IST to AST
-9h 30mIST
ISTSOURCEAST
ASTGreen rows indicate typical business hours (9 AM - 5 PM)
IST and AST on the World Map
The map below highlights the IST (India Standard Time) and AST (Atlantic Standard Time) timezone regions across the globe.
IST – India Standard Time
UTC+05:30India Standard Time (IST) is the time zone for India and Sri Lanka, 5 hours and 30 minutes ahead of UTC.
- •India is 10 hours 30 minutes ahead of EST and 5 hours 30 minutes ahead of GMT.
- •India uses a single time zone despite spanning 30° of longitude.
- •IST is one of only a handful of time zones with a 30-minute offset.
- •IST is the most populous single time zone in the world with over 1.4 billion people.
- •The Bombay Stock Exchange (BSE) and National Stock Exchange (NSE) operate on IST.
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.
Understanding the -9h 30m Gap: IST vs AST
IST runs on India Standard Time (IST) at UTC+05:30. AST runs on Atlantic Standard Time (AST) at UTC-04:00. That puts IST 9 hours 30 minutes behind AST — a difference of -9h 30m at the current offsets.
In practice, when it is 9:00 AM in IST it is 11:30 PM in AST on the previous day. Midnight in IST is 2:30 PM in AST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
IST to AST time conversion table
| IST (IST) | AST (AST) | Day |
|---|---|---|
| 12:00 AM | 2:30 PM | previous day |
| 6:00 AM | 8:30 PM | previous day |
| 7:00 AM | 9:30 PM | previous day |
| 8:00 AM | 10:30 PM | previous day |
| 9:00 AM | 11:30 PM | previous day |
| 12:00 PM | 2:30 AM | same day |
| 3:00 PM | 5:30 AM | same day |
| 5:00 PM | 7:30 AM | same day |
| 6:00 PM | 8:30 AM | same day |
| 9:00 PM | 11:30 AM | same day |
Why people convert IST to AST time
- Scheduling a call from IST to AST: a 10:00 AM start in IST lands at 12:30 AM in AST, so you can confirm the slot without doing the arithmetic yourself.
- Handling a -9h 30m gap: IST and AST have no overlap inside a normal 9-to-5 day, so real-time meetings need an early-morning or late-evening slot on one side. 9:00 AM in AST is 11:30 PM in IST.
- Coordinating a IST-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 IST" is unambiguous; "3 PM" across a -9h 30m gap is not.
- With a -9h 30m gap there is no shared 9-to-5 window, so alternate the early start: one week IST takes the early slot, the next week AST does.
About IST (India Standard Time)
India Standard Time (IST) is the time observed throughout India and Sri Lanka. It is based on the 82.5°E meridian, passing through Mirzapur in Uttar Pradesh. India uses a single time zone despite spanning roughly 30° of longitude, which has been debated. IST does not observe daylight saving time. India is the world's most populous country, making IST one of the most-used time zones globally. The IT outsourcing industry and call centers operate primarily on IST, making the EST-to-IST conversion one of the most searched timezone conversions.
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 IST and AST
With a -9h 30m offset there is no overlap inside a normal 9 AM – 5 PM day. AST opens at 9:00 AM AST, which is 11:30 PM in IST, so real-time calls need an early-morning or late-evening slot on one side.
Business hours overlap
IST and AST have no shared working hours because of the -9h 30m gap. Teams need to alternate early starts or rely on asynchronous handovers.
IST is 9 hours 30 minutes behind AST (IST UTC+05:30 → AST UTC-04:00). There is no shared 9-to-5 window, so plan around an early or late slot. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
IST
Does not observe DST
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 IST and AST?
IST (IST, UTC+05:30) is 9 hours 30 minutes behind AST (AST, UTC-04:00). The gap is currently -9h 30m.
How do I convert IST time to AST time?
Add -9h 30m to IST local time. For example, 9:00 AM in IST is 11:30 PM in AST (previous day).
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 -9h 30m offset from IST.
What is the best time to call AST from IST?
There is no shared working-hours window because of the -9h 30m gap. The closest option is 1:00 PM in IST, which is 3:30 AM in AST.
Which is behind, IST or AST?
IST is 9 hours 30 minutes behind AST. When it is 12:00 PM in IST it is 2:30 AM in AST.
Does daylight saving time affect the IST–AST difference?
Neither zone observes daylight saving time, so the -9h 30m offset between IST and AST is fixed all year.
Which other cities share IST's time zone?
IST also covers Mumbai, Delhi, Bangalore, Kolkata, Chennai, Hyderabad, Pune, Ahmedabad and 4 more.
Which countries use IST, IST's zone?
IST is used in India, Sri Lanka.
Is there a day difference between IST and AST?
Not normally. The -9h 30m gap only pushes the date over the previous day.
What is the time difference between IST and AST?
AST is -9h 30m from IST.
What timezone is IST in?
IST operates on its local timezone.
What timezone is AST in?
AST operates on its local timezone.
Which countries use IST (India Standard Time)?
IST is used in India, Sri Lanka.
Does IST observe daylight saving time?
No, IST does not observe daylight saving time and remains at UTC+05:30 year-round.
What are some interesting facts about IST?
India is 10 hours 30 minutes ahead of EST and 5 hours 30 minutes ahead of GMT. India uses a single time zone despite spanning 30° of longitude.
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 IST, what time is it in AST?
When it is 12:00 AM (midnight) in IST (IST), it is -9h 30m later in AST (AST).
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