AST to CDT Converter
Convert time between Atlantic Standard Time (AST) and Central Daylight Time (CDT)
Atlantic Standard Time (AST)
Central Daylight Time (CDT)
Time Difference
Central Daylight Time (CDT) is 0 hours ahead of Atlantic Standard Time (AST)
Select Date
Select Time
Quick Reference
| AST | CDT |
|---|---|
| 22:00 | 20:00 |
| 00:00 | 22:00 |
| 02:00 | 00:00 |
| 04:00 | 02:00 |
| 06:00 | 04:00 |
| 08:00 | 06:00 |
| 10:00 | 08:00 |
| 12:00 | 10:00 |
| 14:00 | 12:00 |
| 16:00 | 14:00 |
| 18:00 | 16:00 |
| 20:00 | 18:00 |
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 AST to CDT Time Conversion
Converting time between Atlantic Standard Time (AST) and Central Daylight Time (CDT) is unique because it represents the smallest time difference (just 1 hour) available for Atlantic-US region coordination. AST is UTC-4 and is only active from the first Sunday in November through the second Sunday in March (winter months). CDT is UTC-5 and is active from the second Sunday in March through the first Sunday in November (summer months). When both are active simultaneously, AST is only 1 hour ahead of CDT.
This conversion is most relevant during the summer months (March-November) when Atlantic Canada observes Atlantic Daylight Time (ADT, UTC-3) but is technically still on AST according to standard notation. In practice, when Atlantic switches to ADT, the difference becomes truly minimal (technically ADT-CDT is only 2 hours, but the user typically thinks of their current time as AST). This makes Atlantic-Central coordination during summer months nearly seamless, requiring minimal time zone mental calculations. After November, both regions transition to standard time (AST and CST), creating a 2-hour difference.
Common Use Cases for AST to CDT Conversion
Business & Work
- Scheduling summer meetings between Atlantic Canada and Central region offices
- Coordinating software development teams during peak summer collaboration season
- Managing business operations with Central region partners during daylight months
- Planning conference calls and project deadlines during high-engagement periods
Personal & Travel
- Coordinating with family and friends in the Central region during summer
- Planning summer travel from Atlantic Canada to Central destinations
- Scheduling virtual meetings with Central region relatives during vacation season
- Arranging online collaboration with Central region-based colleagues in summer
Time Zone Information
Atlantic Standard Time (AST)
- UTC Offset: UTC-4 (Winter only, November-March)
- IANA Timezone: America/Halifax
- Daylight Saving: Transitions to ADT (UTC-3) on second Sunday in March
- Major Cities: Halifax, Saint John, Charlottetown, Fredericton
- Coverage: Atlantic Canada (Nova Scotia, New Brunswick, Prince Edward Island)
Central Daylight Time (CDT)
- UTC Offset: UTC-5 (Summer only, March-November)
- IANA Timezone: America/Chicago
- Daylight Saving: Active March to November. Transitions from CST (UTC-6) on second Sunday in March
- Major Cities: Chicago, Dallas, Houston, Kansas City, St. Louis
- Coverage: Central United States and Canada (summer months)
Quick Reference: AST to CDT
Remember: AST is 1 hour ahead of CDT during the March-November period when both daylight times are active. Outside these months, the conversion changes to AST-CST with a 2-hour difference. This conversion offers the minimal time difference for Atlantic-US coordination.
Frequently Asked Questions
What is the time difference between AST and CDT?
Atlantic Standard Time (AST) is UTC-4, while Central Daylight Time (CDT) is UTC-5. This means AST is 1 hour ahead of CDT. When it's 12:00 PM (noon) in Halifax (AST), it's 11:00 AM in Chicago (CDT). Note: This 1-hour difference occurs during spring and summer months (March to November) when Atlantic Daylight Time (ADT, UTC-3) is active. From November to March, Atlantic is on AST while Central is on CST, creating a 2-hour difference.
How does the AST to CDT offset differ from other Atlantic-US conversions?
The 1-hour offset between AST and CDT is the absolute smallest time difference for Atlantic-US region conversions, making it exceptionally favorable for business coordination. AST-to-CDT only applies during the specific period when Atlantic Daylight Time (ADT, UTC-3) is active and Central Daylight Time (CDT, UTC-5) is active simultaneously. This makes Atlantic-Central coordination during summer months nearly seamless. Outside the March-November window, the difference becomes 2 hours (AST-CST). The minimal offset maximizes business hour overlap.
Does Atlantic Canada observe daylight saving time like Central region?
Yes, Atlantic Canada transitions to Atlantic Daylight Time (ADT, UTC-3) on the second Sunday in March and returns to Atlantic Standard Time (AST, UTC-4) on the first Sunday in November. During this period, the Central region is on Central Daylight Time (CDT, UTC-5). Both regions use the same transition dates (second Sunday in March and first Sunday in November). This means from March to November, the difference is 1 hour (ADT to CDT). From November to March, it becomes 2 hours (AST to CST).
When is AST to CDT conversion most relevant, and when does it change?
AST to CDT conversion is most relevant from mid-March through early November when both Atlantic Daylight Time and Central Daylight Time are active simultaneously. The conversion is relevant on the second Sunday in March (when Atlantic transitions to ADT) through the first Sunday in November (when both regions transition back to standard time). Before mid-March, you need AST-to-CST conversion (2-hour difference). After early November, you again need AST-to-CST conversion. The 1-hour window provides the smoothest coordination period.
What are the best times to schedule calls between Atlantic Canada and Central region during summer months?
With only a 1-hour difference, business hour overlap is exceptional. Atlantic morning (8 AM-12 PM ADT) overlaps with Central morning (7 AM-11 AM CDT), providing substantial morning availability. Afternoon calls work equally well: 2 PM-5 PM CDT (3 PM-6 PM ADT) aligns perfectly with late afternoon in Atlantic and mid-afternoon in Central. The 9 AM-11 AM ADT window (8 AM-10 AM CDT) is particularly ideal, catching both regions during peak morning productivity. Almost any standard business hour works well.
Why is the Central region optimal for Atlantic Canada coordination during summer?
During summer months (March-November), the Central region offers unbeatable coordination advantages: the minimal 1-hour time difference, major business hubs in Chicago, Dallas, Houston, and other significant cities, significant corporate headquarters and tech presence, and excellent flight connectivity from Atlantic Canada. The nearly-aligned time zones mean you can schedule meetings during standard business hours in both regions without complex calculations. Many companies specifically choose Central region partnerships to maximize real-time collaboration with Atlantic Canada. Combined with the region's economic importance, it's the premier choice.
Pro Tips
- • AST to CDT is only relevant during March-November when both daylight times are active. Outside these months, the conversion is AST-CST with a 2-hour difference.
- • Both regions transition on the same dates: second Sunday in March and first Sunday in November. Only one calendar adjustment needed per year for AST-CDT coordination.
- • With just 1 hour difference during summer, almost any standard business hour works. Schedule 8 AM-5 PM AST meetings with 7 AM-4 PM CDT colleagues with minimal conflict.
- • The 9-11 AM ADT window (8-10 AM CDT) is peak productivity time in both regions. Use this slot for important meetings requiring full attention from both teams.
- • During summer months, time zone conversion is almost trivial. Use this period for maximum real-time collaboration before winter coordination becomes more complex.
- • Mark transition dates carefully: second Sunday in March (AST→ADT, creating 1-hour difference) and first Sunday in November (ADT→AST, creating 2-hour difference).
Update Logs
View the latest updates and features