AST to CDT
-1hAST
ASTSOURCECDT
CDTGreen rows indicate typical business hours (9 AM - 5 PM)
AST and CDT on the World Map
The map below highlights the AST (Atlantic Standard Time) and CDT (Central Daylight 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.
CDT – Central Daylight Time
UTC-05:00Central Daylight Time (CDT) is the daylight saving offset in the Central Time Zone, 5 hours behind UTC.
- •CDT is the same offset as EST (UTC-05:00), which can cause confusion.
- •CDT runs from the second Sunday in March to the first Sunday in November.
Everything You Need to Know About AST and CDT Time
AST runs on Atlantic Standard Time (AST) at UTC-04:00. CDT runs on Central Daylight Time (CDT) at UTC-05:00. That puts AST 1 hour behind CDT — a difference of -1h at the current offsets.
In practice, when it is 9:00 AM in AST it is 8:00 AM in CDT. Midnight in AST is 11:00 PM in CDT. Neither zone observes daylight saving time, so the offset between them stays constant all year.
AST to CDT time conversion table
| AST (AST) | CDT (CDT) | Day |
|---|---|---|
| 12:00 AM | 11:00 PM | previous day |
| 6:00 AM | 5:00 AM | same day |
| 7:00 AM | 6:00 AM | same day |
| 8:00 AM | 7:00 AM | same day |
| 9:00 AM | 8:00 AM | same day |
| 12:00 PM | 11:00 AM | same day |
| 3:00 PM | 2:00 PM | same day |
| 5:00 PM | 4:00 PM | same day |
| 6:00 PM | 5:00 PM | same day |
| 9:00 PM | 8:00 PM | same day |
Why people convert AST to CDT time
- Scheduling a call from AST to CDT: a 10:00 AM start in AST lands at 9:00 AM in CDT, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both AST and CDT are inside the 9-to-5 working day between 10:00 AM and 5:00 PM AST time (9:00 AM–4:00 PM CDT). That is roughly 7 hours of usable overlap.
- Booking travel or deliveries: tracking CDT local time against AST keeps pickup windows and arrival estimates honest across the -1h offset.
- Always state the zone abbreviation, not just the hour. "3:00 PM AST" is unambiguous; "3 PM" across a -1h gap is not.
- Block 10:00 AM–5:00 PM AST as the recurring meeting window if you work primarily from AST and need CDT 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 CDT (Central Daylight Time)
Central Daylight Time (CDT) is observed during summer months in the US and Canadian portions of the Central Time Zone. Clocks are moved forward by one hour, aligning with Eastern Standard Time (EST). Most of Mexico and Central America do not observe CDT, staying on CST year-round.
Best time to call between AST and CDT
Both AST and CDT sit inside the 9 AM – 5 PM working day between 10:00 AM–5:00 PM AST, which is 9:00 AM–4:00 PM CDT. That gives roughly 7 hours of shared time — the safest window for a live call or meeting.
Business hours overlap
AST and CDT share 7 hours of working-hours overlap (10:00 AM–5:00 PM AST), so scheduling a live meeting is straightforward.
AST is 1 hour behind CDT (AST UTC-04:00 → CDT UTC-05:00). The shared working window is 10:00 AM–5:00 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
CDT
☀ Currently in DST
Standard: UTC-06:00 · DST: UTC-05:00
Clocks fall back on Sun, Nov 1, 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 CDT?
AST (AST, UTC-04:00) is 1 hour behind CDT (CDT, UTC-05:00). The gap is currently -1h.
How do I convert AST time to CDT time?
Add -1h to AST local time. For example, 9:00 AM in AST is 8:00 AM in CDT.
What time is it in CDT right now?
CDT uses CDT at UTC-05:00. Use the live converter at the top of this page — it updates in real time and already accounts for the -1h offset from AST.
What is the best time to call CDT from AST?
Call between 10:00 AM and 5:00 PM AST — that maps to 9:00 AM–4:00 PM CDT and keeps both parties inside the working day.
Which is behind, AST or CDT?
AST is 1 hour behind CDT. When it is 12:00 PM in AST it is 11:00 AM in CDT.
Does daylight saving time affect the AST–CDT difference?
Neither zone observes daylight saving time, so the -1h offset between AST and CDT 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 CDT?
Not normally. The -1h gap only pushes the date over the previous day.
What is the time difference between AST and CDT?
CDT is -1h from AST.
What timezone is AST in?
AST operates on its local timezone.
What timezone is CDT in?
CDT 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 CDT timezone?
Major cities in the CDT timezone include Chicago, Houston, Dallas, Austin, Winnipeg, Nashville.
What is the UTC offset for CDT?
Central Daylight Time (CDT) is at UTC-05:00. During daylight saving time, it shifts to CST.
What should I know about the CDT timezone?
CDT is the same offset as EST (UTC-05:00), which can cause confusion. CDT runs from the second Sunday in March to the first Sunday in November.
When is it midnight in AST, what time is it in CDT?
When it is 12:00 AM (midnight) in AST (AST), it is -1h later in CDT (CDT).
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See every conversion from AST →·See every conversion from CDT →