Screen break timer: a 20-20-20 reminder

How to use it

Press start and the timer counts down from 20:00 to your next break. You can switch tabs and keep working, but leave this tab open: closing it, or the browser, stops the timer.

When it reaches zero, look at something about 20 feet (6 meters) away or farther: a view from a window, the far end of an office, a long corridor. Rest your eyes there while the timer counts off 20 seconds, and blink fully a few times. Then go back to work; the next 20 minutes have already started.

The soft sound is optional. Turn it on if you tend to miss the change on screen, especially with the tab in the background.

Nothing is stored or sent. The timer runs entirely in your browser tab and keeps no record of your breaks.

The breaks help most when the rest of your setup is kind to your eyes as well:

• Keep a computer screen at about arm's length, roughly 50 to 70 cm (20 to 28 inches). Hold a phone a little farther away than feels natural, and make text larger rather than leaning in.
• Set the screen so its center sits a little below eye level and you look slightly down. Your eyelids then cover more of the eye's surface, so tears evaporate more slowly than when you gaze up at a high monitor.
• Put the screen side-on to windows, and match its brightness to the room so it neither glows nor looks dim.
• People blink less often, and less completely, while they concentrate on a screen. Use each break for a few slow, full blinks, letting the lids close all the way.
• Heating and air conditioning dry indoor air. Turn vents and fans away from your face, and raise the humidity in very dry rooms. In a Kyoto winter, with heaters running all day against the basin cold, indoor air dries out fast.

If a laptop or a low monitor keeps your head tipped down, a stand that lifts the screen is the simplest fix, and a humidifier helps in a room that dries out overnight.

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How the numbers work

When you press start, the timer notes the clock time. From then on it works out the time left from the clock, not by counting ticks:

time to next break = period - (time since start mod period)

The period is 20 minutes (1,200,000 milliseconds), and "mod" means the remainder after taking away whole periods. The result is shown in minutes and seconds, rounded up to a whole second. The defaults are a break every 20 minutes, a 20-second look, and a distance of 20 feet.

A worked example: you press start at 9:00:00, and at 9:47:15 you glance at the tab. The time since start is 47 minutes 15 seconds. Two whole periods (40 minutes) have passed, leaving 7:15. Then 20:00 minus 7:15 is 12:45, so the display reads 12:45 and the next break comes at 10:00:00.

Because the countdown is calculated from the start time, it does not drift. If your computer sleeps or the browser slows a background tab, the display jumps to the right point in the cycle when you come back, although a reminder can arrive a little late.

The 20 feet has a reason in optics. The effort your eyes put into focusing, measured in diopters, is 1 divided by the distance in meters. A screen at 50 cm asks for 2 diopters. An object 6 meters away asks for about 0.17, close to the zero needed for the horizon, so the focusing muscle inside the eye can almost fully relax. Twenty seconds is a pause long enough for that and a few blinks, short enough not to break your concentration.

What this tool can't tell you

This is a reminder, not a test or a treatment. Regular breaks can ease the tired, heavy feeling of long hours of close focus, and they remind you to blink. That is about all they do.

The habit does not prevent nearsightedness on its own. For children, the stronger evidence is for time outdoors: studies suggest around 2 hours a day outside helps reduce the chance of becoming nearsighted, and the column on myopia and outdoor time explains more. Nor does it treat dry eye disease, a condition where the tear film no longer keeps the surface of the eye healthy, which needs an eye doctor's assessment. The column on dry eyes and screen time covers tears, drops and humidity in more depth. Breaks also cannot fix blur from glasses you need but do not have, or from reading glasses that are no longer strong enough.

See an eye doctor if your eyes stay dry, gritty, burning or red despite good habits, if blur does not clear when you blink, or if you get regular headaches, double vision or have to squint and lean in to read. An optometrist can test if you need glasses or a new prescription; an ophthalmologist, a medical doctor who specializes in eyes, treats eye disease. If work makes appointments hard to fit in, see the guide to eye care around a working week. Contact lens wearers with pain, redness, light sensitivity or blurred vision should take the lenses out and see an eye doctor the same day.

Some symptoms are urgent whatever you were doing. Sudden severe eye pain with blurred vision, halos around lights, headache and nausea is an emergency. So is sudden loss of vision in one eye, even if it returns within minutes, which can be a warning sign of stroke. New flashes, a sudden shower of floaters, or a shadow like a curtain across part of your vision need same-day eye care. For an emergency, call your local emergency number (such as 911, 999, 112, or 119 in Japan).

Questions people ask

Does 20-20-20 stop children becoming nearsighted?

Not on its own. Breaks and a sensible screen distance are good habits, but the evidence points most clearly to time spent outdoors in daylight. If a child holds screens very close, squints or complains of blur, book an eye check.

What if there is nothing 20 feet away?

Look down the longest line of sight you have, such as a hallway. Closing your eyes for the 20 seconds also gives them a rest. Walking to a window is better still.

Will the timer keep going if I lock my screen?

The countdown is worked out from the time you pressed start, so it picks up at the right point when you come back. As long as the tab stays open, nothing needs to be restarted.

Should I take longer breaks too?

Many workplaces advise getting up from screen work every hour or so. Check your employer's guidance on screen use, and treat the 20-second pause as a small addition, not a replacement.

Sources

• American Academy of Ophthalmology patient pages on computer use, eye strain and dry eye.
• American Optometric Association guidance on digital eye strain (screen distance, screen height and the 20-20-20 habit).
• TFOS DEWS II report (2017), for the definition of dry eye disease.
• International Myopia Institute reports on myopia and time outdoors.