Online Timer and Stopwatch: Countdown, Alarm, Laps

About the Online Timer and Stopwatch

The Online Timer and Stopwatch puts the two clocks people reach for most on one page. The countdown timer counts down from any time you choose, from one second up to 99 hours, 59 minutes and 59 seconds, and sounds an alarm when it reaches zero. The stopwatch counts up to the hundredth of a second and records laps with their lap and split times. Switch between the two with the Mode control at the top; each clock keeps its own time, so a countdown carries on while you time something with the stopwatch.

Use it for cooking, workouts and interval training, study sessions, presentations, board games, exams or anything else that needs a reliable clock in a browser tab. There is nothing to install and no account to create.

How to use the timer

Why the timer stays accurate in a background tab

Browsers slow down the timers of pages you are not looking at, sometimes to one tick per second or less. A clock that adds a fixed step on every tick therefore falls behind. This tool never counts ticks. When you press Start it records a timestamp from the browser's monotonic clock, and every time the display updates it works the time out again from that timestamp:

$$t_{\text{remaining}} = T - \left( t_{\text{run before pause}} + t_{\text{now}} - t_{\text{start}} \right)$$

Here $T$ is the time you set. Because the result depends only on clock readings, a tab that wakes after ten minutes shows exactly ten minutes less, not the handful of ticks it happened to receive. The tab title also shows the remaining time, so you can glance at it from another tab.

Choosing between the countdown and the stopwatch

• Use the countdown when you know how long something should take: steeping tea, a plank, a 25-minute focus block, a speaking slot.
• Use the stopwatch when you want to find out how long something takes: a run, a lap of a track, a recipe step, a phone call or a puzzle.

For a dedicated page with presets and more countdown tips, open the Countdown Timer. For lap timing in depth, see the Online Stopwatch.

Privacy

Nothing is uploaded; every calculation runs in your browser and never leaves your device. The times and laps live only on this page and disappear when you close or reload it.

Related tools

Add up the hours you worked with the Hours Calculator, convert seconds to minutes or hours with the Time Converter, and count the days between two dates with the Date Calculator.

Frequently asked questions