Technical Specifications & Standards
Official chronometric properties, ISO standards, and international database registry identifiers for Atlantic Daylight Time:
Daylight Saving Time (DST) Transitions
⬆️ Spring Forward (Clocks Advance)
Second Sunday in March at 02:00 AM (Clocks advance from AST to ADT)
⬇️ Fall Back (Clocks Return)
First Sunday in November at 02:00 AM (Clocks return from ADT to AST)
Observing Jurisdictions & Subdivisions
3 Sovereign NationsSovereign nations, administrative subdivisions, and regional territories officially operating under ADT:
Regional Subdivisions & Territory Details
Financial Markets & Trading Hours
Maritime ports and reinsurance firms in Bermuda align their afternoon trading directly with opening bells on the Tokyo-to-London currency corridors.
Local Hours: 09:00 - 16:00 ADT
UTC Window: 12:00 - 20:00 UTC
Major Cities in ADT
Primary metropolitan centers and financial hubs observing this time zone:
Adoption History & Astronomical Facts
Year Established: 1918
Canada introduced daylight saving across Halifax and coastal rail junctions in 1918 to conserve coal for transatlantic naval convoys. The practice was reaffirmed under federal legislation during the Second World War.
When Atlantic Daylight Time is active, Halifax and Bermuda share the same clock time as Buenos Aires, Argentina, and São Paulo, Brazil, during the Southern Hemisphere winter.
Frequently Asked Questions about ADT
What is the difference between ADT and AST?
Atlantic Daylight Time is one hour ahead of Atlantic Standard Time. During summer, clocks advance by one hour from UTC-4 to UTC-3.
Is ADT the same as Eastern Daylight Time?
No. ADT (UTC-3) is always one hour ahead of EDT (UTC-4). When it is 12:00 noon EDT in New York or Toronto, it is 1:00 PM ADT in Halifax.
Which provinces observe Atlantic Daylight Time?
Nova Scotia, New Brunswick, and Prince Edward Island observe ADT, as well as portions of eastern Quebec, the Magdalen Islands, and coastal communities in southern Labrador.