CDT to AST Converter
Convert time between Central Daylight Time (CDT) and Atlantic Standard Time (AST)
Central Daylight Time (CDT)
Atlantic Standard Time (AST)
Time Difference
Atlantic Standard Time (AST) is 0 hours ahead of Central Daylight Time (CDT)
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Select Time
Quick Reference
| CDT | AST |
|---|---|
| 20:00 | 22:00 |
| 22:00 | 00:00 |
| 00:00 | 02:00 |
| 02:00 | 04:00 |
| 04:00 | 06:00 |
| 06:00 | 08:00 |
| 08:00 | 10:00 |
| 10:00 | 12:00 |
| 12:00 | 14:00 |
| 14:00 | 16:00 |
| 16:00 | 18:00 |
| 18:00 | 20:00 |
Top 10 Most Common Time Zones
| Abbreviation | Full Name | UTC Offset | Typical Use |
|---|---|---|---|
| UTC | Coordinated Universal Time | UTC ±0 | Global reference standard (servers, logs, APIs) |
| EST / EDT | Eastern (US) Time | UTC −5 / −4 | New York, Toronto — North American business hub |
| CST / CDT | Central (US) Time | UTC −6 / −5 | Chicago, Dallas — US central business region |
| PST / PDT | Pacific (US) Time | UTC −8 / −7 | San Francisco, Los Angeles — tech industry standard |
| GMT / BST | Greenwich Mean / British Summer Time | UTC 0 / +1 | UK, used globally as a reference with UTC |
| CET / CEST | Central European (Summer) Time | UTC +1 / +2 | Paris, Berlin, Amsterdam — EU business core |
| IST | India Standard Time | UTC +5:30 | India — major IT & outsourcing region |
| CST | China Standard Time | UTC +8 | Beijing, Shanghai — East Asia business hub |
| JST | Japan Standard Time | UTC +9 | Tokyo — finance & tech hub |
| AEST / AEDT | Australian Eastern (Daylight) Time | UTC +10 / +11 | Sydney, Melbourne — APAC regional business |
Why Time Zone Abbreviations Are Ambiguous
Unlike standardized identifiers (like America/New_York or Europe/London from the IANA tz database), abbreviations such as "CST" or "IST" are not globally unique. They can refer to different time zones depending on context — country, region, or even time of year (due to daylight saving time).
Common Ambiguous Time Zone Abbreviations
| Abbrev. | Common Meaning(s) | UTC Offset | Region(s) |
|---|---|---|---|
| CST | Central Standard Time / China Standard Time / Cuba Standard Time | UTC−6 / UTC+8 / UTC−5 | North America, China, Cuba |
| IST | Indian Standard Time / Irish Standard Time / Israel Standard Time | UTC+5:30 / UTC+1 / UTC+2 | India, Ireland, Israel |
| AST | Atlantic Standard Time / Arabia Standard Time | UTC−4 / UTC+3 | Caribbean, Canada, Middle East |
| PST | Pacific Standard Time / Philippine Standard Time | UTC−8 / UTC+8 | North America, Philippines |
| EST | Eastern Standard Time (North America / Australia) | UTC−5 / UTC+10 | North America, Australia |
✅ Best Practice
To avoid ambiguity, always:
- Use IANA tz identifiers — e.g.,
America/New_Yorkinstead of "EST" - Specify UTC offset explicitly — e.g.,
UTC−5when abbreviations must be used - Include the full timezone name — e.g., "Eastern Standard Time (EST)" with UTC offset
Related Time Zone Conversions
About CDT to AST Time Conversion
Central Daylight Time (CDT) is UTC-5 (used during daylight saving time from March to November) and is observed across the central United States and parts of Canada and Mexico. Atlantic Standard Time (AST) is UTC-4 and is used in Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island, and parts of Newfoundland and Labrador) as well as some Caribbean islands. AST is 1 hour ahead of CDT during the CDT period.
This conversion is essential for business coordination between central North America and Atlantic Canada, as well as for travel planning and communication across these regions. Understanding the time difference helps ensure accurate scheduling for business meetings, family calls, and coordinated activities. Note that while CDT observes daylight saving, AST does not, creating a dynamic 1-hour difference.
