Countdown Timer
Create countdown timers with custom time and reminders
Set Time
What is an Online Countdown Timer?
An online countdown timer is a free browser-based tool that counts down from a time you set and alerts you when it hits zero. Set it for a 25-minute Pomodoro session, a 6-minute egg, a 45-minute exam - whatever you need a time limit for. Unlike watching the clock, a timer lets you stop thinking about time and focus entirely on the task. The alarm pulls you back when the countdown ends. No downloads, no sign-ups, nothing uploaded. Everything runs in your browser tab.
How to Use
How to use
- Enter hours, minutes, and seconds - or click a preset time
- Click 'Start' to begin the countdown, 'Pause' to pause
- The display turns yellow near the end and red in the final 10 seconds
- A sound alert plays when the countdown reaches zero
Timing Notes
- Browser timers can pause or drift when the tab is in the background, the device sleeps, or power-saving mode is enabled.
- For meetings, exams, or production work, keep a system clock or dedicated timer as the final reference.
Use Cases
How It Works
The countdown doesn't rely on setInterval to count seconds - that approach drifts over time because the browser's event loop only guarantees a minimum delay, not a steady beat. Instead, the timer records a start time using Date.now() and recalculates the remaining time on every frame: remaining = targetDuration − (Date.now() − startTime). This self-correcting design means the displayed time stays accurate even if the JavaScript thread is briefly busy with garbage collection or layout work.
Display updates are driven by requestAnimationFrame, which syncs to your screen's refresh rate (usually 60 times per second, or 120 on high-refresh-rate displays). The visual update is smooth, but the real timekeeping comes from the Date.now() calculation - the animation is just for display, not for measurement.
When the tab goes into the background, browsers throttle timers aggressively. Hidden tabs can have setInterval clamped to one call per second, and inactive tabs may be frozen entirely after a few minutes on battery power. The timer handles this by checking the system clock as soon as the tab becomes visible again, jumping the display to the correct remaining time. For the finish-line alarm, the page uses the Web Audio API to play a short tone. This requires a one-time user interaction (like clicking Start) before audio is allowed - a browser autoplay policy that prevents unwanted sound. If the tab is hidden or the system is asleep, the alarm won't fire, but the display will show the correct elapsed time as soon as you return.
- Uses Date.now() for wall-clock accuracy - recalculates remaining time on every frame instead of counting setInterval ticks.
- requestAnimationFrame syncs display updates to your screen's refresh rate for smooth rendering.
- Background tabs are throttled by the browser; the timer reconciles using the system clock when you return.
- Web Audio API plays the alarm and requires a user gesture (like clicking Start) before audio is allowed.
- All computation runs locally in the browser. No data is sent anywhere.
Examples
Pomodoro work block (25 min focus + 5 min break)
Duration : 00 : 25 : 00
Start at : 14:00:00
Finish at : 14:25:00 (alarm plays)
Next : 5-minute break timer (preset)Cooking - soft-boil egg (6 min 30 s)
Set : 00 : 06 : 30
At 1:00 -> visual warning highlights remaining time
At 0:00 -> alarm + page banner: Countdown Complete!Exam invigilation - 45-minute writing block
Duration : 00 : 45 : 00
Start : 09:15:00
End : 10:00:00
Tip: leave the tab in foreground - background tabs may throttle setInterval and drift by several seconds over 45 minutes.FAQ
Does the countdown keep running if I switch tabs?
Yes. The timer uses your system clock to track elapsed time, not animation ticks. When you switch back, the display jumps to the correct remaining time immediately.
Will the alarm sound if the tab is in the background?
It depends on your browser and device. Some browsers restrict audio in background tabs to save power. If the alarm matters, keep the timer tab visible or in its own window.
What happens if my computer goes to sleep?
The timer tracks time using your system clock, so it stays accurate through sleep. The display catches up when you wake the computer. But the alarm won't sound while the system is suspended.
How accurate is the countdown?
The display updates every second, but internally it uses millisecond-precision timestamps. For everyday use - cooking, meetings, workouts - it's more than accurate enough. Background tabs may lose some precision due to browser throttling.
Can I save my timer presets?
Quick preset buttons for 5, 10, 25, and 45 minutes are built in. For other durations, type the time directly into the hours, minutes, and seconds fields.
Does daylight saving time affect the countdown?
No. The timer counts elapsed seconds, not calendar time. A 2-hour countdown always lasts exactly 2 hours, regardless of DST changes.
Is any data sent to a server?
No. The timer runs entirely in your browser. Timer data never leaves your device.