denver. You see Phoenix follows Mountain Standard Time, MST (UTC -7), all year round while Denver switches between Mountain Standard Time, MST (UTC -7), and Mountain Daylight Time, MDT (UTC -6), depending on the season. This caused a lot of confusion communicating meetings times, especially in the weeks leading up to theirclocks changing in the spring or in the fall. The biggest challenge was around the use of the term Mountain Standard Time and its abbreviation, MST, when the person really meant to communicate Mountain Daylight Time, MDT.

The solution was incredibly simple, for people in places that observe Daylight Saving Time, simply omit the words “standard” or “daylight” from your time zone vocabulary. For Arizona residents, that means communicating Pacific Time, PT, during the spring/summer months and Mountain Time, during the fall/winter months. For residents of states that observe Daylight Saving Time, omit “standard” or “daylight”.

• Pacific Standard Time = PST = UTC -8 hours, regardless of the date
• Pacific Daylight Time = PDT = UTC -7 hours
• Pacific Time = PT = either PST or PDT, depending on Daylight Saving Time rules
• Mountain Standard Time = MST = UTC -7 hours, regardless of the date
• Mountain Daylight Time = MDT = UTC -6 hours
• Mountain Time = MT = either MST or MDT, depending on Daylight Saving Time rules

When in doubt, omit the “standard” or “daylight” from your communications.