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Countdown timer

Count down a duration or a fixed local deadline with an explicitly chosen UTC offset, verified against the browser’s time zone.

Time is calculated from the device clock, not display ticks. Returning recalculates elapsed time, including skipped phases. Changing the device clock affects the result. Background operation or alerts are not guaranteed; there is no audio or autosave.

Duration is one second to 7 days and can be paused and resumed from the remaining time. A deadline is fixed within 366 days; stopping clears the session without moving its target. Start it again to calculate the time remaining to the same target.

Timer settings

Fields allow up to 32 UTF-16 units without truncation. Numbers are positive integers; no exponents, spaces or line breaks. Arabic digits are accepted. Changing a unit does not correct an oversized field.

Session controls

How to use

Choose Duration or Fixed local deadline. For a duration, enter seconds and start; you can pause and resume the remaining time. For a deadline, enter its date, time and offset, then start after both are verified against the browser’s zone. A fixed deadline cannot be paused. Stop keeps inputs, and restarting targets the same deadline; Reset clears them after confirmation. Explicitly download countdown-timer.json or copy the snapshot.

Try an example

A 90-second duration initially shows 0:01:30. In a browser using America/New_York, 2024-11-03T01:30:00 with -04:00 identifies 05:30 UTC, while -05:00 identifies 06:30 UTC. This is a historical example of distinguishing repeated local time; the tool rejects deadlines already in the past. In that zone, 2024-03-10T02:30:00 does not exist because of daylight saving.

Support & limits

The offset is that local deadline’s time minus UTC; it is not a zone name or necessarily today’s offset. One candidate instant is calculated from the explicit offset, then every local date/time component and offset is compared with the browser’s local Date. Missing DST times and mismatched offsets are rejected; repeated times are never silently resolved. Both modes depend on the device clock and are affected by changes to it. Returning recalculates state from timestamps rather than counting display ticks. Background alerts or operation are not guaranteed; there is no audio, service worker or automatic storage. Hours can exceed 24, and displayed seconds round upward. A JSON snapshot records the state when clicked and cannot be imported as a session.

Common questions

Why can a fixed deadline not be paused?

A deadline identifies a fixed instant; pausing and moving it would change its meaning. Use Duration to freeze remaining time during a pause. Stopping and restarting a deadline session does not change the entered date, and starting may be rejected if the deadline passed while stopped.

Related tools

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Set a bounded work-and-break plan, start, pause and resume its remaining time, with progress calculated from the device clock.