AST to GMT
+4hAST
ASTSOURCEGMT
GMTGreen rows indicate typical business hours (9 AM - 5 PM)
AST and GMT on the World Map
The map below highlights the AST (Atlantic Standard Time) and GMT (Greenwich Mean Time) timezone regions across the globe.
AST – Atlantic Standard Time
UTC-04:00Atlantic Standard Time (AST) is the time zone for the Canadian Atlantic provinces and the Caribbean, 4 hours behind UTC.
- •Puerto Rico uses AST year-round and does not observe DST.
- •AST is 1 hour ahead of EST.
- •Halifax, the capital of Nova Scotia, is the largest city in AST Canada.
GMT – Greenwich Mean Time
UTC+00:00Greenwich Mean Time (GMT) is the mean solar time at the Royal Observatory in Greenwich, London. It is the same as UTC+00:00.
- •GMT is based on the Prime Meridian (0° longitude) passing through Greenwich, London.
- •The Royal Observatory in Greenwich has been the reference point for GMT since 1884.
- •GMT and UTC are often used interchangeably, but UTC is based on atomic clocks.
- •Iceland uses GMT year-round and never observes daylight saving time.
- •The UK switches from GMT to BST (British Summer Time) in late March each year.
Understanding the +4h Gap: AST vs GMT
AST runs on Atlantic Standard Time (AST) at UTC-04:00. GMT runs on Greenwich Mean Time (GMT) at UTC+00:00. That puts AST 4 hours ahead of GMT — a difference of +4h at the current offsets.
In practice, when it is 9:00 AM in AST it is 1:00 PM in GMT. Midnight in AST is 4:00 AM in GMT. Neither zone observes daylight saving time, so the offset between them stays constant all year.
AST to GMT time conversion table
| AST (AST) | GMT (GMT) | Day |
|---|---|---|
| 12:00 AM | 4:00 AM | same day |
| 6:00 AM | 10:00 AM | same day |
| 7:00 AM | 11:00 AM | same day |
| 8:00 AM | 12:00 PM | same day |
| 9:00 AM | 1:00 PM | same day |
| 12:00 PM | 4:00 PM | same day |
| 3:00 PM | 7:00 PM | same day |
| 5:00 PM | 9:00 PM | same day |
| 6:00 PM | 10:00 PM | same day |
| 9:00 PM | 1:00 AM | next day |
Why people convert AST to GMT time
- Scheduling a call from AST to GMT: a 10:00 AM start in AST lands at 2:00 PM in GMT, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both AST and GMT are inside the 9-to-5 working day between 9:00 AM and 1:00 PM AST time (1:00 PM–5:00 PM GMT). That is roughly 4 hours of usable overlap.
- Booking travel or deliveries: tracking GMT local time against AST keeps pickup windows and arrival estimates honest across the +4h offset.
- Always state the zone abbreviation, not just the hour. "3:00 PM AST" is unambiguous; "3 PM" across a +4h gap is not.
- Block 9:00 AM–1:00 PM AST as the recurring meeting window if you work primarily from AST and need GMT colleagues present.
About AST (Atlantic Standard Time)
Atlantic Standard Time (AST) covers Canada's Atlantic provinces (Nova Scotia, New Brunswick, Prince Edward Island, and most of Labrador), as well as several Caribbean nations. Puerto Rico and the US Virgin Islands use AST year-round without daylight saving time. The Canadian provinces switch to Atlantic Daylight Time (ADT) in summer.
About GMT (Greenwich Mean Time)
Greenwich Mean Time (GMT) is the clock time at the Royal Observatory in Greenwich, London, which sits on the Prime Meridian (0° longitude). GMT serves as the reference point from which all other time zones are calculated. The United Kingdom uses GMT during winter months and switches to British Summer Time (BST, UTC+01:00) from late March to late October. Several West African nations use GMT year-round. GMT is often used interchangeably with UTC (Coordinated Universal Time), although technically they are different – UTC is based on atomic clocks while GMT is based on Earth's rotation.
Best time to call between AST and GMT
Both AST and GMT sit inside the 9 AM – 5 PM working day between 9:00 AM–1:00 PM AST, which is 1:00 PM–5:00 PM GMT. That gives roughly 4 hours of shared time — the safest window for a live call or meeting.
Business hours overlap
AST and GMT overlap for about 4 hours during the working day — enough for meetings if you avoid the edges of the window.
AST is 4 hours ahead of GMT (AST UTC-04:00 → GMT UTC+00:00). The shared working window is 9:00 AM–1:00 PM AST. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
AST
☀ Currently in DST
Standard: UTC-04:00 · DST: UTC-03:00
Clocks fall back on Sun, Nov 1, 2026
GMT
☀ Currently in DST
Standard: UTC+00:00 · DST: UTC+01:00
Clocks fall back on Sun, Oct 25, 2026
Learn More About Time
Dive deeper into the fascinating world of timekeeping, time zones, and how they shape our global society:
Frequently Asked Questions
What is the time difference between AST and GMT?
AST (AST, UTC-04:00) is 4 hours ahead of GMT (GMT, UTC+00:00). The gap is currently +4h.
How do I convert AST time to GMT time?
Add +4h to AST local time. For example, 9:00 AM in AST is 1:00 PM in GMT.
What time is it in GMT right now?
GMT uses GMT at UTC+00:00. Use the live converter at the top of this page — it updates in real time and already accounts for the +4h offset from AST.
What is the best time to call GMT from AST?
Call between 9:00 AM and 1:00 PM AST — that maps to 1:00 PM–5:00 PM GMT and keeps both parties inside the working day.
Which is ahead, AST or GMT?
AST is 4 hours ahead of GMT. When it is 12:00 PM in AST it is 4:00 PM in GMT.
Does daylight saving time affect the AST–GMT difference?
Neither zone observes daylight saving time, so the +4h offset between AST and GMT is fixed all year.
Which other cities share AST's time zone?
AST also covers Halifax, San Juan, Santo Domingo, Caracas, La Paz, Fredericton, Charlottetown.
Which countries use AST, AST's zone?
AST is used in Canada (Atlantic provinces), Puerto Rico, US Virgin Islands, Dominican Republic, Venezuela, Bolivia, Barbados, Trinidad and Tobago.
Is there a day difference between AST and GMT?
Not normally. The +4h gap only pushes the date over for late-evening times.
What is the time difference between AST and GMT?
GMT is +4h from AST.
What timezone is AST in?
AST operates on its local timezone.
What timezone is GMT in?
GMT operates on its local timezone.
Which countries use AST (Atlantic Standard Time)?
AST is used in Canada (Atlantic provinces), Puerto Rico, US Virgin Islands, Dominican Republic, Venezuela, Bolivia, and 2 more countries.
Does AST observe daylight saving time?
Yes, AST switches to ADT during summer months.
What are some interesting facts about AST?
Puerto Rico uses AST year-round and does not observe DST. AST is 1 hour ahead of EST.
Which cities are in the GMT timezone?
Major cities in the GMT timezone include London, Dublin, Lisbon, Accra, Reykjavik, Edinburgh, Casablanca, Dakar.
What is the UTC offset for GMT?
Greenwich Mean Time (GMT) is at UTC+00:00. During daylight saving time, it shifts to BST.
What should I know about the GMT timezone?
GMT is based on the Prime Meridian (0° longitude) passing through Greenwich, London. The Royal Observatory in Greenwich has been the reference point for GMT since 1884.
When is it midnight in AST, what time is it in GMT?
When it is 12:00 AM (midnight) in AST (AST), it is +4h later in GMT (GMT).
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See every conversion from AST →·See every conversion from GMT →