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Time zone guides

Plain-English answers to the questions that cause missed meetings.

Short, practical references for anyone who works across time zones. Every date and offset on these pages is computed from the IANA time zone database (2026c), the same data your phone and calendar use, and each guide is reviewed when the rules change.

• Daylight saving time 2026–2027: every clock change that affects international meetings

  When the clocks change in each major region, the weeks when the usual gaps between cities are wrong, and the countries that never change.

• Working-hour overlap between major business cities

  How much of the working day two cities actually share, how that changes through the year, and what to do when the answer is zero.

• UTC vs GMT: what is the difference?

  A time standard, a time zone, and the summer-time mistake that catches people out every year.

• Time zone abbreviations that cause mix-ups

  IST, CST, BST and AST each mean more than one thing. Here is what they mean, and what to write instead.

• Half-hour and 45-minute time zones, explained

  India, Nepal, Newfoundland and a dozen other places keep clocks that are not a whole number of hours from UTC.

Tools

• World clock: current time anywhere, with the next clock change.
• Time zone converter: convert a time between cities.
• Meeting time matcher: rank the fairest slots for two to six people.