AST time now (Atlantic Standard Time)

What AST means

AST stands for Atlantic Standard Time, UTC−4. It is used in the Canadian Maritimes, Puerto Rico and the eastern Caribbean.

It is a standard (winter) time. Places on AST that observe daylight saving time switch to ADT (UTC−3) in summer, so AST is a fixed offset while the local clock is not.

AST is ambiguous. It also means Arabia Standard Time (informal) (UTC+3, Saudi Arabia, Iraq, Kuwait, Qatar and their neighbours). This page shows UTC−4, the meaning English searchers usually want.

Where and when AST is used

4 zones use AST all year. 6 zones use it for part of the year only, switching to daylight saving time in the other months. Computed from tzdata under the current rules.

Other meanings of AST

When a time arrives with only these letters, look at where the sender is, or ask for the UTC offset. Calendars and programs should never guess a zone from an abbreviation: the IANA database’s own documentation calls abbreviations ambiguous in practice.

How long AST has been used

In the tzdata record, San Juan has used AST since 1899, Sydney has used AST since 1902 and Halifax has used AST since 1902.

AST in the past

Zones whose tzdata history shows AST before 2025 but that no longer use it:

• America/Grand_Turk (Providenciales): 2015–2018
• America/Miquelon (Saint-Pierre): 1911–1980
• America/Anchorage (Anchorage): 1900–1967

AST converted to other zones

Every column is a fixed offset, so this table is valid on any date. Remember that the regions behind some columns switch to summer time (EST to EDT, CET to CEST, GMT to BST); the clock in those cities is then an hour later than the column.

Related zones and conversions

• ADT time
• America/Halifax time zone
• UTC−4 time
• Time zones of the world
• Daylight saving time
• Time zone converter