IST to AST Converter
Convert time between India Standard Time (IST) and Atlantic Standard Time (AST)
India Standard Time (IST)
Atlantic Standard Time (AST)
Time Difference
Atlantic Standard Time (AST) is 0 hours ahead of India Standard Time (IST)
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Select Time
Quick Reference
| IST | AST |
|---|---|
| 07:30 | 22:00 |
| 09:30 | 00:00 |
| 11:30 | 02:00 |
| 13:30 | 04:00 |
| 15:30 | 06:00 |
| 17:30 | 08:00 |
| 19:30 | 10:00 |
| 21:30 | 12:00 |
| 23:30 | 14:00 |
| 01:30 | 16:00 |
| 03:30 | 18:00 |
| 05:30 | 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 IST to AST Time Conversion
Converting time between India Standard Time (IST) and Atlantic Standard Time (AST) is essential for coordinating between India and Atlantic Canada. IST is UTC+5:30 (consistent year-round, no daylight saving time), while AST is UTC-4 (Atlantic Standard Time, typically November to March). IST is 9.5 hours ahead of AST.
This conversion is important for Indian companies coordinating with Atlantic Canadian offices in Halifax, Saint John, and other major cities. Software development teams, business operations, and enterprises bridging India and Atlantic Canada operations rely on accurate time conversions. Atlantic Canada observes daylight saving time, transitioning to ADT (Atlantic Daylight Time, UTC-3) from March to November, which reduces the offset to 8.5 hours. Understanding when AST transitions to ADT is crucial for scheduling, as the difference changes from 9.5 to 8.5 hours.
Common Use Cases for IST to AST Conversion
Business & Work
- Scheduling calls between Indian offices and Atlantic Canadian headquarters
- Coordinating software development teams across India and Atlantic Canada
- Managing business operations with Atlantic region clients and partners
- Planning conference calls for product development and support teams
Personal & Travel
- Coordinating with family and friends in Atlantic Canada
- Planning travel between India and Atlantic Canada destinations
- Scheduling virtual meetings with Atlantic Canada relatives or partners
- Arranging online collaboration with Atlantic Canada-based colleagues
Time Zone Information
India Standard Time (IST)
- UTC Offset: UTC+5:30
- IANA Timezone: Asia/Kolkata
- Daylight Saving: No daylight saving time (consistent year-round)
- Major Cities: New Delhi, Mumbai, Bangalore, Hyderabad, Chennai, Kolkata
- Coverage: Entire India (single timezone covering entire nation)
Atlantic Standard Time (AST)
- UTC Offset: UTC-4
- IANA Timezone: America/Halifax
- Daylight Saving: Standard time (first Sunday in November to second Sunday in March)
- Major Cities: Halifax, Saint John, Moncton, St. John's, Newfoundland
- Coverage: Atlantic Canada (winter months)
Quick Reference: IST to AST
Remember: IST is always 9.5 hours ahead of AST. When AST transitions to ADT (second Sunday in March), the difference becomes 8.5 hours.
Frequently Asked Questions
What is the time difference between IST and AST?
India Standard Time (IST) is UTC+5:30, while Atlantic Standard Time (AST) is UTC-4. This means IST is 9.5 hours ahead of AST. When you have 8:00 AM in Halifax (AST), it's 5:30 PM the same day in India (IST).
Does the IST to AST difference change throughout the year?
Yes, it varies between 8.5 and 9.5 hours. India doesn't observe daylight saving time, but Atlantic Canada does. From November to March, AST is UTC-4 (9.5 hours behind IST). From March to November, the region observes ADT (Atlantic Daylight Time, UTC-3), making the difference 8.5 hours.
When does AST change to ADT (Atlantic Daylight Time)?
AST transitions to ADT on the second Sunday in March at 2:00 AM AST. This is when the time difference with IST changes from 9.5 to 8.5 hours. The transition back to AST happens on the first Sunday in November at 2:00 AM ADT.
What is Atlantic Canada and which cities are in this timezone?
Atlantic Canada includes the provinces of Nova Scotia, New Brunswick, Prince Edward Island, and Newfoundland and Labrador. Major cities include Halifax, Saint John, Moncton, and St. John's. This region is important for various industries including maritime, technology, and business operations.
What are the overlapping business hours between IST and AST?
The overlap is relatively good compared to US West Coast. Early morning India (8-10 AM IST) aligns with late evening Atlantic time (10:30 PM - 12:30 AM AST previous day). Evening India (6-9 PM IST) aligns with early morning Atlantic time (8:30-11:30 AM AST). These windows offer reasonable meeting times for both regions.
How do I schedule calls between India and Atlantic Canada?
The best windows are 8-10 AM IST / 10:30 PM - 12:30 AM AST (previous day evening) or 6-9 PM IST / 8:30-11:30 AM AST (next morning). During ADT (March-November), these times shift by one hour earlier on the Atlantic side. Atlantic Canada offers better overlap than West Coast, making it easier to find meeting times.
Pro Tips
- • Atlantic Canada is one hour ahead of US Eastern time, giving it better overlap with India compared to West Coast US timezones.
- • The 9.5-hour AST difference (or 8.5 during ADT) is manageable - you have decent business hour overlap unlike more western US regions.
- • Set calendar reminders for March and November when AST/ADT transitions occur and all meeting times shift by one hour.
- • Best meeting windows: 8-10 AM IST for late evening Atlantic calls, or 6-9 PM IST for early morning Atlantic calls.
- • Use timezone-aware scheduling tools that account for AST/ADT transitions and IST consistency year-round.
- • Always confirm meeting times with both IST and AST/ADT clearly specified to avoid confusion during daylight saving transitions.
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