Online Timer and Countdown

How to use the online timer and countdown

1. Enter hours, minutes and seconds, or press a preset such as 5 min. Add an optional label like Tea or Meeting.
2. Press Start. The large display counts down and the browser tab title shows the time left, so you can see it from another tab.
3. Use Pause and Resume at any time, or Reset to go back to the full duration.
4. When the time is up you see a completion message and hear an alarm. Press Stop alarm to silence it. Use Test sound and the volume slider beforehand, or tick Mute alarm.
5. For a deadline, choose Count down to a time or date, pick the moment, and press Start.

Worked example

Accurate in background tabs

The countdown does not subtract one second every time a timer fires. It stores the moment it should end, and whenever it needs to draw it computes the end moment minus the current clock reading. If the browser slows this tab down because you are looking at another one, the screen may update less often, but the remaining time is still exact whenever it is drawn.

A check also runs when you return to the tab, and a wake-up is scheduled for the exact end time. Browsers can still delay a wake-up in a hidden tab, sometimes by up to a minute when a tab has been hidden for a long time. So in a background tab the alarm may sound a little late, but the time shown is never wrong. If a precise alarm matters, keep the tab visible or in its own window.

The alarm sound

The alarm is a tone generated in your browser with the Web Audio system. No audio file is downloaded. Browsers do not allow a page to play sound until you interact with it, so the audio system is switched on when you press Start. Nothing ever plays when the page first loads, and Test sound plays a short sample at the current volume.

The completion message is always shown as text and announced to screen readers, so the timer works with the sound muted or the volume turned down. The page title changes to a time-is-up message as well.

Counting down to a time or date

In the second mode you choose a date and time in your own time zone, and the timer counts the real time between now and then, up to 99 hours 59 minutes 59 seconds. It converts your target into a duration when you press Start, so the countdown keeps running from the browser clock. If you change the device date or time zone afterward, restart the timer. A moment in the past is rejected with a message.

What the page remembers

The last duration you started is stored in this browser with localStorage so it is ready next time. That is the only thing saved, it never leaves your device, and clearing site data removes it. Labels are not stored.

Assumptions and limits

• The longest timer is 99 hours, 59 minutes and 59 seconds. The shortest is one second.
• The page must stay open. Closing or reloading the tab stops the timer.
• Alarms are generated sounds. If your device is on silent or the browser tab is muted, you will only see the message.
• In a hidden tab the browser may delay the alarm by up to about a minute. The time shown is still correct.
• Countdown to a date uses your device clock and time zone. It does not adjust for a clock that is set wrongly.

Formulas reviewed October 10, 2026. See the calculation methodology for how SumPanda rounds, tests and sources its formulas.

Frequently asked questions