Atlantic Standard Time

Frequently asked questions

Common questions about AST, daylight saving, and how to handle it in software. Can't find what you need? Email [email protected].

Does every AST location skip daylight saving?

No. Most Caribbean territories—Anguilla, Antigua, Aruba, Barbados, Curaçao, and Dominica—stay on AST permanently. However, six Canadian and Atlantic-coast communities (for example America/Blanc-Sablon and America/Glace_Bay) spring forward to UTC-03:00 during the northern hemisphere’s DST window.

Why is AST sometimes written as UTC-04:00 and other times UTC-03:00?

The four-hour offset is the year-round baseline. When a member zone observes DST, clocks shift one hour forward—so AST becomes UTC-03:00 for those months. The UI tables above show the exact status for each zone.

Is AST the same as Eastern or Caribbean time?

They overlap but aren’t identical. Eastern Standard Time is also UTC-05:00 standard / UTC-04:00 daylight, while Caribbean zones like AST typically don’t observe any changes—making AST a more predictable choice for regional calendars.

Which countries actually use AST without any offset shift?

Public records list Anguilla, Antigua and Barbuda, Aruba, Barbados, Curaçao, and Dominica as the current ‘no-shift’ members—all holding the -04:00 offset permanently, so your scheduled calls won’t jump mid-year.

Why is Blanc-Sablon (Canada) showing a different offset today?

Blanc-Sablon is one of the few AST-labeled zones that fully adopts Canada’s daylight schedule. From late March onward, it switches to UTC-03:00 to match Atlantic Daylight Time, before stepping back to -04:00 in early November.

How did 30+ zones end up under AST?

Historically, the Atlantic Time label linked maritime provinces to Caribbean trading partners that preferred a fixed 240 minute gap from UTC. Over the 20th century, various island governments chose not to shift their clocks while neighborly Canadian zones did, creating the mix we see today.

What should global teams agree on to avoid confusion?

Use region-level identifiers rather than common abbreviations. Write ‘America/Glace_Bay’ or ‘America/Curacao’ in every invite—this avoids the one-letter difference between AST standard and AST-summer-time and prevents double-bookings.

Does AST observe daylight transitions for the Caribbean islands?

No. All six Caribbean jurisdictions mandated permanent Atlantic Standard Time after World War II. Today, AST clocks in the Caribbean never move, making them ideal anchors for cross-border meetings.

Is AST used for air-traffic or shipping control while DST is in effect?

Aviation and maritime systems commonly use UTC-based references (Zulu time) and post a time-zone alias for cabin announcements. So even when Blanc-Slabon springs to -5 EDT, traffic control still publishes its plain offsets.