Countdown timer
Runs in your browser · keep this tab visible
Pick a length, press start, and it chimes at zero. Presets cover one, three, five, ten, fifteen, thirty, forty-five and sixty minutes, and the slider goes up to two hours. Pause holds the remaining time and resume picks it up where it stopped.
How to use the countdown timer
The timing is read from a monotonic clock each frame instead of being counted up one second per interval tick. That distinction is invisible for two minutes and obvious over an hour: interval ticks are only approximately on time and their error accumulates, so a naively built timer runs minutes late. Reading the clock directly means the display is right the instant you look at it, even after the tab has spent an hour in the background.
The chime is the part that can still let you down. A backgrounded tab gets its timers throttled, so the sound can arrive late even while the number on screen is correct, and a device that goes to sleep suspends the browser and skips the chime altogether. Keep the tab where you can see it and the machine awake if the sound is the part you are relying on.
This page counts a length and nothing else. For a moment on the clock, the online alarm clock takes a time of day and watches for it, so there is no arithmetic to do in your head.
What people use it for
- Timing something in the kitchen without picking up a phone
- Boxing a task into a fixed stretch of minutes
- Keeping a meeting item or a presentation to its slot
- Holding a break to the length you said it would be
- Putting a visible clock on a quiz round or a game turn
Questions
No. The remaining time is calculated from a monotonic clock rather than by counting interval ticks, which is where drift comes from.
The number stays correct, but browsers throttle background tabs, so the chime may be late by a few seconds. Keep the tab visible if that matters.
Yes. Pause keeps the remaining time and resume carries on from there.
Not on this page, and you do not have to work out the gap yourself: the online alarm clock takes a time of day and watches the clock for it.
No. Closing the tab ends the page, and nothing can run after that. Keep it open.
No. A locked or sleeping phone suspends the browser. Use the phone’s own alarm app for anything you must not miss.
On a phone, generally not, for the same reason. On a desktop that stays awake, yes.
Yes, there is a mute box. The display still shows when it finishes.
Not on this page: one count at a time.
No. Nothing is stored, so a reload starts fresh.
A monotonic clock in your browser, which only ever moves forward. It is unaffected by the system clock being adjusted mid-count.
Two hours from the slider. For anything longer, the Pomodoro timer or a repeated count is the practical answer.