What happens at a DST-skipped local time?

The countdown flags it and uses the standard forward-shifted convention, rather than silently guessing at a local time that never actually occurred.

Does the countdown keep running if the browser tab is in the background?

It continues counting since it is anchored to the real target instant rather than to elapsed ticks, so reopening the tab shows the correct remaining time immediately, even after a long gap.

Countdown to Date Timer

Enter a target date, time, and zone. See a live countdown (or count-up, if the date has already passed).

Target date

Target time

Zone

Just need a plain duration countdown, not a specific calendar date? See Timer.

Want to learn more?

Countdown and Count-Up Are the Same Math

Worked example

A target set for 6:00 PM Eastern Time on a future date shows a live countdown that ticks down every second toward that specific real instant, converted correctly regardless of the browser's own local zone. Set that same target date to one that already passed instead, and the display flips automatically to counting up the elapsed time since that moment, rather than showing a meaningless negative countdown.

Common mistakes

Forgetting to set the correct time zone for the target. The countdown is computed against the real instant the target represents, not just the raw numbers typed into the date and time fields.
Assuming the countdown sends a reminder or notification on its own when it reaches zero. It only updates the on-screen display while the tab stays open.

Limitations

This is a browser-local utility with no persistence or notification of its own. It does not send an alert or reminder when the countdown reaches zero, so the tab needs to stay open and visible to be useful as a live display.

Frequently asked questions

What happens at a DST-skipped local time?: The countdown flags it and uses the standard forward-shifted convention, rather than silently guessing at a local time that never actually occurred.
Does the countdown keep running if the browser tab is in the background?: It continues counting since it is anchored to the real target instant rather than to elapsed ticks, so reopening the tab shows the correct remaining time immediately, even after a long gap.