Countdown Timer

Set and run a countdown

Enter hours, minutes, and seconds or choose a preset. Add an optional title, start the timer, and pause or resume as needed. At completion, the chime repeats and the browser tab flashes until you select Stop alert. The first Start may also offer optional browser notifications without delaying the countdown.

Deadline-based countdowns

When started, the timer creates a deadline from the selected duration and the browser's monotonic clock. Each display update subtracts the current timestamp from that deadline. This avoids drift caused by assuming an interval callback arrives exactly once per second.

Worked example

Choose the five-minute preset and start. After two minutes, pausing leaves roughly three minutes. Waiting while paused does not consume that remainder. Resume creates a new deadline three minutes ahead. At zero, the page announces completion, repeatedly chimes, and flashes the tab until Stop alert is selected.

Useful timer titles

A short label such as Tea, Stretch, Presentation, or Oven check makes the completion message and optional browser notification easier to identify. The title stays in the page and is not uploaded. It does not create a calendar event, cloud record, or shareable link.

Hidden tabs and device sleep

Browsers throttle hidden pages, so the visible digits may refresh less often in another tab. Deadline arithmetic catches up when execution resumes. However, a browser can suspend or discard a tab, a laptop can sleep, and a mobile system can stop background work. Use a dedicated alarm or safety-rated timer when missing a deadline could damage property, food, equipment, medication routines, or people.

Privacy and limitations

Duration and title remain local and are not saved after reload. Alert preferences and whether the one-time notification offer was shown are stored locally. On the first Start, the countdown begins before notification permission is requested. Browsers and operating systems can suppress sound or notifications, and this page does not run a service worker, override silent mode, or keep a device awake. Maximum entered hours are limited to 99.

Countdown Timer FAQ

Will the timer survive a reload?

No. Reloading starts a fresh page and clears the active countdown.

Why did the display jump in a hidden tab?

The browser throttled rendering, then the page recalculated from the deadline when it resumed.

Can I rely on it for an oven or medication?

No. Use a dedicated alarm where a missed alert carries meaningful risk.