About this tool
This converter turns a time in Chicago into the matching time in Sydney, or the other way round, for any date you choose. It shows both cities' clocks live, the hour difference on that date, a 24-hour conversion table with next-day markers, the narrow working-hours overlap, and this year's clock-change dates in both cities. Chicago and Sydney both observe daylight saving time but in opposite seasons, so Sydney is 17 hours ahead in the northern winter, 15 hours ahead in the northern summer, and 16 hours ahead for a few weeks around the March-April and October changeovers; the year table shows exactly when each gap applies. Because the difference is close to a full day, most of Chicago's working day is already tomorrow in Sydney. It is built for people scheduling calls between the US Midwest and Australia's east coast, following Australian sport or markets from Chicago, or planning travel between O'Hare and Sydney.
How it works
Both cities are IANA time zones (America/Chicago and Australia/Sydney) and every offset comes from the browser's time zone database through Intl.DateTimeFormat, never from a hard-coded table, so the daylight-saving rules in force on the chosen date are applied automatically. To convert, the wall-clock time you enter is first treated as UTC, the source zone's offset at that guess is subtracted, and the check is repeated once so times on a clock-change day land on the correct side of the change. The resulting instant is then formatted in the other zone to give the local date and time; the day marker is the difference between the two calendar dates. The hour difference shown is the target offset minus the source offset at that instant, and the year table is built by sampling the two offsets at noon UTC on every day of the year and grouping the runs where the difference stays the same.
Frequently asked questions
Is Sydney 15, 16, or 17 hours ahead of Chicago?
All three, depending on the date. The cities observe daylight saving in opposite seasons: 17 hours in the northern winter (Chicago on CST, Sydney on AEDT), 15 hours in the northern summer (CDT and AEST), and 16 hours for roughly four weeks in March-April and again in October when only one city has moved its clocks. In 2026 the 15-hour period runs from April 5 to October 3.
When do the clocks change in Sydney and Chicago?
Sydney starts daylight saving on the first Sunday in October at 2:00 am and ends it on the first Sunday in April at 3:00 am. Chicago moves forward on the second Sunday in March at 2:00 am and back on the first Sunday in November at 2:00 am. Because these four dates never coincide, the hour difference changes four times a year; the table on this page lists the exact dates for the year you pick.
Is it the next day in Sydney?
For most of Chicago's day, yes. From about 7:00 am Chicago time in winter (9:00 am in summer) onward, Sydney has passed midnight and is on the following calendar date, so a Friday afternoon meeting in Chicago is Saturday morning in Sydney. Only in the small hours of the Chicago morning do the two cities share a date.
What time should a Chicago to Sydney call be?
The only overlap of standard 9-to-5 days is 4:00 pm Chicago, which is 9:00 am Sydney in the northern winter; in the northern summer 4:00 pm Chicago is 7:00 am Sydney and there is no overlap. Most teams choose early evening in Chicago (5:00 to 7:00 pm, which is 8:00 am to noon in Sydney depending on the season) or 7:00 am in Chicago, which is 10:00 pm to midnight in Sydney.