CDT to AST
+1hCDT
CDTSOURCEAST
ASTGreen rows indicate typical business hours (9 AM - 5 PM)
CDT and AST on the World Map
The map below highlights the CDT (Central Daylight Time) and AST (Atlantic Standard Time) timezone regions across the globe.
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.
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.
Comparing Time Zones: CDT and AST
CDT runs on Central Daylight Time (CDT) at UTC-05:00. AST runs on Atlantic Standard Time (AST) at UTC-04:00. That puts CDT 1 hour ahead of AST — a difference of +1h at the current offsets.
In practice, when it is 9:00 AM in CDT it is 10:00 AM in AST. Midnight in CDT is 1:00 AM in AST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
CDT to AST time conversion table
| CDT (CDT) | AST (AST) | Day |
|---|---|---|
| 12:00 AM | 1:00 AM | same day |
| 6:00 AM | 7:00 AM | same day |
| 7:00 AM | 8:00 AM | same day |
| 8:00 AM | 9:00 AM | same day |
| 9:00 AM | 10:00 AM | same day |
| 12:00 PM | 1:00 PM | same day |
| 3:00 PM | 4:00 PM | same day |
| 5:00 PM | 6:00 PM | same day |
| 6:00 PM | 7:00 PM | same day |
| 9:00 PM | 10:00 PM | same day |
Why people convert CDT to AST time
- Scheduling a call from CDT to AST: a 10:00 AM start in CDT lands at 11:00 AM in AST, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both CDT and AST are inside the 9-to-5 working day between 9:00 AM and 4:00 PM CDT time (10:00 AM–5:00 PM AST). That is roughly 7 hours of usable overlap.
- Coordinating a CDT-based team with AST contacts: quoting times in the other side's local clock — not your own — removes the single biggest source of missed meetings.
- Always state the zone abbreviation, not just the hour. "3:00 PM CDT" is unambiguous; "3 PM" across a +1h gap is not.
- Block 9:00 AM–4:00 PM CDT as the recurring meeting window if you work primarily from CDT and need AST colleagues present.
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.
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.
Best time to call between CDT and AST
Both CDT and AST sit inside the 9 AM – 5 PM working day between 9:00 AM–4:00 PM CDT, which is 10:00 AM–5:00 PM AST. That gives roughly 7 hours of shared time — the safest window for a live call or meeting.
Business hours overlap
CDT and AST share 7 hours of working-hours overlap (9:00 AM–4:00 PM CDT), so scheduling a live meeting is straightforward.
CDT is 1 hour ahead of AST (CDT UTC-05:00 → AST UTC-04:00). The shared working window is 9:00 AM–4:00 PM CDT. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
CDT
☀ Currently in DST
Standard: UTC-06:00 · DST: UTC-05:00
Clocks fall back on Sun, Nov 1, 2026
AST
☀ Currently in DST
Standard: UTC-04:00 · DST: UTC-03:00
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 CDT and AST?
CDT (CDT, UTC-05:00) is 1 hour ahead of AST (AST, UTC-04:00). The gap is currently +1h.
How do I convert CDT time to AST time?
Add +1h to CDT local time. For example, 9:00 AM in CDT is 10:00 AM in AST.
What time is it in AST right now?
AST uses AST at UTC-04:00. Use the live converter at the top of this page — it updates in real time and already accounts for the +1h offset from CDT.
What is the best time to call AST from CDT?
Call between 9:00 AM and 4:00 PM CDT — that maps to 10:00 AM–5:00 PM AST and keeps both parties inside the working day.
Which is ahead, CDT or AST?
CDT is 1 hour ahead of AST. When it is 12:00 PM in CDT it is 1:00 PM in AST.
Does daylight saving time affect the CDT–AST difference?
Neither zone observes daylight saving time, so the +1h offset between CDT and AST is fixed all year.
Which other cities share CDT's time zone?
CDT also covers Chicago, Houston, Dallas, Austin, Winnipeg, Nashville.
Which countries use CDT, CDT's zone?
CDT is used in United States (Central), Canada (Manitoba).
Is there a day difference between CDT and AST?
Not normally. The +1h gap only pushes the date over for late-evening times.
What is the time difference between CDT and AST?
AST is +1h from CDT.
What timezone is CDT in?
CDT operates on its local timezone.
What timezone is AST in?
AST operates on its local timezone.
Which countries use CDT (Central Daylight Time)?
CDT is used in United States (Central), Canada (Manitoba).
Does CDT observe daylight saving time?
Yes, CDT switches to CST during summer months.
What are some interesting facts about CDT?
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.
Which cities are in the AST timezone?
Major cities in the AST timezone include Halifax, San Juan, Santo Domingo, Caracas, La Paz, Fredericton, Charlottetown.
What is the UTC offset for AST?
Atlantic Standard Time (AST) is at UTC-04:00. During daylight saving time, it shifts to ADT.
What should I know about the AST timezone?
Puerto Rico uses AST year-round and does not observe DST. AST is 1 hour ahead of EST.
When is it midnight in CDT, what time is it in AST?
When it is 12:00 AM (midnight) in CDT (CDT), it is +1h later in AST (AST).
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See every conversion from CDT →·See every conversion from AST →