AST — which one do you mean?
AST means 2 different things, and they are
hours apart. If you received a timestamp labelled AST, the sender's
location decides which of these applies — pick it below.
Atlantic Standard Time · North America
21:15:45
Wednesday, 12 August 2026
- abbreviation denotes
- -04:00
- in force right now
- ADT (UTC-03:00) · DST
- use in code
- America/Halifax
- also valid
- America/Puerto_Rico
- next clock change
- 1 Nov 2026 01:00 → AST
Right now this zone is on ADT, not AST —
they are the same place at different times of year.
Arabia Standard Time · Asia
03:15:45
Thursday, 13 August 2026
- abbreviation denotes
- +03:00
- in force right now
- UTC+03:00 (UTC+03:00)
- use in code
- Asia/Riyadh
- also valid
- Asia/Baghdad, Asia/Qatar
- next clock change
- none — fixed offset
Right now this zone is on UTC+03:00, not AST —
they are the same place at different times of year.
Use the IANA name, not the abbreviation
Python
from datetime import datetime
from zoneinfo import ZoneInfo
# right: an IANA zone carries the full history of rule changes
now = datetime.now(ZoneInfo("America/Halifax"))
print(now.isoformat(), now.tzname())
# wrong: an abbreviation is not resolvable, and a hard-coded offset
# silently rots the next time the rules change
# now = datetime.now(timezone(timedelta(hours=...))) # don'tAST questions
What does AST stand for?
AST has 2 distinct meanings in active use: Atlantic Standard Time (-04:00, America/Halifax); Arabia Standard Time (+03:00, Asia/Riyadh). Which one applies depends entirely on who wrote the timestamp.
What time is it in AST right now?
Atlantic Standard Time: 21:15 on Wednesday (ADT); Arabia Standard Time: 03:15 on Thursday (UTC+03:00).
Which IANA timezone should I use instead of AST?
America/Halifax for Atlantic Standard Time, Asia/Riyadh for Arabia Standard Time. Date libraries cannot resolve bare abbreviations, and an abbreviation carries no daylight-saving history, so a stored offset silently rots when a government changes the rules.
Why does my computer show ADT instead of AST?
Because America/Halifax is currently on ADT (UTC-03:00), its daylight-saving variant. AST (-04:00) applies during the other half of the year. Both names refer to the same place, one hour apart.