GMT to AST Time Converter
AST is 4 hours behind GMT. The UK and Ireland are currently on BST (UTC+1:00), and Atlantic Canada and the Caribbean are currently on ADT (UTC-3:00).
Best Time to Call Between GMT and AST
Both zones are inside normal business hours between 1:00 PM and 5:00 PM GMT — that's 9:00 AM to 1:00 PM AST. That's a 4-hour window.
both at work GMT only AST only neither — hours along the strip are GMT.
Common Times Converted
GMT on the left, AST on the right.
GMT to AST: Full 24-Hour Conversion Table
Shaded rows are working hours; the darker shade marks the hours when both zones are at work.
| GMT | AST | Working hours |
|---|---|---|
| 12:00 AM | 8:00 PM prev day | — |
| 1:00 AM | 9:00 PM prev day | — |
| 2:00 AM | 10:00 PM prev day | — |
| 3:00 AM | 11:00 PM prev day | — |
| 4:00 AM | 12:00 AM | — |
| 5:00 AM | 1:00 AM | — |
| 6:00 AM | 2:00 AM | — |
| 7:00 AM | 3:00 AM | — |
| 8:00 AM | 4:00 AM | — |
| 9:00 AM | 5:00 AM | GMT only |
| 10:00 AM | 6:00 AM | GMT only |
| 11:00 AM | 7:00 AM | GMT only |
| 12:00 PM | 8:00 AM | GMT only |
| 1:00 PM | 9:00 AM | Both zones |
| 2:00 PM | 10:00 AM | Both zones |
| 3:00 PM | 11:00 AM | Both zones |
| 4:00 PM | 12:00 PM | Both zones |
| 5:00 PM | 1:00 PM | AST only |
| 6:00 PM | 2:00 PM | AST only |
| 7:00 PM | 3:00 PM | AST only |
| 8:00 PM | 4:00 PM | AST only |
| 9:00 PM | 5:00 PM | — |
| 10:00 PM | 6:00 PM | — |
| 11:00 PM | 7:00 PM | — |
What GMT and AST Actually Are
GMT — Greenwich Mean Time
The UK and Ireland in winter, plus Iceland, Portugal and much of West Africa. Standing at UTC as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, October 25, 2026, to GMT. Often used loosely as a synonym for UTC. They differ by less than a second, so for scheduling they are interchangeable.
Britain ran an experiment from 1968 to 1971 on permanent UTC+1, abandoning GMT entirely. It was scrapped after complaints about dark winter mornings in Scotland.
AST — Atlantic Standard Time
Halifax, San Juan, Santo Domingo, Bermuda. Standing at UTC-4:00 as written, and the region does change its clocks, so its live offset moves by an hour twice a year. The next change is on Sunday, November 1, 2026, to AST. AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.
Atlantic Standard Time is the only North American zone whose name is more commonly associated, worldwide, with a completely different zone — Arabia Standard Time.
What This Means in Practice
Both sides change clocks, on different dates
Both regions observe daylight saving but do not switch on the same day, so for a week or two each spring and fall the gap between them is an hour different from the rest of the year. Those short windows are where recurring invitations quietly break.
Major Cities in Each Zone
Cities on GMT
Cities on AST
Frequently Asked Questions
What is the time difference between GMT and AST?
AST is 4 hours behind GMT.
What is 9:00 AM GMT in AST?
9:00 AM GMT is 5:00 AM AST.
What are the best hours to schedule a call between GMT and AST?
Between 1:00 PM and 5:00 PM GMT, which is 9:00 AM to 1:00 PM AST. Both sides are inside normal business hours through that window.
Does the difference between GMT and AST change during the year?
Yes. Both regions observe daylight saving, and they do not switch on the same dates, so the gap shifts by an hour at least twice a year. The next clock change is on Sunday, October 25, 2026.
Does GMT always mean Greenwich Mean Time?
Often used loosely as a synonym for UTC. They differ by less than a second, so for scheduling they are interchangeable.
Does AST always mean Atlantic Standard Time?
AST also stands for Arabia Standard Time (UTC+3), used in Saudi Arabia, Iraq and Kuwait.