AST to GMT: AST is 3 hours behind GMT
Atlantic Time is 3 hours behind Greenwich Mean Time right now. It is 12:21 am ADT in Atlantic and 3:21 am GMT in GMT.
Convert a specific time from AST to GMT
Pick any time and date to convert it both ways. The conversion runs in your browser against the real zone rules, so a date inside a daylight saving period gets that period's offset rather than today's.
What is the time difference between AST and GMT?
Greenwich Mean Time is 3 hours ahead of Atlantic Time. To go from AST to GMT you add 3 hours. That gap is not fixed. Across 2026 the distance between these two zones takes 2 different values, from 3 hours to 4 hours, because Atlantic moves its clocks and GMT does not. This page recomputes it rather than assuming.
AST to GMT conversion table
Every hour of Friday, September 25, 2026 in Atlantic, with the matching reading in GMT. 3 of the 24 hours land on a different calendar date in GMT, which is the part people get wrong when they schedule across this pair.
| AST | AST 24h | GMT | GMT 24h | Date |
|---|---|---|---|---|
| 12:00 am | 00:00 | 3:00 am | 03:00 | same day |
| 1:00 am | 01:00 | 4:00 am | 04:00 | same day |
| 2:00 am | 02:00 | 5:00 am | 05:00 | same day |
| 3:00 am | 03:00 | 6:00 am | 06:00 | same day |
| 4:00 am | 04:00 | 7:00 am | 07:00 | same day |
| 5:00 am | 05:00 | 8:00 am | 08:00 | same day |
| 6:00 am | 06:00 | 9:00 am | 09:00 | same day |
| 7:00 am | 07:00 | 10:00 am | 10:00 | same day |
| 8:00 am | 08:00 | 11:00 am | 11:00 | same day |
| 9:00 am | 09:00 | 12:00 pm | 12:00 | same day |
| 10:00 am | 10:00 | 1:00 pm | 13:00 | same day |
| 11:00 am | 11:00 | 2:00 pm | 14:00 | same day |
| 12:00 pm | 12:00 | 3:00 pm | 15:00 | same day |
| 1:00 pm | 13:00 | 4:00 pm | 16:00 | same day |
| 2:00 pm | 14:00 | 5:00 pm | 17:00 | same day |
| 3:00 pm | 15:00 | 6:00 pm | 18:00 | same day |
| 4:00 pm | 16:00 | 7:00 pm | 19:00 | same day |
| 5:00 pm | 17:00 | 8:00 pm | 20:00 | same day |
| 6:00 pm | 18:00 | 9:00 pm | 21:00 | same day |
| 7:00 pm | 19:00 | 10:00 pm | 22:00 | same day |
| 8:00 pm | 20:00 | 11:00 pm | 23:00 | same day |
| 9:00 pm | 21:00 | 12:00 am | 00:00 | the next day |
| 10:00 pm | 22:00 | 1:00 am | 01:00 | the next day |
| 11:00 pm | 23:00 | 2:00 am | 02:00 | the next day |
What are the best hours to schedule a call between AST and GMT?
5 hours of the standard 9:00 am to 5:00 pm working day line up in both zones, from 9:00 am AST to 2:00 pm AST. In GMT that window reads 12:00 pm to 5:00 pm. Outside it, one side is either not yet at their desk or already gone.
| AST | GMT | Working hours | Note |
|---|---|---|---|
| 9:00 am | 12:00 pm | both sides | mid morning in Atlantic, noon in GMT |
| 10:00 am | 1:00 pm | both sides | mid morning in Atlantic, afternoon in GMT |
| 11:00 am | 2:00 pm | both sides | mid morning in Atlantic, afternoon in GMT |
| 12:00 pm | 3:00 pm | both sides | noon in Atlantic, afternoon in GMT |
| 1:00 pm | 4:00 pm | both sides | afternoon in Atlantic, afternoon in GMT |
Does daylight saving change AST to GMT?
Atlantic Time is currently on ADT and changes next on Sunday, November 1, 2026, when the clock falls back from 1:59 am to 1:00 am and the offset moves from UTC-3 to UTC-4.
Greenwich Mean Time does not move its clocks at all, so its UTC+0 offset holds every day of the year.
Because the two sides do not move together, the answer to this conversion changes during the year. For part of the year the gap is 3 hours and for the rest it is 4 hours. The table above is built for today, not for an average day.
Is AST ahead of or behind GMT?
AST is behind GMT by 3 hours: when it is 12:00 pm in Atlantic, it is 3:00 pm in GMT. One wrinkle worth knowing: AST and ADT are two names for the same zone, not two zones. Atlantic Time reads AST in winter and ADT in summer. When somebody types "ast to gmt" they nearly always mean the zone rather than the literal winter offset, so this page resolves AST to America/Halifax and GMT to Etc/GMT and applies whichever offset is genuinely in force on the day.
Atlantic Time covers Halifax, Moncton and the Canadian Maritimes. Greenwich Mean Time covers identical to UTC as a clock reading, and a separate thing as a standard. The identifiers behind them are America/Halifax and Etc/GMT, which is what any calendar or scheduling system should be storing rather than a fixed number of hours.
Questions
- What is AST in GMT?
- AST is 3 hours behind GMT. 9:00 am AST is 12:00 pm GMT.
- How many hours ahead is GMT of AST?
- GMT is 3 hours ahead of AST. That varies across the year, between 3 hours and 4 hours.
- What time is it in GMT right now?
- 3:21 am GMT on Friday, September 25, 2026.
- When can Atlantic and GMT meet during working hours?
- Between 9:00 am and 2:00 pm AST, which is 12:00 pm to 5:00 pm GMT.
- Does this account for daylight saving?
- Yes. Every reading is computed from the IANA database for the actual date, so ADT and GMT are the abbreviations genuinely in force today rather than a fixed assumption.
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