HIIT Interval Timer Calculator
Calculate total HIIT workout time from work duration, rest duration, and number of rounds.
Returns total time, work-to-rest ratio, and calorie burn.
Interval training alternates periods of high-intensity effort with rest or low-intensity recovery. It is one of the most efficient methods for improving cardiovascular fitness, speed, and calorie burn in less time than steady-state cardio.
Core formula: Total Session Time = (Work + Rest) × Rounds × Sets + (Set Rest × (Sets − 1))
Where:
- Work = duration of each high-intensity effort (seconds)
- Rest = recovery time between efforts (seconds)
- Rounds = number of work-rest cycles per set
- Sets = number of sets in the session
- Set Rest = longer recovery between sets (seconds)
Common interval protocols:
| Protocol | Work | Rest | Ratio | Use Case |
|---|---|---|---|---|
| Tabata | 20 s | 10 s | 2:1 | Peak anaerobic power |
| HIIT standard | 30 s | 30 s | 1:1 | General fitness |
| Sprint interval | 10 s | 50 s | 1:5 | Max speed development |
| Aerobic interval | 3 min | 3 min | 1:1 | VO₂ max improvement |
Work-to-rest ratio matters most:
- 1:1 ratio → taxes both aerobic and anaerobic systems equally
- 1:2 or 1:3 ratio → allows fuller recovery, supports higher peak output
- 2:1 ratio (Tabata) → accumulates maximal metabolic stress in 4 minutes
Worked example: A cyclist performs 8 rounds of 40-second sprints with 20 seconds rest, for 3 sets with 2 minutes between sets.
Total = (40 + 20) × 8 × 3 + (120 × 2) = 1,440 + 240 = 1,680 seconds (28 minutes)
Heart rate targets: Work phase should reach 80–95% of max HR. Rest phase should allow recovery to 60–70% before the next interval begins. Monitoring this ratio ensures productive training without overtraining.