GMT to AST: GMT is 3 hours ahead of AST
Greenwich Mean Time is 3 hours ahead of Atlantic Time right now. It is 3:21 am GMT in GMT and 12:21 am ADT in Atlantic.
Convert a specific time from GMT to AST
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 GMT and AST?
Atlantic Time is 3 hours behind Greenwich Mean Time. To go from GMT to AST you subtract 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.
GMT to AST conversion table
Every hour of Friday, September 25, 2026 in GMT, with the matching reading in Atlantic. 3 of the 24 hours land on a different calendar date in Atlantic, which is the part people get wrong when they schedule across this pair.
| GMT | GMT 24h | AST | AST 24h | Date |
|---|---|---|---|---|
| 12:00 am | 00:00 | 9:00 pm | 21:00 | the previous day |
| 1:00 am | 01:00 | 10:00 pm | 22:00 | the previous day |
| 2:00 am | 02:00 | 11:00 pm | 23:00 | the previous day |
| 3:00 am | 03:00 | 12:00 am | 00:00 | same day |
| 4:00 am | 04:00 | 1:00 am | 01:00 | same day |
| 5:00 am | 05:00 | 2:00 am | 02:00 | same day |
| 6:00 am | 06:00 | 3:00 am | 03:00 | same day |
| 7:00 am | 07:00 | 4:00 am | 04:00 | same day |
| 8:00 am | 08:00 | 5:00 am | 05:00 | same day |
| 9:00 am | 09:00 | 6:00 am | 06:00 | same day |
| 10:00 am | 10:00 | 7:00 am | 07:00 | same day |
| 11:00 am | 11:00 | 8:00 am | 08:00 | same day |
| 12:00 pm | 12:00 | 9:00 am | 09:00 | same day |
| 1:00 pm | 13:00 | 10:00 am | 10:00 | same day |
| 2:00 pm | 14:00 | 11:00 am | 11:00 | same day |
| 3:00 pm | 15:00 | 12:00 pm | 12:00 | same day |
| 4:00 pm | 16:00 | 1:00 pm | 13:00 | same day |
| 5:00 pm | 17:00 | 2:00 pm | 14:00 | same day |
| 6:00 pm | 18:00 | 3:00 pm | 15:00 | same day |
| 7:00 pm | 19:00 | 4:00 pm | 16:00 | same day |
| 8:00 pm | 20:00 | 5:00 pm | 17:00 | same day |
| 9:00 pm | 21:00 | 6:00 pm | 18:00 | same day |
| 10:00 pm | 22:00 | 7:00 pm | 19:00 | same day |
| 11:00 pm | 23:00 | 8:00 pm | 20:00 | same day |
What are the best hours to schedule a call between GMT and AST?
5 hours of the standard 9:00 am to 5:00 pm working day line up in both zones, from 12:00 pm GMT to 5:00 pm GMT. In Atlantic that window reads 9:00 am to 2:00 pm. Outside it, one side is either not yet at their desk or already gone.
| GMT | AST | Working hours | Note |
|---|---|---|---|
| 12:00 pm | 9:00 am | both sides | noon in GMT, mid morning in Atlantic |
| 1:00 pm | 10:00 am | both sides | afternoon in GMT, mid morning in Atlantic |
| 2:00 pm | 11:00 am | both sides | afternoon in GMT, mid morning in Atlantic |
| 3:00 pm | 12:00 pm | both sides | afternoon in GMT, noon in Atlantic |
| 4:00 pm | 1:00 pm | both sides | afternoon in GMT, afternoon in Atlantic |
Does daylight saving change GMT to AST?
Greenwich Mean Time does not move its clocks at all, so its UTC+0 offset holds every day of the year.
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.
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 GMT ahead of or behind AST?
GMT is ahead of AST by 3 hours: when it is 12:00 pm in GMT, it is 9:00 am in Atlantic. 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 "gmt to ast" they nearly always mean the zone rather than the literal winter offset, so this page resolves GMT to Etc/GMT and AST to America/Halifax and applies whichever offset is genuinely in force on the day.
Greenwich Mean Time covers identical to UTC as a clock reading, and a separate thing as a standard. Atlantic Time covers Halifax, Moncton and the Canadian Maritimes. The identifiers behind them are Etc/GMT and America/Halifax, which is what any calendar or scheduling system should be storing rather than a fixed number of hours.
Questions
- What is GMT in AST?
- GMT is 3 hours ahead of AST. 9:00 am GMT is 6:00 am AST.
- How many hours ahead is AST of GMT?
- AST is 3 hours behind GMT. That varies across the year, between 3 hours and 4 hours.
- What time is it in Atlantic right now?
- 12:21 am ADT on Friday, September 25, 2026.
- When can GMT and Atlantic meet during working hours?
- Between 12:00 pm and 5:00 pm GMT, which is 9:00 am to 2:00 pm AST.
- Does this account for daylight saving?
- Yes. Every reading is computed from the IANA database for the actual date, so GMT and ADT are the abbreviations genuinely in force today rather than a fixed assumption.
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