Online Countdown Timer
Set a countdown in hours, minutes and seconds and run up to five named timers side by side with a beeping, chiming or buzzing alarm. Enter the duration, press Start, and the timer counts down to zero and alerts you.
Set a Countdown and Run Up to Five Named Timers
Countdown Timer Formula
Where:
- \(H\), \(M\), \(S\) — the hours, minutes and seconds you enter (each from 0 to 999)
- \(T_{\text{total}}\) — total duration of the timer in seconds
- \(T_{\text{elapsed}}\) — seconds passed since you pressed Start
- \(T_{\text{left}}\) — remaining time, rounded up to the next whole second
The first line converts the three fields into one duration in seconds; the second line is what the large display shows — the duration shrinking as time passes. When \(T_{\text{left}}\) reaches zero, the timer ends, the display flashes and the alarm sounds.
Countdown Timer – Calculation Example
Example: you enter the default settings — Timer Name “Timer 1”, Hours 0, Minutes 10, Seconds 0 — and press Start.
\[ T_{\text{total}} = 3600 \times 0 + 60 \times 10 + 0 = 600 \text{ s} = 10{:}00 \]
Four minutes after starting, \(T_{\text{elapsed}} = 240\) seconds:
\[ T_{\text{left}} = 600 - 240 = 360 \text{ s} = 06{:}00 \]
Result: the display reads 06:00, and the alarm fires when the count reaches 00:00 — exactly 10 minutes after you pressed Start.
How to use the calculator
- Type a Timer Name such as “Laundry”, “Oven” or “Workout” — it appears next to each countdown in the timer list.
- Set the duration with the Hours, Minutes and Seconds fields. Each accepts whole numbers from 0 to 999, and the duration must be at least one second.
- Adjust the alarm: pick an Alarm Tone (Classic beeps, Soft chime or Buzzer), set the Volume (%), and tick Repeat alarm until stopped if you want it to keep sounding, or Browser notification when a timer ends for a pop-up alert (your browser asks for permission the first time).
- Press Start — or the Space key — to run the timer. The big display counts down, Start turns into Pause, and pressing Space again pauses or resumes.
- Use the quick-start presets (1, 3, 5, 10, 15, 30, 60 min) to create and immediately run a timer with one click.
- Press Add timer to queue more timers from the same fields, up to five at once. Click a row in the timer list to select it; Start/Pause, Reset and +1 min always act on the selected timer. Each row also has its own play/pause, +1:00, reset and delete (✕) buttons.
- Use Full screen to enlarge the countdown — handy across the room or for presentations.
What a countdown timer is and how it works
A countdown timer measures a fixed interval backwards: you give it a duration, it subtracts the time that passes, and it signals when nothing is left. Unlike a clock, which tells you the time of day, a countdown answers a different question: “how long until X happens?” That makes it the standard tool for cooking, workouts, study sessions, laundry, parking meters, presentations, games and any task with a deadline attached.
This timer runs entirely in your browser and derives the remaining time from the wall clock rather than by accumulating ticks. That detail matters in practice: even if the tab is throttled in the background, the countdown on screen when you return is exact, not several seconds behind. The remaining time also appears in the browser tab title, so a glance at your tabs is enough to check on progress.
Running timers are saved in your browser’s local storage and keep counting across a page reload. If a timer finishes while the page is closed or your device was asleep, the display and alarm will notify you as soon as you return. Because the state lives in your browser, timers are not shared between devices or browsers — reopen the same page in the same browser to pick up where you left off.
Reading the result is simple: the large display shows the selected timer’s remaining time as MM:SS or H:MM:SS when hours are involved. When the count hits zero the display and the matching row flash, and the alarm plays once or repeats until you press a timer button, depending on the repeat setting.
Assumptions, limits and practical tips
- Maximum of five timers. You can keep five timers at once; delete one before adding another.
- The page must stay open for sound. The alarm is generated by the browser playing the page, so close the tab only if you will return before the deadline — the timer will still be correct, but it cannot beep while closed. On mobile, keeping the screen on or staying on the page avoids OS suspensions that silence audio.
- Notifications are optional. The browser-notification option works only while the page is open and you granted permission; the sound alarm alone is enough in most cases.
- Names are trimmed to 40 characters and fields to whole numbers 0–999; durations can range from 1 second up to about 41 days.
- +1 min is a safety valve. If something needs “just a bit longer”, add a minute on the fly instead of rebuilding the timer — Reset then restores the original full duration.
- For measuring how long something already took instead of counting down, use the online stopwatch with laps; to find the length of an interval between two clock times, the time duration calculator or the time calculator for adding and subtracting time will do it in one step.
Quick duration reference
| Common task | Suggested timer |
|---|---|
| Plank / short exercise round | 1 min |
| Tea brewing | 3 min |
| Pomodoro-style focus sprint | 25 min (set 5 min for the break) |
| Boiling an egg, runny yolk | 5–6 min |
| Laundry wash cycle reminder | 30–60 min |
| Oven dish check | 10–15 min |
Any of these can be started with a single quick-start preset button or typed into the Hours / Minutes / Seconds fields.
Frequently Asked Questions
Can I set a countdown for days, or a duration longer than 24 hours?
Yes. The Hours field accepts values up to 999, so the longest possible timer is 999 hours 999 minutes 999 seconds — just over 41 days. For a 3-day timer, enter Hours 72. The display switches from MM:SS to H:MM:SS as soon as hours are involved, and the browser tab title keeps showing the remaining time even then.
Why doesn't the alarm ring if I close the tab or my phone goes to sleep?
Browsers only let an open page play sound, so the alarm cannot beep while the tab is fully closed or the OS suspends the page. The countdown itself stays accurate, because remaining time is computed from the wall clock — and any timer that finished while you were away will flash and sound as soon as you return. For critical reminders, keep the page open and, on phones, keep the screen on.
Do my running timers survive a page refresh?
Yes. Running timers and their remaining time are stored in your browser's local storage and reloaded, still counting, when you reopen the same page in the same browser. Note they are not synced between devices or different browsers — reopening the page on another phone or in another browser starts with a clean slate.
How do I convert minutes and seconds into one duration by hand?
Use \( T = 3600H + 60M + S \) to get the total in seconds. For example, 1 hour 45 minutes 30 seconds is \( 3600 + 45 \times 60 + 30 = 6330 \) seconds. This is exactly what the calculator does internally — handy if you ever need to check a timer against a recipe in seconds or convert a duration between units yourself.
How many timers can run at the same time?
Up to five. Enter a name and duration, press Add timer, then repeat — each row gets its own start/pause, +1:00, reset and delete buttons, and all five can count down simultaneously. This is useful when the oven, the laundry and the kettle all run at once. To add a sixth, delete one first.
I don't hear anything when the timer ends — what's wrong?
Check three things: the Volume field must be above 0%, your device or browser tab must not be muted, and the page must be open. Also, browsers only allow audio after you have interacted with the page, which pressing Start normally covers. If your device was asleep, the alarm plays when you come back rather than at the original end time.
What's the difference between a countdown timer and a stopwatch?
A countdown starts at a duration you choose and runs backwards to zero, telling you how long until something finishes. A stopwatch starts at zero and counts up, measuring how long something already took. Use this timer for cooking, parking, workouts or deadlines; use a stopwatch when you want to record elapsed time, for example laps while running or the length of a meeting.