Countdown Timer

How this calculation works

The timer records the wall-clock moment it should end and computes the remainder from the current time on every frame. That sounds like a detail and it is the whole difference in accuracy: a timer built on an interval and a decrementing counter drifts, because intervals fire late under load and are throttled hard in an inactive tab — often to once a minute. A counting timer set for twenty-five minutes can finish several minutes late; this one is simply correct when you come back to it.

What the results mean

Ends at

The clock time the countdown will finish. Worth glancing at — it is the value the timer is actually working from.

Background accuracy

The remaining time is computed, not counted, so a throttled or suspended tab cannot make it run long.

The chime

A short tone played in the page. Browsers may hold it until the tab is active again, which is a platform behaviour rather than a missed alarm.

Common problems and fixes

The chime did not play

Browsers block audio until a page has been interacted with, and hold it in inactive tabs. Pressing start counts as the interaction; a background tab may still wait until you return.

I reloaded the page and lost the timer

Nothing is stored, deliberately. For anything that has to survive a closed tab, use a calendar entry or a phone timer.

The display stutters

The rendering can stutter under load and the total cannot — the end time is fixed and the remainder recomputed each frame.

Frequently asked questions

More in Time

• Epoch / Unix Timestamp ConverterConvert a Unix timestamp to a date and back — in UTC, unambiguously.
• Date Difference CalculatorDays, weeks, months and weekdays between two dates — counted the way people mean.