Offsets are not fixed
A time zone is a region that follows the same clock rules, identified by names like Europe/London or Asia/Shanghai in the IANA time zone database that phones and computers use. Each zone has an offset from Coordinated Universal Time (UTC), and in many zones that offset changes during the year because of daylight saving time (DST). Some offsets are not whole hours: India is UTC+5:30 and Nepal UTC+5:45.
| City | January | April | Daylight saving |
|---|---|---|---|
| New York | UTC−5 | UTC−4 | 2nd Sunday of March to 1st Sunday of November |
| London | UTC+0 | UTC+1 | last Sunday of March to last Sunday of October |
| Beijing | UTC+8 | UTC+8 | none |
| Sydney | UTC+11 | UTC+10 | first Sunday of October to first Sunday of April |
| Auckland | UTC+13 | UTC+12 | last Sunday of September to first Sunday of April |
Because Sydney and Auckland are in the southern hemisphere, their summer time runs during the northern winter. The gap between Sydney and London is 11 hours in January and 9 hours in April. The time zone converter works from the zone name, not a fixed offset, so it always uses the offset in force on the date you pick.
Finding the hours that overlap
Add each participant's city to the time zone converter and choose a date; the grid shows every hour of that day in each city and highlights the hours that fall within working time (9:00 to 18:00, Monday to Friday) everywhere. For Monday 5 October 2026:
- London and New York share four hours: 14:00 to 18:00 in London, which is 9:00 to 13:00 in New York.
- Beijing and London share two hours: 16:00 to 18:00 in Beijing, 9:00 to 11:00 in London.
- Beijing and New York share none. 21:00 in Beijing is 9:00 the same day in New York.
- London, New York and Beijing together share none.
When there is no common hour, someone has to meet outside their working day. The fair approach is to rotate who that is, rather than leaving it permanently with the smallest office. Another is to split the meeting: a Europe–Asia session and a Europe–Americas session, with London attending both. For many decisions, a written update that each office reads in its own morning works better than any call.
The weeks when everything shifts
Europe and North America change their clocks on different dates, so for a few weeks every spring and autumn the usual differences are wrong. In 2026, Europe ends summer time on 25 October and the United States on 1 November. Take a weekly call fixed at 15:00 London time on Mondays:
| Monday | London | New York | Beijing |
|---|---|---|---|
| 19 October | 15:00 | 10:00 | 22:00 |
| 26 October | 15:00 | 11:00 | 23:00 |
| 2 November | 15:00 | 10:00 | 23:00 |
For one week New York joins an hour later than usual; from November, Beijing is permanently an hour later until spring, because China does not use daylight saving. The same happens in reverse in March: in 2026 the United States moves its clocks on 8 March and Europe on 29 March, so for three weeks London and New York are four hours apart instead of five.
Calendar software handles this correctly if the meeting is created in one named time zone. Problems start when someone copies the time into a message as "3 pm UK / 10 am NY" — that text does not update. Before the change weeks, check the converter for the dates in question and send a short reminder to whoever is affected.
Times that do not exist, and times that happen twice
On the morning the clocks go forward, an hour is skipped: in New York on 8 March 2026 the clock jumps from 2:00 to 3:00, so 2:30 never happens. On the morning they go back, an hour is repeated: 1:30 on 1 November 2026 happens twice in New York. The converter warns you when you pick either kind of time, and tells you which moment it has used. Avoid scheduling anything automatic — backups, reports, reminders — in those hours.
Writing times nobody can misread
- Name the city or zone, not the abbreviation. CST can mean China Standard Time (UTC+8) or US Central Standard Time (UTC−6); IST is used for India, Ireland and Israel. "15:00 London time" or "15:00 Europe/London" is unambiguous.
- Include the date. A call at 09:00 in New York on Monday is 21:00 on Monday in Beijing, but a call at 18:00 in Los Angeles on Friday is already Saturday in Tokyo.
- Use the 24-hour clock or say am/pm clearly. "12 am" confuses many readers; "00:00" or "midnight at the start of 3 March" does not.
- For deadlines, give the moment in UTC as well. "Submissions close 23:59 UTC on 31 October 2026" is the same instant for every reader, and they can convert it once.
- Use ISO dates in anything written for machines: 2026-10-31T23:59:00Z is readable by people and parsers alike.
Counting days to a deadline
The date calculator answers the other half of scheduling: how long until, and what date is it in N days. From 28 September 2026 to 25 December 2026 is 88 days, or 12 weeks and 4 days, of which 64 are weekdays. Ten business days after 28 September 2026 is 12 October 2026, and 30 calendar days after is 28 October.
Two rules of thumb avoid off-by-one arguments. First, say whether the count includes the start day; the date calculator counts the days between two dates, so a start on Monday and an end on Tuesday is one day. Second, adding a month to 31 January gives 28 February in 2026, because there is no 31 February; contracts and payment schedules usually spell out what happens in that case, and so should you.
Business-day counts in the calculator skip Saturdays and Sundays only. Public holidays differ by country and, in China, by the yearly adjustment of working weekends, so check the official holiday calendar when a deadline falls near one. For the final stretch, the countdown timer counts down to a date and time and stays accurate in a background tab. Note that a shared countdown link carries a clock time, not a single moment: a colleague in another city counts down to that clock time where they are. That is right for "midnight on New Year's Eve", but for one global deadline, convert it first and let each person set the countdown in their own local time.
A checklist for international scheduling
- Put every participant's city in the converter, and look at the actual date, not a typical week.
- Choose a slot inside everyone's working hours; if there is none, rotate the inconvenience.
- Create the meeting in one named time zone in a calendar that everyone subscribes to.
- Check the March and October–November change weeks ahead of time.
- In writing, give the date, the time, and the city or UTC — never an abbreviation alone.
Limits
- Time zone rules come from your browser. They are updated with the browser and operating system; a government that changes its rules at short notice may not be reflected until the next update.
- Working hours are fixed at 9:00–18:00, Monday to Friday. Teams with different hours or weekends (for example Sunday to Thursday) should read the grid with that in mind.
- Business days skip weekends only, not public holidays.
Frequently asked questions
What time is best for a meeting between London and New York?
Usually 14:00–17:00 London time, which is 9:00–12:00 in New York. Check the date: for a few weeks in March and autumn the gap is four hours instead of five.
Why did my recurring meeting move by an hour?
The meeting is fixed in one city's time, and another city changed its clocks for daylight saving on a different date or not at all.
How should I write a deadline for people in different countries?
Give the date, the time and the zone as a city or UTC, for example 23:59 UTC on 31 October 2026. Avoid abbreviations like CST or IST, which mean different zones in different countries.