Interval Timer
8 rounds of 20 seconds of work and 10 seconds of rest take 3:50 here, because there is no rest after the last round. Every length is adjustable (default work 30 s, rest 15 s).
How to use
- Enter the work time and rest time in seconds, the number of rounds, and a get-ready time. Set rest to 0 for back-to-back rounds, or get-ready to 0 to start straight away.
- The total time appears under the fields, so you can check the session length before you start.
- Press Start. You hear beeps for the last three seconds of every phase, a higher tone when work starts and a lower tone when rest starts, and a finishing chime at the end.
- Skip moves to the next phase, Pause stops the clock, and Reset returns to the start and unlocks the fields.
How it works
The session is a list of phases: get ready, then work and rest for each round. There is no rest after the final round. The total time is get ready + rounds x work + (rounds - 1) x rest.
The timer reads the browser's high-resolution clock, performance.now(), and works out which phase the elapsed time falls in. It does not count screen updates, so it stays correct when the tab is in the background.
For example, 20 seconds of work and 10 seconds of rest for 8 rounds with no get-ready time totals 8 x 20 + 7 x 10 = 230 seconds, which is 3:50.
Example setups
| Use | Work | Rest | Rounds |
|---|---|---|---|
| Tabata style | 20 s | 10 s | 8 |
| Beginner HIIT | 30 s | 30 s | 8 |
| Circuit station | 45 s | 15 s | 6 |
| Stretching holds | 30 s | 5 s | 10 |
| Study sprint | 120 s | 30 s | 5 |
Choosing the numbers
These are starting points, not prescriptions. Pick work and rest times you can repeat with good form for every round, and adjust after your first session. If you have a health condition or are new to hard exercise, check with a qualified professional before you try intense intervals.
FAQ
Does it include rest after the last round?
No. The session ends when the last work phase ends. If you want a final rest included, add one to the total yourself or treat the last rest as your cool-down.
Can I use it for the Tabata pattern?
Yes. Tabata is usually described as 20 seconds of work and 10 seconds of rest for 8 rounds. Enter those numbers and set get-ready to 0 or 10 seconds. Because this timer skips the last rest, a full session lasts 3:50 and not 4:00.
Will the beeps play in a background tab?
The timer keeps its schedule from the clock, so phases switch at the right time. Browsers can limit audio in tabs you are not looking at, so press Start on this page and keep the sound on. The tab title shows the time left either way.
What are the limits?
Work can be 1 to 3600 seconds, rest 0 to 3600, get-ready 0 to 600, and rounds 1 to 99.
Is anything saved or uploaded?
No. Everything stays in your browser, and reloading the page resets the timer.