GMT to AST Time Converter

When it is 9:00 AM GMT, it is 5:00 AM AST. Atlantic Standard Time (AST, UTC-4) is 4 hours behind Greenwich Mean Time (GMT, UTC+0). Your working-hours overlap window is 1:00 PM–5:00 PM GMT (9:00 AM–1:00 PM AST).

GMT to AST Conversion Table

Major Cities Using GMT and AST

Greenwich Mean Time (GMT): London, Manchester, Dublin, Edinburgh.

Atlantic Standard Time (AST): Halifax, Saint John, Moncton.

How many hours between GMT and AST?

GMT is UTC+0 and AST is UTC-4, a difference of 4 hours. AST is behind GMT. This difference can shift by an hour in either direction during Daylight Saving Time transitions — if one zone observes DST and the other doesn't, the offset narrows or widens for part of the year.

Business Hours Overlap: GMT ↔ AST

Assuming a 9:00 AM – 5:00 PM workday on each side, your working-hours overlap window is 1:00 pm–5:00 pm gmt (9:00 am–1:00 pm ast). To visualize this instantly for any pair of cities, use the visual meeting planner or the timezone overlap finder — both highlight the green overlap window on a live timeline.

Does GMT observe Daylight Saving Time?

Greenwich Mean Time (GMT) is based on the Europe/London IANA timezone. DST observance depends on the jurisdiction — for example, most of the continental US switches between standard and daylight time, while India, Japan, and most of Southeast Asia do not observe DST at all. WorldClock.lol uses the authoritative IANA timezone database, so every conversion automatically accounts for the correct DST rules on the date you're converting.

When is 9 AM GMT in AST?

When it is 9:00 AM in Greenwich Mean Time (GMT, UTC+0), it is 5:00 AM in Atlantic Standard Time (AST). For other times of day, scan the conversion table above or drop into the interactive converter to pick an exact minute. The converter handles both standard and daylight variants correctly.

How to Use This GMT to AST Converter

1. Type or drag any time in the GMT input above — the AST equivalent updates instantly.
2. Check the day indicator. When the converted time crosses midnight, the tool shows +1 day or −1 day so you don't book a meeting on the wrong date.
3. Copy the shareable URL to send the specific conversion to a colleague — the link preserves your exact selection.
4. Switch directions by swapping the input zones, or open AST to GMT for the reverse.

Related GMT Converters

• GMT to EST
• GMT to PST
• GMT to UTC
• GMT to IST
• GMT to JST
• GMT to CET

Related AST Converters

• EST to AST
• PST to AST
• UTC to AST
• IST to AST
• JST to AST
• CET to AST

More Time Tools

• All Time Zone Converters — browse every supported pair
• About GMT (Greenwich Mean Time) — current time, cities, DST rules
• About AST (Atlantic Standard Time) — current time, cities, DST rules
• Meeting Planner — find the best time for a multi-city meeting
• Best Time to Call — optimal calling windows between any two cities
• UTC Time Now — the reference point for every conversion
• DST Schedule 2026 — every daylight-saving transition this year