Countdown Timer

Pasta that needs 11 minutes, a 45-minute practice exam, a 90-second plank: type the length or tap a preset of 1, 5, 10, 15, 25 or 30 minutes and press Start. The fields take any whole numbers, so 90 in Minutes is read as 01:30:00, and 100 in Seconds as 00:01:40. From the site search, typing timer 10m or timer 1h 30m 20s opens the timer already running. A link that ends in ?duration=10m&auto=true does the same, so a teacher can put one link on the board and every student's timer starts at 10:00.

This is a timer for a length of time. To count the days to a date, such as a deadline or a holiday, use the Days Until Countdown, which counts to a calendar date instead.

The end is silent unless you turn on Sound at the end, which plays three short beeps made by your browser. While you work in another tab, that tab's title shows the time left.

Pressing Start fixes an end time: end = now + length. About ten times a second the page compares the clock with that end time and shows the difference, rounded up to a whole second, so the display reads 00:00:01 until the time is really over. Nothing depends on counting ticks, so the time shown is the real time left whenever you look. Pausing stores the exact time remaining and resuming sets a new end time from it.

The length is hours × 3,600 + minutes × 60 + seconds. Entering 1 hour, 75 minutes and 90 seconds gives 02:16:30. The shortest timer is 1 second and the longest is 7 days (168:00:00).

Limits: the timer lives in the open page, so closing or reloading the tab ends it, and there are no system notifications. Browsers slow down the timers of hidden pages, so a background worker keeps checking the clock, and with the sound on the end beeps are placed on the browser's audio clock ahead of time; in a background tab they normally sound on time. A browser that suspends the tab or its audio, for example when a phone's screen locks or a battery saver is on, can still delay or silence them. The end time follows the device's clock, so changing that clock during a run moves it. Do not rely on this timer where a missed alarm matters.