Online Timer
Set hours, minutes and seconds (or tap a quick-set button), hit Start, and get a huge countdown with an audible alarm at zero -- accurate even if you switch tabs.
Keyboard: Space start/pause, R reset, Esc stop alarm.
How it stays accurate in a background tab
Most homemade timers count down by subtracting one second, once a second, from a number in memory -- which works fine until the browser throttles or fully suspends a background tab to save battery, a behavior every major browser applies aggressively to timers you can't see. Miss enough of those one-second ticks and the timer drifts behind real time, sometimes by minutes.
This timer never counts ticks. The instant you press Start, it records one number: the exact millisecond timestamp the countdown should reach zero. Every time the display updates -- as often as your screen can redraw while the tab is visible, and at a coarser once-a-second pace while it's hidden -- it simply subtracts the current time from that target and shows whatever is left. A tick that never ran while the tab was backgrounded costs nothing, because the next tick that does run still does the subtraction fresh. Pausing works the same way: it freezes the remaining duration, and resuming recomputes a brand-new target from the moment you resume, not from whenever you happened to pause.
remaining = target end time − current time
Why the alarm is synthesized, not a sound file
The chime, beep and bell tones are generated live with the Web Audio API -- a handful of oscillators and volume envelopes, computed the instant the timer hits zero. That means no audio file to download, nothing for an ad blocker or slow connection to interfere with, and no licensing question about a sound clip. Each tone repeats on its own every couple of seconds until you stop it (with the Escape key, the Stop alarm button, or by starting a new timer), so it won't go unnoticed if you've stepped away.
Common durations, converted
A quick reference for how the durations behind the quick-set buttons compare in other units -- generated from the same engine that runs the countdown above, not typed in separately.
| Duration | In words | Fraction of an hour |
|---|---|---|
| 01:00 | 1 minute | 1/60 hr |
| 05:00 | 5 minutes | 1/12 hr |
| 10:00 | 10 minutes | 1/6 hr |
| 15:00 | 15 minutes | 1/4 hr |
| 30:00 | 30 minutes | 1/2 hr |
| 1:00:00 | 1 hour | 1 hr |
This page's own default duration (10:00) is also what loads if you open the site with no ?t= parameter in the URL at all.
Frequently Asked Questions
Does this timer keep counting if I switch to another tab?
Yes. Instead of counting down second by second, it stores the exact moment the timer should end and recalculates the time left every time the page updates -- including the moment you switch back to the tab. A browser throttling or fully pausing a background tab for ten minutes doesn't cost you any accuracy; the next update still lands on the exact right number.
Where does the alarm sound come from?
It's synthesized in your browser with the Web Audio API -- three tones (chime, beep, bell), each built from a couple of oscillators, no audio file downloaded or blocked by an ad blocker. Pick a tone and mute it from the Alarm controls under the timer; your choice is remembered for next time.
Can I get a browser notification when the timer ends, not just a sound?
Yes -- check "Browser notification" under the timer and your browser will ask for permission once. Nothing is requested until you opt in, and if you decline or your browser blocks it, the audible alarm still fires either way.
Can I share a timer with someone else?
Yes -- setting a duration updates the page's URL with a ?t= parameter holding the number of seconds, so copying the address bar link and sending it to someone opens the same duration, ready to start, on their screen.
What are the keyboard shortcuts?
Space starts or pauses the timer, R resets it, and Escape stops the alarm once it's going off -- all without touching the mouse, as long as focus isn't in a text field.
Is there a limit to how long a timer can run?
Up to 99 hours, 59 minutes and 59 seconds in one setting -- far beyond what a countdown-style timer is normally used for. For counting down to a specific date rather than a plain duration, use the Countdown Timer instead.
Every timer here runs entirely in your browser -- nothing you set is sent anywhere. The countdown display isn't a substitute for a certified stopwatch or a safety-critical timing device; see the Terms.