Countdown Timer
00:00
The countdown timer counts down from any duration up to three hours. It tracks a fixed end time rather than decrementing a counter, which is what keeps it accurate when a browser throttles a background tab, the usual reason a web timer finishes late.
How it works
Browsers deliberately slow timers in inactive tabs, often to once per second or less, to save battery. A timer that subtracts a fixed amount on each tick therefore falls behind by however long the tab was in the background.
- The end time is calculated once when you press start.
- Each tick recalculates the remaining time from the current clock rather than subtracting from a counter.
- When the tab returns to the foreground the display corrects itself immediately instead of finishing late.
No sound is played when the timer ends. Browsers block audio that a user did not directly trigger, so an alarm would fail silently in exactly the situation where it matters most, a backgrounded tab.
Examples
A five-minute timer
Minutes
5
Seconds
0
Result
Counts down from 05:00 to 00:00
Switching tabs during the countdown does not slow it. The display corrects on return rather than drifting.
A short interval
Minutes
0
Seconds
90
Result
Accepts 90 seconds and displays it as 01:30
Seconds above 59 are not rejected, they roll into minutes, which is quicker than converting by hand.
Frequently asked questions
Why does the timer not play a sound when it finishes?
Because browsers block audio that a user did not directly trigger, and a backgrounded tab is exactly where that block applies. A timer that appears to have an alarm and then fails silently is worse than one that never claimed to, so it does not claim to.
Does it keep time accurately if I switch tabs?
Yes. It tracks a fixed end timestamp rather than counting down a variable, so throttling changes only how often the display refreshes, not when the timer ends. Timers built the other way finish late by however long the tab was hidden.
What happens if I reload the page?
The timer is lost. Nothing is stored, so a refresh starts over. For anything you cannot afford to lose, a phone timer survives a browser crash and this does not.
Can I enter more than 59 seconds?
Yes. 90 seconds is accepted and displays as 01:30. There is no reason to force the conversion when the arithmetic is trivial.