Interval timer for HIIT, Tabata and circuits
A work/rest interval timer for HIIT, Tabata and circuit training. Set your phases once and follow the audio cues, so you can focus on the exercise instead of watching a clock or counting reps in your head.
How it works
You define four values: prepare (a get-ready countdown), work (the active interval), rest (recovery between intervals) and the number of rounds. When you press Start, the timer counts down the prepare phase, then alternates work → rest for each round, showing the current phase and round number. At every phase change it plays a beep generated with the Web Audio API, so the cue works offline with no audio file to download. Setting rest to 0 chains work intervals back to back.
Popular protocols and how to set them up
Classic Tabata (4 minutes)
| Phase | Duration | Rounds |
|---|---|---|
| Prepare | 10 s | 1 |
| Work | 20 s | 8 |
| Rest | 10 s | between each work |
Total: 10 s prepare + 8 × 30 s = 250 s. Tabata calls for maximal effort during work intervals; the 10-second rest is intentionally too short to recover.
Standard HIIT (20 minutes)
| Phase | Duration | Rounds |
|---|---|---|
| Prepare | 15 s | 1 |
| Work | 40 s | 20 |
| Rest | 20 s | between each work |
A 40:20 ratio is harder than Tabata’s 20:10 in absolute terms but easier to sustain at submaximal effort for a longer session.
Active-rest circuit (strength bias)
| Phase | Duration | Rounds |
|---|---|---|
| Prepare | 10 s | 1 |
| Work | 45 s | 12 |
| Rest | 60 s | between each work |
Longer rest allows more recovery for compound lifts. Set rest to 60–90 s for exercises like squats or kettlebell swings where quality matters more than density.
Continuous circuit (no rest between stations)
Set rest to 0. The timer chains work intervals back to back, useful for timed circuits where the transition between exercises serves as informal recovery.
Practical tips
Use the prepare phase every time. Even 5–10 seconds lets you set up your position, grip, or starting stance before the first work interval begins. Starting cold from zero often means the first round is wasted getting into position.
Keep the screen visible but not necessary. The audio cues are the primary signal — one beep for work, a different pattern for rest, a final cue when the session ends. Once you know the cues, you can look away from the screen entirely and focus on form.
Work-to-rest ratio determines intensity. A 1:2 ratio (20 s work, 40 s rest) is recovery-heavy and suits high-power output like sprints. A 2:1 ratio (40 s work, 20 s rest) is metabolically demanding and suits aerobic intervals. Equal work and rest (1:1) sits in between and is a common starting point.
Keep the device awake. Browsers may pause timers and audio when a tab goes to background or the screen locks. Keep the tab in the foreground and prevent auto-lock while the timer is running.
Everything runs in your browser — the audio cues are generated locally, so the timer works offline and nothing about your workout is ever uploaded.