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Everything About Time Zones
Articles covering the basics, clock changes, scheduling across time zones, and the technical details behind how computers handle time.
What Is Daylight Saving Time?
Daylight saving time shifts clocks forward by one hour in spring and back in fall. Here's what it is, when it happens, and which countries observe it.
Clock ChangesWhy Does Daylight Saving Time Exist?
DST was invented to save energy and make better use of daylight hours. But does it actually work? Here's the full history and modern evidence.
Clock ChangesWhich Countries Use Daylight Saving Time?
About 70 countries observe DST — but most of the world doesn't. Here's a breakdown of who changes their clocks and who doesn't, and why.
Clock ChangesEST vs EDT: What's the Difference?
EST is Eastern Standard Time (UTC−5). EDT is Eastern Daylight Time (UTC−4). Here's when each applies and which US states use them.
Clock ChangesPST vs PDT: What's the Difference?
PST is Pacific Standard Time (UTC−8). PDT is Pacific Daylight Time (UTC−7). Here's the full breakdown of when each is active and which regions use them.
Clock ChangesCST vs CDT: What's the Difference?
CST is Central Standard Time (UTC−6). CDT is Central Daylight Time (UTC−5). Here's who uses them and when they switch.
Clock ChangesMST vs MDT — and the Arizona Exception
MST is Mountain Standard Time (UTC−7). MDT is Mountain Daylight Time (UTC−6). But Arizona stays on MST year-round — with one famous exception.
Clock ChangesWhen Does Daylight Saving Time Start and End?
DST dates differ between the US, Europe, and the Southern Hemisphere. Here are the exact rules and how to find out when your region's clocks change.
Clock ChangesUS States That Don't Observe Daylight Saving Time
Arizona and Hawaii don't change their clocks. Here's the full list of US states and territories that stay on standard time year-round and why they opted out.
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