Colombo to ACST
+4hColombo
ISTSOURCEACST
ACSTGreen rows indicate typical business hours (9 AM - 5 PM)
IST and ACST on the World Map
The map below highlights the IST (India Standard Time) and ACST (Australian Central 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.
ACST – Australian Central Standard Time
UTC+09:30Australian Central Standard Time (ACST, UTC+09:30) covers South Australia and the Northern Territory, on a half-hour offset.
- •ACST uses a half-hour offset: UTC+09:30.
- •South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
- •Adelaide and Darwin are 30 minutes apart during daylight saving, level in winter.
- •Adelaide is one of the few major cities on a 30-minute offset.
About Colombo
WikipediaColombo operates on Sri Lanka Time (SLST), UTC+5:30. Sharing India's timezone, Colombo is a key South Asian trade and tourism hub.
Sri Lanka Standard Time (SLST) uses UTC+5:30, same offset as India.
Time Conversion Guide: Colombo to ACST
Colombo runs on India Standard Time (IST) at UTC+05:30. ACST runs on Australian Central Standard Time (ACST) at UTC+09:30. That puts Colombo 4 hours ahead of ACST — a difference of +4h at the current offsets.
In practice, when it is 9:00 AM in Colombo it is 1:00 PM in ACST. Midnight in Colombo is 4:00 AM in ACST. Neither zone observes daylight saving time, so the offset between them stays constant all year.
Colombo to ACST time conversion table
| Colombo (IST) | ACST (ACST) | Day |
|---|---|---|
| 12:00 AM | 4:00 AM | same day |
| 6:00 AM | 10:00 AM | same day |
| 7:00 AM | 11:00 AM | same day |
| 8:00 AM | 12:00 PM | same day |
| 9:00 AM | 1:00 PM | same day |
| 12:00 PM | 4:00 PM | same day |
| 3:00 PM | 7:00 PM | same day |
| 5:00 PM | 9:00 PM | same day |
| 6:00 PM | 10:00 PM | same day |
| 9:00 PM | 1:00 AM | next day |
Why people convert Colombo to ACST time
- Scheduling a call from Colombo to ACST: a 10:00 AM start in Colombo lands at 2:00 PM in ACST, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both Colombo and ACST are inside the 9-to-5 working day between 9:00 AM and 1:00 PM IST time (1:00 PM–5:00 PM ACST). That is roughly 4 hours of usable overlap.
- Booking travel or deliveries: tracking ACST local time against Colombo keeps pickup windows and arrival estimates honest across the +4h offset.
- Always state the zone abbreviation, not just the hour. "3:00 PM IST" is unambiguous; "3 PM" across a +4h gap is not.
- Block 9:00 AM–1:00 PM IST as the recurring meeting window if you work primarily from Colombo and need ACST colleagues present.
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 ACST (Australian Central Standard Time)
Australian Central Standard Time (ACST) is the half-hour offset of UTC+09:30 used across South Australia and the Northern Territory, taking in Adelaide and Darwin. South Australia moves to Australian Central Daylight Time (ACDT, UTC+10:30) from the first Sunday in October to the first Sunday in April, but the Northern Territory does not observe daylight saving — so Adelaide and Darwin sit 30 minutes apart in summer and level with each other in winter. The half-hour offset means Adelaide is 30 minutes behind Sydney in winter and level with it during daylight saving, which regularly catches out travellers and meeting planners.
Best time to call between Colombo and ACST
Both Colombo and ACST sit inside the 9 AM – 5 PM working day between 9:00 AM–1:00 PM IST, which is 1:00 PM–5:00 PM ACST. That gives roughly 4 hours of shared time — the safest window for a live call or meeting.
Business hours overlap
Colombo and ACST overlap for about 4 hours during the working day — enough for meetings if you avoid the edges of the window.
Colombo is 4 hours ahead of ACST (IST UTC+05:30 → ACST UTC+09:30). The shared working window is 9:00 AM–1:00 PM IST. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
Colombo
Does not observe DST
ACST
❄ Currently in Standard Time
Standard: UTC+09:30 · DST: UTC+10:30
Clocks spring forward on Sat, Oct 3, 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 Colombo and ACST?
Colombo (IST, UTC+05:30) is 4 hours ahead of ACST (ACST, UTC+09:30). The gap is currently +4h.
How do I convert Colombo time to ACST time?
Add +4h to Colombo local time. For example, 9:00 AM in Colombo is 1:00 PM in ACST.
What time is it in ACST right now?
ACST uses ACST at UTC+09:30. Use the live converter at the top of this page — it updates in real time and already accounts for the +4h offset from Colombo.
What is the best time to call ACST from Colombo?
Call between 9:00 AM and 1:00 PM IST — that maps to 1:00 PM–5:00 PM ACST and keeps both parties inside the working day.
Which is ahead, Colombo or ACST?
Colombo is 4 hours ahead of ACST. When it is 12:00 PM in Colombo it is 4:00 PM in ACST.
Do Colombo and ACST use different time zones?
Colombo (Sri Lanka) uses IST at UTC+05:30, while ACST uses ACST at UTC+09:30. The IANA identifiers are Asia/Colombo and Australia/Adelaide.
Does daylight saving time affect the Colombo–ACST difference?
Neither zone observes daylight saving time, so the +4h offset between Colombo and ACST is fixed all year.
Which other cities share Colombo's time zone?
IST also covers Mumbai, Delhi, Bangalore, Kolkata, Chennai, Hyderabad, Pune, Ahmedabad and 4 more.
Which countries use IST, Colombo's zone?
IST is used in India, Sri Lanka.
Is there a day difference between Colombo and ACST?
Not normally. The +4h gap only pushes the date over for late-evening times.
What is the time difference between Colombo and ACST?
ACST is +4h from Colombo.
What timezone is Colombo in?
Colombo operates on Sri Lanka Time (SLST), UTC+5:30. Sharing India's timezone, Colombo is a key South Asian trade and tourism hub.
What timezone is ACST in?
ACST operates on its local timezone.
What are the business hours in Colombo?
Standard business hours in Colombo are 9:00 AM - 5:00 PM IST.
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 ACST timezone?
Major cities in the ACST timezone include Adelaide, Darwin, Alice Springs, Mount Gambier.
What is the UTC offset for ACST?
Australian Central Standard Time (ACST) is at UTC+09:30. During daylight saving time, it shifts to ACDT.
What should I know about the ACST timezone?
ACST uses a half-hour offset: UTC+09:30. South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
When is it midnight in Colombo, what time is it in ACST?
When it is 12:00 AM (midnight) in Colombo (IST), it is +4h later in ACST (ACST).
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