Main Difference

In the United States and Canada, this time zone is generically called the Pacific Time Zone (PT). Specifically, it uses Pacific Standard Time (PST) when observing standard time (late autumn to early spring), and Pacific Daylight Time (PDT) when observing daylight saving time (early spring to late autumn).

What is PST?

Pacific Standard Time (PST) is 8 hours behind Coordinated Universal Time (UTC). This time zone is a standard time zone and is used in: North America. This time zone is often called Pacific Time.

What is PDT?

Pacific Daylight Time (PDT) is 7 hours behind Coordinated Universal Time (UTC). This time zone is a DST (daylight saving time) time zone and is used in: North America. This time zone is often called Pacific Daylight Time.

Key Differences

1. PDT is a daylight saving/summer time zone, in the winter some places will switch to the corresponding standard time zone: PST (Pacific Standard Time). Some places observe daylight saving time/summer time during the summer, and therefore use PDT (Pacific Daylight Time) in the summer.
2. An email sent from someone in the Pacific Daylight Time (PDT) time zone will have the time zone listed as “-0700” in the headers of the email. An email sent from someone in the Pacific Standard Time (PST) time zone will have the time zone listed as “-0800” in the headers of the email.
3. S. states using PST in the winter and PDT in the summer, California, Idaho – western counties Show, Nevada, Oregon – except most of Malheur county, Washington. U.S. states using PDT in the summer and PST in the winter, California, Idaho – western counties Show, Nevada, Oregon – except most of Malheur county, Washington.
4. Pacific Time is either Pacific Daylight Time or Pacific Standard Time. In some contexts Pacific Standard Time may be interpreted as including the possibility of a Daylight Time variant, in other contexts not. Pacific Daylight Time is always “summer time” and an hour different from the “winter” version of Pacific Standard Time.
5. Only some locations are currently on PST because most places in this time zone are currently on summer time / daylight saving time and are observing PDT.
6. When using PDT, time is moved one hour ahead while it is moved one hour behind back to its original time when PST is again used.
7. PDT is used to make use of the longer time of day during the summer in order to help conserve energy while PST is used during the winter which has shorter days than summer.
8. Both PST and PDT are used in places that observe Pacific Time (PT). Most parts of the world observe daylight saving time during the summer. Depending on where one is located, it is called by another name which is according to the time zone being used in that particular location.