AST — Atlantic Standard Time
AST is UTC-04:00, the winter time in Halifax. In summer, clocks there move to UTC-03:00.
Current time in AST
11:22:15
Atlantic Standard Time · UTC-04:00
About AST
AST is used in Atlantic Canada and parts of the Caribbean. Canada switches to ADT (UTC-3) in summer.
Working with AST
The same offset, UTC-04:00, is also used by EDT, though each follows its own daylight saving rules — or none — so they do not stay aligned all year. One hour to the west of AST in this directory sits EST (UTC-05:00); one hour to the east, BRT (UTC-03:00).
The letters AST are also used for Arabia Standard Time (UTC+03:00). Quote the IANA identifier, America/Halifax, wherever the meaning has to be unambiguous.
Clock changes in AST
AST follows the North American rule: clocks go forward on the second Sunday in March and back on the first Sunday in November, at 02:00 local time.
| Date | Change | New offset |
|---|---|---|
| March 14, 2027 | Clocks go forward one hour on Mar 14, 2027 at 02:00, moving from UTC-04:00 to UTC-03:00. | UTC-03:00 |
| November 7, 2027 | Clocks go back one hour on Nov 7, 2027 at 02:00, moving from UTC-03:00 to UTC-04:00. | UTC-04:00 |
Clock history of America/Halifax
| Period | Clocks set to | Seasonal changes |
|---|---|---|
| since 1945 | UTC-04:00 | 77 years with a change, 1946–2026 |
| 1942–1945 | UTC-03:00 | none |
| 1902–1942 | UTC-04:00 | 24 years with a change, 1916–1941 |
| 1900–1902 | UTC-04:14:24 | none |
Who keeps UTC-04:00
All year: Caracas. Part of the year: New York, Toronto, Havana, Montreal, Washington, D.C., Boston, Atlanta and Miami from March 14, 2027 to November 7, 2027; Santiago from April 4, 2027 to September 5, 2027.
Countries and territories that keep UTC-04:00 all year, from every entry in the tz database: Anguilla, Antigua & Barbuda, Aruba, Barbados, Bolivia, parts of Brazil, British Virgin Islands, parts of Canada, Caribbean Netherlands, Curaçao, Dominica, the Dominican Republic, Grenada, Guadeloupe, Guyana, Martinique, Montserrat, Puerto Rico, Sint Maarten, St. Barthélemy, St. Kitts & Nevis, St. Lucia, St. Martin, St. Vincent & Grenadines and 3 more. For part of the year: the Bahamas, Bermuda, parts of Canada, parts of Chile, Cuba, parts of Greenland, Haiti, Turks & Caicos Islands and parts of the United States. Where it is kept all year, UTC-04:00 also goes by these names in the tz database: Amazon Standard Time, Bolivia Time, Guyana Time and Venezuela Time.
Where AST stands today
AST is in force in America/Halifax now, at UTC-04:00. On March 14, 2027, 132 days from the day this page was generated, clocks there move to UTC-03:00, and AST stops applying there until the following change. A time written as AST always means UTC-04:00, so anything scheduled across that date should name the place, not just the letters.
America/Halifax is on standard time at the moment; the summer offset applies for part of the year and is listed above.
A working day on AST
| Place | AST’s 09:00–17:00 there | Over the next 12 months |
|---|---|---|
| UTC | 13:00–21:00 | — |
| New York | 08:00–16:00 / 09:00–17:00 | 7 h to 8 h |
| London | 13:00–21:00 / 14:00–22:00 | 3 h to 4 h |
| Tokyo | 22:00–06:00 | none all year |
At 09:00 on a Monday on AST time, every city in this directory has already reached Monday. By 17:00 on a Friday on AST time, New Delhi, Shanghai, Beijing, Mumbai, Shenzhen, Karachi and 44 more have already reached Saturday. For part of the year, so have Cairo, Kyiv, Bucharest, Jerusalem, Athens, Helsinki and 1 more.
How AST compares with other zones
Right now AST runs ahead of New York and Los Angeles and behind UTC, London, Berlin, Dubai, Kolkata, Singapore, Tokyo and Sydney.
| Zone | UTC offset | Difference from AST | Over the next 12 months |
|---|---|---|---|
| UTC | UTC+00:00 | 4h behind | all year |
| New York | UTC-05:00 | 1h ahead | 1h ahead / Same time |
| London | UTC+00:00 | 4h behind | 4h behind / 5h behind |
| Berlin | UTC+01:00 | 5h behind | 5h behind / 6h behind |
| Dubai | UTC+04:00 | 8h behind | all year |
| Kolkata | UTC+05:30 | 9h 30m behind | all year |
| Singapore | UTC+08:00 | 12h behind | all year |
| Tokyo | UTC+09:00 | 13h behind | all year |
| Sydney | UTC+11:00 | 15h behind | 14h behind / 15h behind |
| Los Angeles | UTC-08:00 | 4h ahead | 4h ahead / 3h ahead |
Cities using AST
- Halifax
Convert AST to another zone
Related time zones
Time zone rules: IANA tz database release 2026c, applied when this page was generated on 2026-11-02.
Frequently asked questions
What is AST?
Atlantic Standard Time, AST, is UTC-04:00. AST is used in Atlantic Canada and parts of the Caribbean. Canada switches to ADT (UTC-3) in summer.
Does AST change for daylight saving?
AST itself never changes: it always means UTC-04:00. America/Halifax moves between UTC-04:00 in winter and UTC-03:00 in summer, so a time labelled AST only matches the local clock there for part of the year.
What time is it on AST when it is 09:00 in London?
05:00 until March 28, 2027 and from October 31, 2027; 04:00 from March 28, 2027 to October 31, 2027.
Is AST the same as EDT?
As labels, both mean UTC-04:00. The places behind them, Halifax and New York, do not keep the same clock for a whole day at any point in the coming year.