Interval Timer (HIIT)
Enter work, rest, rounds and sets or tap a preset – the timer guides you through the workout with colours and beeps. Your settings are part of the link, so you can bookmark or share your programme.
How it is calculated
How the interval timer works
Interval training alternates work and rest at fixed times. Set work and rest in seconds, the number of rounds per set, the number of sets and the longer set break in between. After the last round of a set there is no round rest – the set break or the end follows directly. A rest of 0 seconds gives intervals without a break, e.g. “a new exercise every minute”.
Worked example: 40 s work, 20 s rest, 8 rounds, 3 sets, 60 s set break: each set is 8 × 40 + 7 × 20 = 460 s, plus 2 set breaks = 3 × 460 + 120 = 1500 s, i.e. 25 minutes, 16 of them work. The totals appear under the progress bar before you start.
Presets
- 20/10 × 8 – the Tabata scheme from the study by Tabata et al. (1996), just under 4 minutes.
- 30/30 × 10 – equal work and rest, a good start.
- 40/20 × 8 and 45/15 × 6 – common HIIT and circuit formats.
- 60/0 × 10 – a new round starts every full minute (EMOM style).
A preset fills in the fields and the address changes with it – save your own programmes as bookmarks or send them to your training group with “Share”.
Context
The WHO recommends at least 150 minutes of moderate activity per week for adults; high-intensity intervals are one way to cover part of it in less time. How hard a session is depends on the intensity in the work phases, not on the timer. The timer measures neither heart rate nor power. If you have a health condition or have not trained for a long time, check with a doctor before high-intensity training.
Signals and display
Work is red, rest green, the get-ready phase yellow. Three short beeps sound in the last three seconds of each phase, a high tone marks work, a low tone rest, and a final signal the end. “Skip” jumps to the next phase; fullscreen enlarges the display for training at a distance.
Technical details
Phase and remaining time are calculated from the elapsed time on every frame, so the sequence stays correct after a tab switch. The beeps are scheduled at the start on the browser’s audio clock (Web Audio API) and play on time in a background tab too. Where available, the screen stays on while the timer runs (Screen Wake Lock API). Nothing is uploaded.
Frequently asked questions
What is an interval timer?
A timer that switches automatically between work and rest and counts the rounds – for HIIT, circuit training, running intervals or skipping. You do not have to watch the clock yourself.
Which intervals are good for beginners?
A common starting point is equal work and rest, such as 30/30 seconds for 6 to 10 rounds, moving to shorter rests like 40/20 later. What matters is that your form stays clean until the last round.
Does the interval timer work on iPhone and Apple Watch?
It runs in every current browser, including Safari on iPhone. Nothing is sent to an Apple Watch. For the beeps the silent switch must be off; the browser enables sound after you tap Start.
Can I use it for running intervals?
Yes, for example 60 s fast / 90 s easy × 8 rounds. For longer intervals just enter the seconds, e.g. 180 for three minutes. Where supported, the screen stays on while it runs.
Can I save my own workouts?
All values are stored as parameters in the page address. Bookmark the page or tap “Share” – opening the link sets up the workout immediately. Your browser also remembers your last entries locally.
Is there an interval timer with sound?
Yes: beeps in the last three seconds of each phase, a high tone for work, a low tone for rest and a final signal. You can switch them off with the checkbox. The timer does not play music, but works alongside a music app.
Sources and legal basis
- Tabata I., Nishimura K., Kouzaki M. et al. (1996): Effects of moderate-intensity endurance and high-intensity intermittent training on anaerobic capacity and VO2max. Med Sci Sports Exerc 28(10), 1327–1330
- WHO: Physical activity – Fact sheet
- MDN Web Docs: Web Audio API
- MDN Web Docs: Screen Wake Lock API
As of:
Related tools
- Tabata TimerFree Tabata timer: 20 s work, 10 s rest, 8 rounds, countdown beeps and get-ready time. Multiple sets, fullscreen, runs in your browser with no app needed.
- Online TimerFree online countdown timer: enter any time or tap a 5, 10 or 15 minute preset, get an alarm when time is up, remaining time in the tab. No sign-up.
- Online StopwatchFree online stopwatch with lap times, fastest/slowest lap and copy-to-clipboard. Keeps running after switching tabs or reloading the page.
- Heart Rate Zone CalculatorCalculate your training heart rate zones: enter your max heart rate or estimate it with Tanaka, then get zones as % of max HR or with the Karvonen method.
- Binaural beats generatorBinaural beats online: set carrier and difference frequency, a separate sine tone for each ear, with timer and headphone test. No health claims.
- BMI calculator (WHO categories)Calculate your body mass index in lb and ft/in or kg and cm. See your WHO category, from underweight to obesity class III, and the healthy weight range.