How to use the interval timer
- Presets: optional. Press a preset such as Tabata or Boxing to fill in Work, Rest and Rounds.
- Prep (seconds): a get-ready countdown before round 1. Use 0 to start straight away.
- Work (seconds) and Rest (seconds): how long each effort and each break lasts.
- Rounds: how many work periods to do. The line under the fields shows the total time.
- Press Start. Use Pause and Resume to stop the clock, Reset to start over, and Beeps to turn the sound off.
How the timer works
The workout is a list of periods: prep, then work, then rest, repeated for each round. Total time is prep + rounds × work + (rounds - 1) × rest, because there is no rest after the last round. The clock measures real elapsed time, so a delayed timer does not make it drift. Cues are a high tone when work starts, a low tone when rest starts, short ticks for the last three seconds of a period, and three beeps at the end. The 20 seconds on, 10 seconds off pattern comes from Tabata and colleagues (1996). Where the browser supports the Screen Wake Lock API, the screen stays on while the timer runs.
Worked example
With the defaults (Prep 5, Work 30, Rest 10, Rounds 8) the summary reads Total time 05:15: 5 s prep, then 8 rounds of 30 s work with 10 s rest between rounds. The display starts at 00:05 on "Get ready". At 0:05 the high tone sounds and round 1 of 8 begins. Work ends at 0:35, rest runs to 0:45, and round 2 starts. Round 8 begins at 4:45 and ends at 5:15, when the screen shows "Done!".
Limits and edge cases
- Settings must be whole numbers: Prep 0 to 600, Work 1 to 3,600, Rest 0 to 3,600, Rounds 1 to 500. Anything else shows a message in red.
- Rest 0 runs the work periods back to back.
- The fields lock while a workout runs. Press Reset to change them. Your last settings are remembered in your browser.
- Keep the tab open. Phone browsers may pause audio when you lock the screen or switch apps.
- For the classic 20/10 protocol with a fixed layout, use the Tabata timer. For 25 minute focus blocks use the Pomodoro timer, and for one-off durations use the countdown timer.
Frequently asked questions
What work and rest times should I use for HIIT?
Common choices are 30 seconds of work with 10 seconds of rest, 40/20 and 45/15. The original Tabata study used 20 seconds of very hard cycling and 10 seconds of rest, 7 to 8 times. Pick times you can repeat with good form, and ask a doctor first if you have a health condition.
How long is a Tabata workout on this timer?
The Tabata preset (20 s work, 10 s rest, 8 rounds) runs 3 minutes 50 seconds, because there is no rest after the last round. With the default 5 second prep the summary shows 03:55.
What do the beeps mean?
A high tone starts a work period, a low tone starts a rest period, short ticks count down the last three seconds of a period, and three beeps mean the workout is finished. Press Beeps to turn the sound off.
Can I use it for boxing rounds, circuits or studying?
Yes. The Boxing preset gives three 3 minute rounds with 1 minute of rest, and a circuit can be 45 seconds at each station with 15 seconds to move.
Will it keep running if I switch tabs or lock my phone?
On a computer it keeps counting in a background tab because it measures elapsed time, though a throttled tab may play a cue a little late. On a phone the screen stays awake while the timer runs where the browser allows it, but locking the screen or switching apps may pause the sound, so keep the page in view.
Sources: Tabata I, et al. (1996), Medicine and Science in Sports and Exercise 28(10):1327-1330; MDN, Screen Wake Lock API.