Countdown Timer

Set a timer

Type a duration or tap one of the presets, press Start, and get an alarm at zero. The bar under the clock shows how far through you are, which the numbers alone do not — 08:41 tells you nothing about whether that is nearly done.

Everything runs in your browser. Nothing is uploaded, and the duration lives in the page address so you can bookmark a timer you use often.

The problem with most online timers

They lose time when you look away, and they do it silently.

The usual way to build a timer is to run something once a second and add a second to a running total each time. In a tab you are looking at, this works perfectly. It is also what every developer tests, because testing means watching.

Then the visitor switches tabs — and browsers deliberately throttle background pages to save battery. First to once a second, then to once a minute, and on a phone with the screen off, often not at all. A timer built that way simply stops counting. You come back after twenty-five minutes of focus and it reads nine.

There is no error, nothing on screen looks wrong, and the number is confidently incorrect.

How this one works instead

It stores when you started, not how much has passed.

Time remaining is then a subtraction against whatever the clock says right now, so it does not matter whether the last update was sixteen milliseconds ago or four minutes ago. The repeating update stops being the source of truth and becomes what it should always have been: something that redraws the screen.

The practical effect is that the display can freeze while a tab is hidden, and the number is still right the moment you look back. Nothing accumulates, so nothing drifts.

And the alarm

Keeping the display honest is only half of it. Something still has to happen at zero, and a JavaScript timeout in a hidden tab is exactly the thing browsers delay. An alarm that goes off whenever you next glance at the tab is not an alarm.

So the sound is scheduled on the audio hardware’s own clock the moment you press Start. That clock runs in the audio thread and is not throttled — it is the same mechanism that lets music keep playing in a background tab. The whole alarm is booked in advance and cancelled if you pause.

One consequence worth knowing: because the sound is armed by your press of Start, ticking the alarm box after starting re-arms it, and browsers will not let any page make a noise before you have interacted with it at all.

What it cannot do

Two honest limits.

Closing the tab stops it. Everything here runs in the page. Leaving the tab open in the background is exactly what the tool is designed for; closing it is the end of the timer. Nothing runs on a server, and nothing is left behind.

A locked phone is up to the phone. Ticking Keep the screen on asks the browser for a screen wake lock, which stops the display sleeping while the timer runs. Support is patchy, the lock is released whenever you leave the page, and the tool re-requests it when you come back. If the phone sleeps anyway, the timer still keeps correct time — you just may not hear it until you wake the device.

Why the clock rounds up

Start a five-minute timer and it reads 5:00, not 4:59.

That is deliberate. The reading is the number of seconds you still have, rounded up. A timer that truncates instead drops to 4:59 the instant you press Start — before a second has passed — and then sits on 0:00 for a full second while you wait for the alarm. Both look like bugs, and both are what you get from the obvious implementation.

It also means the last second of the countdown is a real second, which matters if you are using the timer to time anything.

What people use a timer for

The presets are the durations that actually get set, which is a shorter list than you would guess.

1–3 minutes — tea, a plank, a breathing exercise, a pitch.
5–10 minutes — eggs, a warm-up, a stand-up meeting, a break.
15–25 minutes — a focus block, a nap, a rest between sets.
45–60 minutes — a lesson, a laundry cycle, a parking meter.

For repeated focus blocks with breaks between them, the pomodoro timer tracks the cycle for you rather than making you restart this one. To measure how long something took rather than count down to it, use the stopwatch.

Using it with a screen reader

A ticking clock is a genuine accessibility problem: a live region that announced every second would make the page unusable, and one that never announced anything would leave you with no idea the timer was running.

So the reading itself is silent and readable on demand, and the timer speaks at milestones — every minute under five, every ten seconds under one, then each of the last ten seconds, and once at zero. The spoken form says its units (“four minutes fifty-seven seconds”) rather than reading out a clock face, which some screen readers pronounce as a list of digits.

Frequently asked questions

Does the timer keep running if I switch tabs?

Yes, and it stays accurate. Browsers throttle background timers heavily — often to once a minute — so this works out the time from the moment you pressed Start rather than by counting ticks. The display may pause while the tab is hidden, but the number is correct the instant you look again.

Will the alarm still sound in a background tab?

Yes. The sound is queued on the audio hardware's own clock the moment you press Start, and that clock is not throttled. Most timers schedule the alarm with a JavaScript timeout, which is exactly the thing a hidden tab delays.

Why is there no sound?

Browsers refuse to play audio until you have interacted with the page, so the alarm is armed by your press of Start. If you started the timer, left the tab, and came back to silence, check that the Sound an alarm box is ticked and that the tab is not muted.

Can I close the tab and still get the alarm?

No. Everything here runs in the page, so closing the tab stops it entirely. Leaving the tab open in the background is fine — that is what the tool is built for — but the page has to exist.

Will my phone screen turn off?

It will, unless you tick Keep the screen on, which asks the browser for a screen wake lock. Support varies and the lock is released whenever you leave the page, so the tool re-requests it when you come back. The timer itself keeps time either way.

Can I share or bookmark a timer?

Yes. The duration and the settings are in the page address, so a link opens the timer already set. It does not start on its own — that would be a page that makes a noise at you without asking.

Why does it show 5:00 for a moment after starting?

The reading is rounded up, so it shows the number of seconds you still have. A timer that truncates displays 4:59 the instant you start a five-minute countdown, and sits on 0:00 for a full second before the alarm.