Daylight saving time explained

One hour can change the whole plan

Daylight saving time (DST) changes the relationship between local clock time and UTC for part of the year. Many places move their clocks forward in spring and back in autumn, but the dates and size of the change are not universal.

A city-based time zone, such as America/New_York, includes these rules. A fixed offset, such as UTC−5, does not. Choose a city in the converter when you mean the time people will actually see on their clocks.

The weeks when the usual difference is wrong

Different regions can change their clocks on different weekends. During the interval between changes, a familiar time difference can temporarily be an hour shorter or longer.

For example, a New York–London meeting should be checked for its actual date. Do not assume a time difference you used in January is correct for every week in March or October. Use the date picker before sharing a meeting.

Some times do not exist. Others happen twice.

When a clock jumps from 1:59 am to 3:00 am, a local appointment at 2:30 am cannot happen on that date. The converter flags this skipped time so you can choose another.

When clocks move back, a local time can occur twice. The time editor lets you select the first or second occurrence and shows which UTC offset is being used. This matters especially for travel, overnight work, and event logs.

A practical checklist for recurring meetings

Use the organizer’s city time zone in your calendar, rather than a fixed UTC offset. Check the meeting dates around clock changes in every participant’s location. Put the date and city in written invitations.

Our calendar download creates one event at a specific instant. If you make it recurring in your calendar app, choose the intended city time zone and review future occurrences. Rotating the inconvenient slot can make recurring global meetings fairer.

Where the rules come from

Time zone policies can change. This site calculates offsets using the time zone data included in your browser or operating system. Keep your device updated, particularly when a country announces a new clock policy. Historical data and future rules have practical limits; see our accuracy page for details.