IST to AEST time converter

How far apart are Kolkata and Sydney?

It depends on the date. Sydney is 5 hours 30 minutes ahead of Kolkata while Kolkata is on IST and Sydney on AEDT. Sydney is 4 hours 30 minutes ahead of Kolkata while Kolkata is on IST and Sydney on AEST. The exact dates for 2026 and 2027 are below, worked out from the same time zone database your browser uses — not remembered.

2026

2027

IST to AEST hour table

Every hour of a Kolkata day, read across to Sydney — one column per gap, so pick the column for today's date from the table above. A row marked +1 day is already tomorrow there; −1 day is still yesterday.

Each column is one value of the gap; the clock names under it are the ones in force when that gap applies. For a half-hour time or a third city, use the timeline above: every clock moves to the instant you pick.

Working across Kolkata and Sydney

Sydney is ahead of India by four and a half hours for half the year and five and a half for the other half, and the half that applies is the opposite of what a northern-hemisphere instinct expects. Australia's east coast puts its clocks forward on the first Sunday in October — the start of the southern summer — and back on the first Sunday in April. So the gap to India is larger through the Indian winter, when Sydney is on Australian Eastern Daylight Time at UTC+11, and smaller from April to October, when Sydney is on standard time at UTC+10. India itself keeps UTC+5:30 throughout; every change here is Australian.

For the many Indian teams that support Australian companies the overlap is workable but front-loaded. A Sydney nine-to-six day runs from 4:30am to 1:30pm in India under AEST and from 3:30am to 12:30pm under AEDT, so the shared hours are India's morning against Sydney's afternoon: 9am to 1:30pm Indian time in the Australian winter, 9am to 12:30pm in the Australian summer. Indian teams on this corridor commonly start at 7 or 8am to gain another hour or two; the daylight bands on the timeline above show how much of Sydney's afternoon that actually buys. There is no overlap at all in the other direction — by the time India finishes, Sydney has been asleep for hours.

Australia does not have one time zone, and this page uses Sydney's. Melbourne, Canberra and Hobart keep the same clock and change on the same dates. Brisbane and the rest of Queensland stay on AEST all year and do not observe daylight saving, so from October to April Brisbane is an hour behind Sydney and only four and a half hours ahead of India. Perth is on AWST, UTC+8, all year — two and a half hours ahead of India, the same clock as Singapore. Adelaide is on a half-hour offset of its own. If the office is not in Sydney or Melbourne, add the actual city in the tool above.

The abbreviations are cleaner than most. AEST and AEDT mean one thing each, though people routinely write AEST all year when for six months Sydney is on AEDT, so a "10am AEST" invite in December most likely means 10am on a Sydney clock, which is AEDT. IST is the ambiguous side, also standing for Israel Standard Time and Irish Standard Time. The tool above uses the IANA zones Asia/Kolkata and Australia/Sydney and applies whichever Australian rule is in force on the day shown.

The calendar date changes early on this pair: from about 6:30pm or 7:30pm in India, depending on the season, it is already tomorrow in Sydney. A deadline set for "end of day Friday" in Sydney is Friday lunchtime in India, and a Monday 9am Sydney start is before dawn on Monday in Bengaluru. The hour table marks those rows. A Unix timestamp has no time zone of its own — decode it in the epoch converter first, then read the result here.

Sources

The offsets, dates and hour tables above are computed when this page is built, from the time zone rules your browser itself ships. The rules come from:

• IANA Time Zone Database — the rules every browser ships
• ECMA-402 — the Intl.DateTimeFormat standard these figures are computed with