IST to AST Converter

Convert time between India Standard Time (IST) and Atlantic Standard Time (AST)

India Standard Time (IST)

04:59:45
UTC +0
Jan 04, 2026
Asia/Kolkata

Atlantic Standard Time (AST)

04:59:45
UTC +0
Jan 04, 2026
America/Halifax

Time Difference

Atlantic Standard Time (AST) is 0 hours ahead of India Standard Time (IST)

Select Date

Select Time

Quick Reference

ISTAST
07:3022:00
09:3000:00
11:3002:00
13:3004:00
15:3006:00
17:3008:00
19:3010:00
21:3012:00
23:3014:00
01:3016:00
03:3018:00
05:3020:00

Top 10 Most Common Time Zones

AbbreviationFull NameUTC OffsetTypical Use
UTCCoordinated Universal TimeUTC ±0Global reference standard (servers, logs, APIs)
EST / EDTEastern (US) TimeUTC −5 / −4New York, Toronto — North American business hub
CST / CDTCentral (US) TimeUTC −6 / −5Chicago, Dallas — US central business region
PST / PDTPacific (US) TimeUTC −8 / −7San Francisco, Los Angeles — tech industry standard
GMT / BSTGreenwich Mean / British Summer TimeUTC 0 / +1UK, used globally as a reference with UTC
CET / CESTCentral European (Summer) TimeUTC +1 / +2Paris, Berlin, Amsterdam — EU business core
ISTIndia Standard TimeUTC +5:30India — major IT & outsourcing region
CSTChina Standard TimeUTC +8Beijing, Shanghai — East Asia business hub
JSTJapan Standard TimeUTC +9Tokyo — finance & tech hub
AEST / AEDTAustralian Eastern (Daylight) TimeUTC +10 / +11Sydney, 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 OffsetRegion(s)
CSTCentral Standard Time / China Standard Time / Cuba Standard TimeUTC−6 / UTC+8 / UTC−5North America, China, Cuba
ISTIndian Standard Time / Irish Standard Time / Israel Standard TimeUTC+5:30 / UTC+1 / UTC+2India, Ireland, Israel
ASTAtlantic Standard Time / Arabia Standard TimeUTC−4 / UTC+3Caribbean, Canada, Middle East
PSTPacific Standard Time / Philippine Standard TimeUTC−8 / UTC+8North America, Philippines
ESTEastern Standard Time (North America / Australia)UTC−5 / UTC+10North America, Australia

✅ Best Practice

To avoid ambiguity, always:

  • Use IANA tz identifiers — e.g., America/New_York instead of "EST"
  • Specify UTC offset explicitly — e.g., UTC−5 when abbreviations must be used
  • Include the full timezone name — e.g., "Eastern Standard Time (EST)" with UTC offset

Related Time Zone Conversions

EST to MST EST to MDT MST to EST MDT to EST MDT to EDT MDT to EET

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

8:00 AM IST
10:30 PM AST (previous day)
12:00 PM IST
2:30 AM AST
6:00 PM IST
8:30 AM AST
9:00 PM IST
11:30 AM 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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