Common Use Cases for CDT to AST Conversion
Business & Work
- Scheduling meetings between central US offices and Atlantic Canada operations
- Coordinating with Atlantic Canada business partners and clients
- Planning conference calls across the Central and Atlantic time zones
- Managing cross-border business operations
Personal & Travel
- Coordinating with family and friends in Atlantic Canada
- Planning travel to Nova Scotia, New Brunswick, or Prince Edward Island
- Scheduling events that include participants from both regions
- Understanding time differences for communications
Time Zone Information
Central Daylight Time (CDT)
- UTC Offset: UTC-5
- IANA Timezone: America/Chicago
- Daylight Saving: Second Sunday in March to First Sunday in November
- Major Cities: Chicago, Dallas, Houston, Austin, Memphis
- Coverage: Central United States and parts of Canada
Atlantic Standard Time (AST)
- UTC Offset: UTC-4 (UTC-3 during ADT)
- IANA Timezone: America/Halifax
- Daylight Saving: Second Sunday in March to First Sunday in November
- Major Cities: Halifax, Saint John, Charlottetown, St. John's
- Coverage: Atlantic Canada and some Caribbean islands
Quick Reference: CDT to AST
Note: AST is always 1 hour ahead of CDT (March - November)
Frequently Asked Questions
What is the time difference between CDT and AST?
Central Daylight Time (CDT) is UTC-5, while Atlantic Standard Time (AST) is UTC-4. This means AST is 1 hour ahead of CDT. When you have 8:00 AM in Chicago (CDT), it's 9:00 AM in Halifax (AST).
Why is AST only 1 hour ahead despite the geographic distance?
AST is Atlantic Standard Time used in Canada's Atlantic provinces. While the geographic distance between Chicago and Halifax is significant, the time zone difference is only 1 hour because AST is UTC-4, positioned between the Central (UTC-5) and Eastern (UTC-3) zones. Atlantic Canada is positioned to the east, hence one hour ahead.
Does AST observe daylight saving time like CDT?
No, Atlantic Standard Time (AST) does not observe daylight saving time. It remains UTC-4 throughout the year. This means that when CDT changes to CST in November, the time difference changes from 1 hour to 2 hours. CDT is only 1 hour ahead of AST from March to November.
What are the best times to schedule calls between Central and Atlantic regions?
Business hour overlap is good during the CDT period. Morning meetings (9-11 AM CDT) correspond to 10 AM-12 PM AST. Afternoon meetings (2-4 PM CDT) correspond to 3-5 PM AST. These windows provide good overlap for both business hours and personal availability.
Why is CDT to AST conversion important for business?
Central US and Atlantic Canada have significant business connections. Many Canadian companies headquartered or operating in Halifax, Saint John, and other Atlantic centers work with central US businesses in Chicago, Dallas, and Houston. This includes technology, maritime, energy, and trade operations requiring regular coordination.
Do all Atlantic Canada provinces observe the same time?
Most Atlantic provinces use AST (UTC-4) year-round. However, Newfoundland and Labrador observe Newfoundland Standard Time (NST, UTC-3:30), which is 30 minutes different. This unique 30-minute offset can affect scheduling for St. John's and other Newfoundland locations.
Pro Tips
- • CDT to AST is only 1 hour during daylight saving months (March-November). From November to March, it becomes 2 hours when CDT switches to CST.
- • AST does not observe daylight saving time, making it a static time zone. This simplifies long-term scheduling but requires attention during seasonal transitions.
- • Schedule morning calls (9-10 AM CDT) for 10-11 AM AST to catch both regions at the start of the workday.
- • Atlantic Canada has unique business advantages: strategic location for North Atlantic trade, strong tech presence, and marine industry operations.
- • Use the 2-3 PM CDT window (3-4 PM AST) for important meetings between Central and Atlantic regions.
- • Always verify if you're scheduling with Newfoundland, as it observes NST (UTC-3:30), which is 30 minutes ahead of AST.
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