ACST to Colombo
-4hACST
ACSTSOURCEColombo
ISTGreen rows indicate typical business hours (9 AM - 5 PM)
ACST and IST on the World Map
The map below highlights the ACST (Australian Central Standard Time) and IST (India Standard Time) timezone regions across the globe.
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.
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.
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: ACST to Colombo
ACST runs on Australian Central Standard Time (ACST) at UTC+09:30. Colombo runs on India Standard Time (IST) at UTC+05:30. That puts ACST 4 hours behind Colombo — a difference of -4h at the current offsets.
In practice, when it is 9:00 AM in ACST it is 5:00 AM in Colombo. Midnight in ACST is 8:00 PM in Colombo. Neither zone observes daylight saving time, so the offset between them stays constant all year.
ACST to Colombo time conversion table
| ACST (ACST) | Colombo (IST) | Day |
|---|---|---|
| 12:00 AM | 8:00 PM | previous day |
| 6:00 AM | 2:00 AM | same day |
| 7:00 AM | 3:00 AM | same day |
| 8:00 AM | 4:00 AM | same day |
| 9:00 AM | 5:00 AM | same day |
| 12:00 PM | 8:00 AM | same day |
| 3:00 PM | 11:00 AM | same day |
| 5:00 PM | 1:00 PM | same day |
| 6:00 PM | 2:00 PM | same day |
| 9:00 PM | 5:00 PM | same day |
Why people convert ACST to Colombo time
- Scheduling a call from ACST to Colombo: a 10:00 AM start in ACST lands at 6:00 AM in Colombo, so you can confirm the slot without doing the arithmetic yourself.
- Finding shared working hours: both ACST and Colombo are inside the 9-to-5 working day between 1:00 PM and 5:00 PM ACST time (9:00 AM–1:00 PM IST). That is roughly 4 hours of usable overlap.
- Coordinating a ACST-based team with Colombo 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 ACST" is unambiguous; "3 PM" across a -4h gap is not.
- Block 1:00 PM–5:00 PM ACST as the recurring meeting window if you work primarily from ACST and need Colombo colleagues present.
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.
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.
Best time to call between ACST and Colombo
Both ACST and Colombo sit inside the 9 AM – 5 PM working day between 1:00 PM–5:00 PM ACST, which is 9:00 AM–1:00 PM IST. That gives roughly 4 hours of shared time — the safest window for a live call or meeting.
Business hours overlap
ACST and Colombo overlap for about 4 hours during the working day — enough for meetings if you avoid the edges of the window.
ACST is 4 hours behind Colombo (ACST UTC+09:30 → IST UTC+05:30). The shared working window is 1:00 PM–5:00 PM ACST. Remember to re-check around daylight-saving transitions.
🕐 Daylight Saving Time Info
ACST
❄ Currently in Standard Time
Standard: UTC+09:30 · DST: UTC+10:30
Clocks spring forward on Sat, Oct 3, 2026
Colombo
Does not observe DST
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 ACST and Colombo?
ACST (ACST, UTC+09:30) is 4 hours behind Colombo (IST, UTC+05:30). The gap is currently -4h.
How do I convert ACST time to Colombo time?
Add -4h to ACST local time. For example, 9:00 AM in ACST is 5:00 AM in Colombo.
What time is it in Colombo right now?
Colombo uses IST at UTC+05:30. Use the live converter at the top of this page — it updates in real time and already accounts for the -4h offset from ACST.
What is the best time to call Colombo from ACST?
Call between 1:00 PM and 5:00 PM ACST — that maps to 9:00 AM–1:00 PM IST and keeps both parties inside the working day.
Which is behind, ACST or Colombo?
ACST is 4 hours behind Colombo. When it is 12:00 PM in ACST it is 8:00 AM in Colombo.
Do ACST and Colombo use different time zones?
ACST uses ACST at UTC+09:30, while Colombo (Sri Lanka) uses IST at UTC+05:30. The IANA identifiers are Australia/Adelaide and Asia/Colombo.
Does daylight saving time affect the ACST–Colombo difference?
Neither zone observes daylight saving time, so the -4h offset between ACST and Colombo is fixed all year.
Which other cities share ACST's time zone?
ACST also covers Adelaide, Darwin, Alice Springs, Mount Gambier.
Which countries use ACST, ACST's zone?
ACST is used in Australia (South Australia, Northern Territory).
Is there a day difference between ACST and Colombo?
Not normally. The -4h gap only pushes the date over the previous day.
What is the time difference between ACST and Colombo?
Colombo is -4h from ACST.
What timezone is ACST in?
ACST operates on its local timezone.
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 are the business hours in Colombo?
Standard business hours in Colombo are 9:00 AM - 5:00 PM IST.
Which countries use ACST (Australian Central Standard Time)?
ACST is used in Australia (South Australia, Northern Territory).
Does ACST observe daylight saving time?
Yes, ACST switches to ACDT during summer months.
What are some interesting facts about ACST?
ACST uses a half-hour offset: UTC+09:30. South Australia moves to ACDT (UTC+10:30) in summer; the Northern Territory does not.
Which cities are in the IST timezone?
Major cities in the IST timezone include Mumbai, Delhi, Bangalore, Kolkata, Chennai, Hyderabad, Pune, Ahmedabad.
What is the UTC offset for IST?
India Standard Time (IST) is at UTC+05:30.
What should I know about the IST timezone?
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.
When is it midnight in ACST, what time is it in Colombo?
When it is 12:00 AM (midnight) in ACST (ACST), it is -4h later in Colombo (IST).
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