HIIT Workout Timer

Intervals{{ resultsReady ? computation.values.work_interval_count : '—' }} Work density{{ resultsReady ? formatPercent(computation.values.interval_work_density_percent) : '—' }} Plan{{ profileLabel }}

{{ livePhaseLabel }}{{ liveExerciseLabel }}

Workout template:

Choose a starting shape, then adjust the rotation and timing below.

Exercise rotation:

Use 1–24 nonblank lines in the form Exercise | optional cue.

Work interval:

5–300 seconds. Keep repeatability and movement quality ahead of density.

Rest interval:

0–300 seconds between consecutive work intervals.

Rounds:

1–20 complete rotations; the plan is also capped at 240 work intervals.

rounds

Warm-up:

0–900 seconds before hard work begins.

Recovery between rounds:

0–600 seconds after each full rotation except the last.

Cooldown:

0–900 seconds after the interval block.

Start countdown:

0–120 seconds before warm-up or the first work interval.

Cue style:

Cue wording never changes the canonical timing model.

Sound cues:

Audio starts only from a user action and remains browser local.

Sound volume:

{{ sound_volume }}%; inactive while sound cues are off.

Vibration cues:

Unsupported devices ignore vibration without changing the timer.

Keep screen awake:

The wake lock is released on pause, reset, completion, or navigation.

Workout brief

{{ row.label }}{{ row.display }}

Timing method:

total = prep + warm-up + work + interval recovery + cooldown

interval density = work / (work + interval recovery) × 100

The chart renderer is unavailable. Planned phase seconds remain available in the workout brief and interval schedule.

Elapsed	Event	Phase	Detail	Copy
{{ formatDuration(row.elapsed_seconds) }}	{{ row.event }}	{{ row.phase }}	{{ row.detail }}

High-intensity interval training alternates demanding efforts with easier recovery. There is no single universal work length, rest length, or number of cycles that defines every HIIT session. The useful pattern is repeatable effort: work hard enough to create the intended challenge, recover enough to begin the next interval with control, and stop before fatigue makes the movement unsafe.

Timing changes the character of a workout even when the exercise list stays the same. Forty seconds of work followed by twenty seconds of rest devotes two-thirds of that repeating interval block to work. Thirty seconds followed by thirty seconds divides it evenly. Neither ratio states the actual intensity, because pace, resistance, movement complexity, fitness, and range of motion still determine the physical demand.

Work interval sets the duration of each hard effort, not a guaranteed effort level.
Short rest separates exercises within a round and helps prepare for the next movement.
Round recovery replaces the short rest after the last exercise of each non-final round.
Warm-up and cooldown sit outside the interval density calculation but remain part of complete session time.

Exercise rotation matters because transitions consume attention even when they are not separately timed. Simple names and compatible positions reduce confusion. A rotation that repeatedly switches between the floor, standing work, and equipment can need longer recovery than a bodyweight sequence with the same arithmetic.

The talk test offers one practical clue for aerobic intensity. During vigorous activity, speaking more than a few words normally requires pausing for breath. That clue is relative to the person, not a reason to chase breathlessness. Someone returning after inactivity may experience a modest exercise as vigorous, while a trained person may need more speed or resistance for the same response.

Intervals are general fitness practice, not a medical test or treatment. Build volume gradually, keep movement quality ahead of pace, and stop for chest pain, faintness, dizziness, unusual shortness of breath, or sharp pain. People with health concerns or a long break from exercise should obtain appropriate professional guidance before demanding intervals.

How to Use This Tool:

Choose a workout shape that you can repeat cleanly, then check the complete phase order before starting.

Select a Workout template or enter one exercise per line in Exercise rotation. Add an optional cue after a pipe when a movement needs a short reminder.
Set Work interval, Rest interval, and Rounds. Use Recovery between rounds for the longer pause after a full rotation rather than inflating every short rest.
Choose warm-up, cooldown, and start-countdown durations. These phases change complete session time and session density, but not interval density.
Review the Workout brief and effort mix. Reduce exercises or rounds if the plan exceeds 240 work intervals, and shorten the plan if it exceeds two hours.
Choose visible, sound, or vibration cues only after testing device support. Press Start to freeze the current sequence for the run; changes made during the session apply at the next start.

Interpreting Results:

Interval work density compares work with short rest and round recovery. Session work density uses the entire session, including preparation, warm-up, and cooldown. The session value will be lower whenever any of those setup phases has a positive duration.

Use density to compare timing plans only after checking that the exercise rotation, pace, resistance, and participant are comparable. A higher percentage is not automatically a better workout, and two sessions with the same percentage can produce very different physical demands.

The run log records timer events rather than repetitions, heart rate, technique, or completed work. A completed clock confirms that the schedule elapsed; it cannot confirm that every interval was performed as written.

Technical Details:

The phase sequence begins with optional preparation and warm-up. Each exercise receives one work phase per round. A short rest follows every work phase except the last exercise of a round; after that exercise, non-final rounds use the separate round recovery, while the final work phase leads directly to the cooldown.

Transformation Core

Ordered HIIT phase construction rules
Position	Phase added	Omission rule
Before intervals	Preparation, then warm-up	Either disappears when its duration is 0.
Within a round	Work, then short rest	Zero-second rest disappears.
End of a non-final round	Work, then round recovery	Round recovery replaces short rest and disappears at 0 seconds.
End of final round	Final work phase	No short rest or round recovery follows it.
After intervals	Cooldown	It disappears when its duration is 0.

Formula Core

Let e be the number of exercises, R the rounds, w work seconds, r short-rest seconds, and b round-recovery seconds.

\begin{matrix} W & = & e R w \\ Q & = & R (e - 1) r + (R - 1) b \end{matrix}

Setup time A is preparation plus warm-up plus cooldown. Total time and the two density measures follow from those three components.

\begin{matrix} T & = & W + Q + A \\ D_{interval} & = & \frac{W}{W + Q} \times 100 \\ D_{session} & = & \frac{W}{T} \times 100 \end{matrix}

Work and short rest accept 5 to 300 and 0 to 300 whole seconds respectively. Rounds accept 1 to 20, warm-up and cooldown 0 to 900 seconds, round recovery 0 to 600 seconds, and preparation 0 to 120 seconds. The rotation accepts 1 to 24 nonblank lines, while exercise count multiplied by rounds must not exceed 240.

Percentages retain full numeric precision and are rounded only for display. Cue wording, sound, vibration, and screen-wake choices do not alter the phase arithmetic.

Safety Notes:

Warm-up and cooldown can ease the change in heart rate and breathing at the beginning and end of activity, but their presence does not make an unsuitable interval safe. Select movements that remain controllable under fatigue and leave room for equipment changes.

Start with light or moderate activity and increase volume or intensity gradually when fitness is low or the routine is unfamiliar.
Skip or replace an exercise that causes pain, loss of balance, or repeated technique breakdown.
Do not rely on audio, vibration, or screen-wake features without a visible fallback.

Worked Examples:

Five-exercise bodyweight rotation

Five exercises repeated for three rounds at 40 seconds work and 20 seconds rest create 600 work seconds. Twelve short rests contribute 240 seconds and two 60-second round recoveries add 120 seconds. With 10 seconds of preparation, a 180-second warm-up, and a 120-second cooldown, the complete session is 1,270 seconds, or 21 minutes 10 seconds. Interval density is 62.5%; complete-session density is about 47.2%.

References:

Physical Activity Guidelines for Americans, 2nd edition, U.S. Department of Health and Human Services, 2018.
Measuring Physical Activity Intensity, Centers for Disease Control and Prevention.