Time zones

1. 01Convert: choose a zone, date and time. Below, you see what time it is then in up to eight zones. The “Now” button fills in the current time.
2. 02Find a time: choose a day and enter the working hours for each zone. The bars show when everyone works. The address bnkz.de/en/calculator/time-zones/#termin opens this tab directly.
3. 03Pick a start, then download the calendar file or copy the text with all local times and send it.

Where the times come from. Your browser knows the international time zone database (IANA) with all daylight saving rules. From it, the tool calculates every offset from UTC, including half and three quarter hours as in India (UTC+5:30) or Nepal (UTC+5:45). Europe and the USA change their clocks on different days: so in March and at the end of October there are a few weeks in which New York is only 5 instead of 6 hours behind Berlin. If a clock change is due within two weeks before or after the chosen moment, the zone’s card says so. An older browser may not yet know very recent changes made by individual countries. The calculation covers the years 1970 to 2100, for the future with the rules that apply today.

Times that do not exist or exist twice. When the clocks go forward, an hour is missing: in Berlin there is no 2:30 on 28 March 2027. The tool says so and then calculates with 3:30, as the calendar standard requires. When the clocks go back, an hour happens twice: 2:30 on 31 October 2027 exists in Berlin first in summer time and one hour later again in winter time. Then you choose which one you mean.

Names. Cities have English names where one is stored, otherwise the name from the database (usually English as well). The search also finds German spellings such as Wien or Tokio, names without accents and an offset like UTC+5:30. Several cities can share a zone: San Francisco works like Los Angeles.

Find a time. The bars show the chosen day of the first zone from 0:00 to 24:00, and below that, for each zone, what time it is there at that moment. Any quarter hour of this day can be a start, from 0:00 to 23:45. A late meeting may run past midnight; in the bar it is then open on the right. On the day the clocks go back, some start times exist twice; they appear in the list with (1) for the first and (2) for the second time. The up arrow moves a zone one place forward until it is the first. Working hours may run past midnight, for example 22:00 to 06:00. If “Saturday and Sunday are off” is on, there are no working hours on those days. In some countries the weekend is Friday and Saturday, and the tool does not know public holidays at all: check that yourself.

If there is no shared time, the tool suggests, out of all start times of the day, the ones with the lowest burden. This is how it counts: every minute of the meeting that falls outside someone’s working hours counts once. If it also falls between 22:00 and 7:00 local time, it counts twice. The sum over everyone is the burden. With an equal sum, the meeting where nobody gets a particularly large share wins. This is a simple rule of thumb, not the truth: only each person knows whether they would rather get up early or stay up late.

Calendar file. The file (.ics) holds the meeting with times in UTC. Calendar apps such as Outlook, Google Calendar or Apple Calendar convert it to the device’s zone when they open it, so it is right for everyone who gets it. The description lists all local times. It only becomes an invitation with accept and decline when you send it from your calendar.