Online Timer

Why browser timers drift, and why this one does not

Browsers deliberately slow down pages you are not looking at, to save battery. A background tab may run its timers only about once a second, and Chrome batches the repeating timers of a tab hidden for more than five minutes to roughly once a minute. A countdown that works by subtracting a second each time its timer fires therefore falls behind the moment you switch tabs, and can finish minutes late.

This timer never counts. When you press Start it records the moment the countdown should end, and every update simply subtracts the current time from that deadline, so however late an update arrives, the number it shows is right. The alarm is scheduled for the deadline itself, and a small background worker checks the clock every second as a backstop. If the computer sleeps, the timer is still correct when it wakes — and says if it finished while the device was asleep, rather than pretending it rang on time.

The alarm, notifications and phones

The alarm is generated by your browser's own audio engine — four quick beeps a second, like a kitchen timer — so there is no sound file to download, and it is scheduled on the audio clock, which keeps it even in a background tab. It rings for up to two minutes or until you press Stop alarm. Browsers only allow sound after you have interacted with a page; starting the timer counts, and Test sound lets you check the volume first.

Desktop notifications are optional and off until you ask: press 'Notify me when time is up' and your browser asks permission — the page never asks on its own. A notification appears only if the tab is not in front when time runs out. Android browsers only show notifications from sites that install a service worker, which this one does not, so rely on the sound and vibration there; iPhones do not let web pages vibrate at all.

Phones are stricter than computers. Mobile browsers pause or heavily restrict a page when the screen locks or another app comes to the front, so no web timer can promise to ring then. The countdown is still correct when you return, but the alarm will be late. Keep the page open and the screen on — the timer asks the browser to keep the screen awake while it runs, where that is supported — or use your phone's clock app for alarms you cannot afford to miss.

Presets, controls and the tab title

The presets cover the timers people reach for most — 1, 2, 3, 5, 10, 15, 20, 30, 45 and 60 minutes — and start immediately. For anything else, type hours, minutes and seconds; the fields may overflow, so 90 in the minutes box is an hour and a half. The longest timer is 99 hours, 59 minutes and 59 seconds.

+1 min adds a minute to a running or paused timer, and on a finished one starts a fresh minute, as a snooze. Reset returns to the length you set. The tab title shows ⏱ and the time left while running and ⏸ while paused, so you can watch it from another tab. Full screen makes the digits as large as the screen allows, for a classroom, a talk or across a kitchen.

What people use an online timer for

Cooking and baking — eggs, pasta, rising dough. Exams and practice papers, where a large countdown on a projected screen keeps everyone to time. Presentations and speeches with a hard limit. Workouts, planks and stretching intervals. Children's screen time and turn-taking, where an alarm everyone can hear settles arguments. Reminders, such as the parking meter or the laundry. For working in focused blocks, the Pomodoro timer on this site automates the work-and-break cycle.

For a lesson or an exam, open the timer on the projector, press Full screen and choose the time. The digits are readable from the back of a room, and the alarm is loud enough to be heard over conversation at a sensible volume.

Privacy and limits

The timer runs entirely in your browser. Nothing is sent anywhere, there is no account, and closing the tab ends the timer — it is not saved. Changing your computer's clock while a timer runs will shift it, because the deadline is measured against the system clock; the small automatic corrections computers make to their clocks are too small to notice.