20 Minute Timer

The nap timer, and why the alarm matters more than the countdown

The twenty-minute nap is the best-known use of this length, and it is also the case where a browser timer is most likely to let somebody down. Every other use on this site involves watching a screen. A nap involves deliberately not watching one — usually with the phone face down, the laptop lid nearly shut and the tab pushed to the background behind whatever you were working on.

That is exactly the situation in which most web timers quietly fail. A hidden tab has its scripts throttled, so a countdown that plays its sound from JavaScript when it notices it has finished can notice late. This page books the alarm on the browser's audio clock at the moment you press start, so the sound is scheduled before the tab is hidden and does not wait on a throttled script.

Twenty minutes is also the length at which we have to stop selling that and start qualifying it, because this is the page where the qualification actually bites. The exemption browsers grant to audio is an exemption for audio that is audible, and a timer counting down to a beep is silent for the entire wait. A silent context is one a browser may suspend outright when the tab is hidden, and while it is suspended the audio clock does not advance. Worse, the strictest tier of script throttling in Chrome applies to a tab that has been hidden and silent for more than five minutes — the same condition — so on a twenty-minute nap the fallback and the audio path are degraded together. In practice that means the beeps are deferred, not lost: they tend to arrive when you come back to the tab. That is a fine outcome for an eye break and a useless one for a nap you actually needed to end at twenty minutes.

So: if the consequence of oversleeping is serious — a train, an interview, a shift — use a phone alarm, and if you want the best chance from this page, keep the tab visible on a second screen where your own work cannot bury it. A closed laptop or a dead battery ends any web page, and no amount of careful scheduling survives that. What the page does still guarantee is the number: the countdown is derived from a fixed end instant, so however long the tab was hidden, the time it shows when you look at it is correct.

Twenty minutes away from the screen

The other twenty-minute habit is the eye break: a widely repeated guideline for screen work suggests looking away from the display every twenty minutes, at something roughly twenty feet away, for about twenty seconds. We have not evaluated the evidence behind it and are not going to claim an effect for it — what we can say is that it is a rule you cannot follow without a reminder, because the entire failure mode is not noticing that twenty minutes have gone.

Used that way the timer runs in a background tab all day, which puts the accuracy question front and centre. Three twenty-minute cycles fill an hour; a working day is twenty-four of them. Projected from the rate we measured, a naive tick-counting timer would finish each cycle about 14 s late on a busy page, so the twenty-fourth break of the day arrives 327 s after it should. A drifting reminder is a reminder that slowly stops being about twenty minutes. The runs those rates came from are published on the online countdown timer home page.

The same length works for a soak, a marinade, a laundry cycle checkpoint, a focused tidy of one room, and the first block of a study session before a proper break. For a longer block the 30 minute timer is the next step up; for the structured version with breaks built in, use the Pomodoro timer.

Setting a twenty-minute timer you can trust

Test the alarm before you rely on it. Press Start, listen for the tones, then press Reset. Ten seconds of checking is worth more than any promise a web page can make about its own audio.

Leave the tab open, not just the browser. Closing the tab ends the timer completely; switching to another tab or another application is fine. On a laptop, sleep ends it too — the page is not running while the machine is not.

Full screen is for naps as well as classrooms. A full-screen countdown on a second monitor is readable from a couch without unlocking anything, and it stops the browser from being a tempting thing to scroll while you are meant to be resting.

Use the URL if this is a routine. Bookmark this page for twenty minutes flat, or build your own: ?t=25m, ?t=20:00 and ?t=1200 all work on any page of the site.

The numbers behind a 20 minutes timer

Every row here is worked out from the duration itself: the conversions are arithmetic on 1,200 seconds, and the accuracy rows come from the drift measurement described on the home page. The source column says which is which.

One disclosure belongs beside the table itself, where you will actually read it: those drift figures were measured in Node v22.20.0 on one Windows desktop, not in a browser (win32 10.0.26200, AMD Ryzen 9 9950X3D 16-Core Processor, on 2026-08-14). Each condition was run 5 times and the figures used here are the medians, because single runs of this kind vary by more than the difference they are being used to describe. Your machine will produce different numbers. What transfers is the shape — a counter that accumulates drifts, and a counter that subtracts from a fixed instant does not.

Start now, finish when?

The most common question about any fixed-length timer is what time it lets you out. These finish times are computed at build time from the start time plus 1,200 seconds, so the rows that cross midnight are right for the same reason the rest are.