About the HIIT Interval Timer
This HIIT interval timer runs any work/rest workout in your browser. Set the length of each work interval and rest interval, how many rounds make a set, how many sets you want and how long to recover between sets. Press start and the timer counts every phase down in large digits, beeps at each change and gives a 3-2-1 countdown before work begins — no app or sign-up needed.
Use it for high-intensity interval training, circuit and bodyweight sessions, kettlebell and boxing drills, running or cycling intervals on a treadmill or trainer, and stretching or mobility holds. The planner below the timer shows the total session length, how much of it is work, and a full schedule, so you can design a workout that fits the time you have before you begin.
Timing is based on the system clock rather than counting ticks, so it stays accurate even if your phone screen dims or the tab is in the background. Keep the tab open and the sound on to hear the cues. Each round is counted as one work interval followed by one rest interval; set rest is added between sets.
With the default inputs, the total workout time is 26m 10s. Change any value above to recalculate instantly.
How to use the hiit interval timer
- 1Set the work and rest interval lengths in seconds.
- 2Choose how many rounds make up a set and how many sets to do.
- 3Add rest between sets and an optional get-ready and cool-down period.
- 4Press Start — listen for the 3-2-1 beeps and the tone at every change.
- 5Pause or skip a phase at any time; Reset starts the workout over.
Formula and method
Every round is one work interval followed by one rest interval, so a set lasts rounds × (work + rest). Sets are separated by the longer set rest, which is not added after the final set. The get-ready countdown and the optional cool-down are added at the start and end.
The work share is total work time divided by total session time, and the work-to-rest ratio is reduced to its simplest form (40 s on and 20 s off is 2 : 1). The live timer follows exactly the same sequence, using the system clock so each phase ends on time even if the browser throttles a background tab.
- work, rest
- Length of each work and rest interval (seconds)
- rounds
- Work/rest pairs per set
- sets
- Number of sets
- set rest
- Recovery between sets (seconds)
Worked examples
40/20 HIIT, 8 rounds × 3 sets
Each set is 8 × (40 + 20) = 480 s. Three sets make 1,440 s, plus two 60 s set rests and the 10 s get-ready gives 1,570 s (26:10). Work totals 24 × 40 = 960 s, about 61% of the session.
Classic Tabata
Eight rounds of 20 s work and 10 s rest last 8 × 30 = 240 s (4 minutes). With a 10 s get-ready the timer runs for 250 s, of which 160 s is all-out work.
Running intervals: 6 × 3 min with 90 s jog, 5 min cool-down
Six rounds of 180 s hard plus 90 s easy take 6 × 270 = 1,620 s; adding a 300 s cool-down makes 1,920 s (32 minutes). The hard running totals 18 minutes, 56.25% of the session.
Frequently asked questions
What is a good HIIT interval?+
Common formats are 20 s on / 10 s off (Tabata), 30/30, 40/20 and 45/15 for circuits, and 1–4 minute repeats with equal or shorter recovery for running and cycling. Shorter rest makes the session harder and more aerobic.
How long should a HIIT workout be?+
Most HIIT sessions include 10–30 minutes of intervals plus a warm-up and cool-down. Because the work is intense, quality drops off quickly; it is better to do fewer high-quality rounds than many sloppy ones.
Will the timer keep running if my screen locks?+
The countdown is calculated from the system clock, so the time stays correct when you return. Some phones pause audio and timers in a locked or background tab, so keep the screen on during the workout for reliable beeps.
What is the difference between rounds and sets?+
A round is one work interval plus its rest. A set is a group of rounds, for example 8 rounds of one exercise. Sets are separated by a longer recovery so you can change exercise or catch your breath.
Can I use it for Tabata or EMOM?+
Yes. For Tabata set 20 s work, 10 s rest and 8 rounds — or use the dedicated Tabata timer. For an EMOM-style workout set work to the minute length and rest to 0, and finish your reps inside each minute.