ARTICLE · 11 SEPTEMBER 2026

The 20-20-20 rule: a 20 minute timer for tired eyes

Every 20 minutes, look at something 20 feet away for 20 seconds. It is the advice most often given to people who work at a screen. Where the numbers come from, how strong the evidence is, why almost everyone who knows the rule fails to keep it, and how to turn it into a habit.

Three twenties

The rule: after 20 minutes of screen time, spend 20 seconds looking at something at least 20 feet (about six metres) away. It was popularised in the 1990s by the American optometrist Jeffrey Anshel, who gave it to his patients as an easy thing to remember, and it has since been adopted by bodies such as the American Academy of Ophthalmology as standard advice for screen workers.

Of the three numbers, the first two are the ones that matter. Twenty feet is simply a memorable way of saying "far": out of a window or down a corridor, anywhere the eye can focus at distance. Twenty seconds is roughly the minimum for an eye held at near focus to relax. And twenty minutes, as the rest of this article explains, is the number people find hardest to keep.

What a screen does to your eyes

Two things happen at once.

The focusing muscle stays tenseSeeing something close requires a muscle inside the eye to thicken the lens. A monitor sits 50 to 70 cm away, and holding that distance for hours keeps the muscle working continuously. Looking into the distance lets it go. That is what the 20 seconds are for.
You blink lessPeople normally blink 15 to 20 times a minute. Several studies have found that concentrating on a screen cuts that by half or more. Fewer blinks means the tear film dries out, which is the gritty, red-eyed feeling by evening.

The combined symptoms are called computer vision syndrome or digital eye strain: blurring, dryness, headaches, and often neck and shoulder pain alongside. The 20-20-20 rule targets the first cause directly, and because people blink naturally while looking away, it touches the second a little too.

How strong is the evidence

To be honest about it: there is no large trial behind the exact numbers 20-20-20. The rule is a memorable prescription from clinical experience, not a value optimised by experiment. Thirty seconds every 25 minutes would probably do just as well.

There is research supporting the direction. In 2023 a team at Aston University in the UK used software to make computer users follow the rule for two weeks and found that eye-strain symptoms and dryness decreased. The interesting part is that once the software was switched off, the benefit disappeared. Not because the rule was wrong, but because people stopped following it.

Why everyone knows it and nobody keeps it

Almost nobody hears this rule for the first time. Almost nobody keeps it either. There are three reasons.

20 minutes is invisible while you are absorbedWhen you are concentrating, 20 minutes passes like five. Checking the clock does not occur to you, so the 20 minutes go by no matter how well you remember the rule. Left to your sense of time, it fails every time.
Reminders get dismissedA pop-up every 20 minutes is being closed reflexively by day three. The moment reminders feel like interruptions they get switched off, and the rule goes with them.
20 seconds feels longLooking out of a window, 20 seconds is longer than it sounds. People look for about five and turn back, before the focusing muscle has let go. The 20 seconds need counting too.

What the three have in common is that nothing shows the time. Neither the 20 minutes that have passed nor the 20 seconds of rest are visible. A reminder arrives once, at the end, and gets dismissed.

Keep the countdown in view

Replace the reminder with a countdown that is always visible and all three problems shrink at once. With the minutes remaining sitting in the corner of the screen you do not rely on your sense of time; nothing pops up to be dismissed; and the 20 seconds of rest can be counted in the same window.

Set the focus cycle to 20/1
Open the focus cycle and in settings change focus to 20 minutes, the short break to 1 minute and the long break to 5. Switch on auto-start. Spend 20 seconds of each one-minute break looking into the distance and the rest blinking or drinking water.
Press PiP
The timer detaches into a small window above your document or editor. A corner keeps it in view without covering the work.
Leave the completion sound on
When you are deep in something you stop seeing the window. The sound is the last safety net.
Bookmark the settings link
Use the copy-settings-link button and bookmark the address. Each morning is then one click and a press of start.

A plain 20 minute timer works too. It has to be restarted each time, though, so for a whole day the cycle is the better tool.

Alongside the rule

Monitor heightThe top of the screen should be at or slightly below eye level. A slightly downward gaze keeps more of the eye covered by the lid, which slows drying.
DistanceAbout an arm's length, 50 to 70 cm. Laptops drift closer than that without anyone noticing.
BrightnessA screen much brighter or darker than the room forces constant adjustment. Match it to the room and avoid sitting with a window behind you.
Blink deliberatelyClosing the eyes firmly a few times during a break restores the tear film. It looks silly and it works.