Online timer

How it keeps exact time

Many web timers count down by adding up one-second ticks. Browsers slow those ticks down in background tabs and on phones to save battery, so the timer drifts and the alarm goes off late. This timer instead notes the exact moment it should finish when you press Start, and on every update it shows the difference between that moment and the clock. A slow or skipped update changes nothing: as soon as the page draws again, the time is right.

The alarm is made with the browser's Web Audio feature (a generated beep, no sound file). When you press Start it is booked on the audio system's own clock for the finishing moment, so it rings on time even if you are in another tab. Your device must not be muted, and some phones stop all sound when the screen locks, so keep the screen on for anything important.

• Countdown: shows the time left rounded up to the whole second, so 0:00 appears only when time is really up. +1 minute adds time without stopping.
• Stopwatch: shows hundredths of a second. Lap records the time since the last lap and the total; with two or more laps the fastest and slowest are marked.
• Pomodoro: alternates focus blocks and breaks, with a longer break after every few focus blocks. Each block starts at the planned end of the last one, so the schedule does not creep.

Worked example: a Pomodoro session

With the classic settings (25-minute focus, 5-minute short break, 15-minute long break after every 4 focus blocks), one full cycle is 4 × 25 + 3 × 5 + 15 = 130 minutes: Focus 1, short break, Focus 2, short break, Focus 3, short break, Focus 4, long break. Start at 9:00 and Focus 1 ends at 9:25, Focus 2 runs 9:30–9:55, Focus 3 10:00–10:25, Focus 4 10:30–10:55, and the long break ends at 11:10, ready for the next cycle.

Classroom and meeting tips

• Press Full screen to show just the time in large digits on a projector or shared screen.
• The time left also shows in the browser tab's title, so you can see it while working in another tab.
• Share a ready-made timer with a link: add ?m=10 to this page's address for 10 minutes, or ?t=7m30s for 7 minutes 30 seconds. Opening the link sets the timer; press Start to run it (browsers only allow sound after you press a button).
• Pair it with the wheel spinner to pick who presents next.