About Countdown Timers
A countdown timer counts down from a set duration to zero. Where a stopwatch measures how long something takes, a countdown tells you when a fixed period has elapsed. They are used for cooking, exams, presentations, workouts, meetings, meditation, focus sessions and any situation where a specific amount of time needs to pass.
This tool is designed for one job — setting a duration and starting a countdown — and does it well. It supports custom durations, quick presets, shareable URLs, wake lock, an alarm that loops until dismissed, and a big screen mode for projecting a timer onto a wall or TV.
How it works
The countdown uses performance.now() to compute remaining time from a start timestamp, so it stays accurate even when the browser throttles background tabs. The display updates every animation frame for a smooth, precise countdown.
Colour-coded urgency
The display shifts colour as time runs out, so you can see urgency at a glance without reading the numbers:
| Time remaining | Colour | Meaning |
|---|---|---|
| Normal | Green | Plenty of time left |
| Under 60 s | Amber | Wrap up — nearly done |
| Under 10 s | Red | Final seconds |
| Finished | Flashing red | Time is up |
Big screen mode
Big screen mode hides the header, footer, ads and configuration panels, then puts the page in fullscreen with a giant timer display. It is designed for projecting a timer onto a classroom board, event screen or wall-mounted TV. The display scales to fill the whole screen and keeps the timer name, status and progress bar visible.
Trigger it with the expand button in the top-right of the timer stage, or press F. Exit with Esc or the exit button.
Wake lock
Long timers running on a phone or laptop will usually be interrupted by the screen dimming and locking. Wake lock is a browser API that keeps the screen on. Enable it with the lightbulb button before starting — the icon fills in when the lock is active.
Wake lock is supported in Chrome, Edge, Safari and most modern mobile browsers. On unsupported browsers the button shows a brief toast explaining that the feature is unavailable.
Shareable URLs
Every countdown timer has a URL. Copy it from the Share card, or build your own with these parameters:
| Parameter | Meaning | Example |
|---|---|---|
| ?t=5m | Duration as a short string (h/m/s) | countdown-timer.html?t=5m |
| ?h=1&m=30 | Hours and minutes separately | countdown-timer.html?h=1&m=30 |
| ?s=90 | Total seconds only | countdown-timer.html?s=90 |
| &name=Exam | Pre-fill the timer name | ...?t=45m&name=Exam |
| &auto=1 | Start counting down immediately | ...?t=5m&auto=1 |
Auto-start is useful for QR codes on tables or classroom screens — scan and the timer begins counting down without anyone needing to press a button.
Common use cases
Exam timing
Big screen mode on a projector with a visible countdown.
Cooking
Set for baking, steeping or resting times.
Meetings
Keep stand-ups and timeboxes honest.
Workouts
Intervals, rest periods, circuit training.
Classroom
Group activities and test periods.
Meditation
Focus sessions and breathing exercises.
Privacy
This countdown timer runs entirely in your browser. All timing is computed locally using standard browser APIs. Your durations and timer names are never transmitted, stored or logged — but they are visible in the URL if you share it.