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Interval Timer
Use this free interval timer online for HIIT and circuit workouts. Set your work and rest seconds, rounds, sets, warm-up, and cool-down, then press Start: the timer counts down each phase, beeps when it changes, and shows your round, set, and time left until the session is done.
Ready
00:30
Round — of 8 · Set — of 1
Session total: 7 min 10 sec
| Part | Time |
|---|---|
| Warm-up | 1 min 0 sec |
| Work time | 4 min 0 sec |
| Rest time | 1 min 10 sec |
| Cool-down | 1 min 0 sec |
| Session total | 7 min 10 sec |
Keep this page open and your sound on while the timer runs. The beeps are made in your browser, so no audio file is downloaded.
How it works
Interval training means alternating short bursts of hard effort with short rests, then repeating. Instead of jogging steadily for 30 minutes, you might sprint for 30 seconds, walk for 10 seconds, and repeat that eight times. The timer keeps track of the switching so you can focus on the exercise instead of watching a clock.
Work is the number of seconds you exercise hard in each round, and rest is the number of seconds you recover before the next round. Rounds are how many work blocks make up one set, and sets are how many times the whole round block repeats. A short break of one or two minutes between sets is common in real training, but this timer keeps the structure simple: sets run back to back, so add a longer rest into your rest value if you want a break between sets, or pause the timer between sets.
Rest time = rest seconds × (rounds × sets − 1)
Session total = warm-up + work time + rest time + cool-down
Notice that rest is counted one fewer time than work. There is no rest after the very last work block, because the session moves straight into the cool-down. With 8 rounds and 1 set, there are 7 rests, not 8. That is the detail most people get wrong when they add the numbers up by hand, and it is why the worked example below counts 7 rests for 8 rounds.
The timer itself runs on your device clock. When you press Start, it builds the full list of phases — warm-up, then work and rest blocks, then cool-down — and counts each one down second by second. It beeps once when a phase changes, twice when a set ends, and three times when the session finishes. Pause freezes the countdown where it is, and Reset returns to the first phase with your current settings. Changing any setting while the timer is stopped rebuilds the session and updates the total.
The sound is made with Web Audio, the sound feature built into modern browsers, so there is no audio file to download and nothing to install. Your browser only allows sound after you interact with the page, which is why the first beep happens after you press Start. If you hear nothing, check that your device volume is up and the tab is not muted.
Worked example
You plan a session with 30 seconds of work, 10 seconds of rest, 8 rounds, 1 set, a 60-second warm-up, and a 60-second cool-down.
Step 1: Work time — 30 × 8 × 1 = 240 seconds, or 4 minutes.
Step 2: Rest time — there are 8 × 1 − 1 = 7 rests, so 10 × 7 = 70 seconds, or 1 minute 10 seconds.
Step 3: Add warm-up and cool-down — 60 + 60 = 120 seconds.
Step 4: Session total — 60 + 240 + 70 + 60 = 430 seconds, which is 7 minutes 10 seconds.
The result is 7 min 10 sec total (430 seconds) — exactly what the calculator shows for those inputs.
FAQ
What is a good work-to-rest ratio for HIIT?
A common starting point is 30 seconds of work and 30 seconds of rest, a 1-to-1 ratio, or 30 seconds of work and 15 seconds of rest, a 2-to-1 ratio, for 6 to 10 rounds. Beginners do better with longer rests, such as 20 seconds of work and 40 seconds of rest. As your fitness improves, shorten the rest rather than lengthening the work. Pick a ratio you can hold with good form through the last round.
How many rounds should an interval workout have?
Most interval workouts use 6 to 12 rounds per set, with 1 to 3 sets in total. Eight rounds of 30 seconds of work is 4 minutes of hard effort, which is plenty for a first session. If you finish the last round feeling fresh, add rounds or shorten the rest next time. If your form falls apart halfway, cut the rounds or lengthen the rest.
Does this interval timer make a sound?
Yes. The timer plays a short beep through your device speakers when each phase changes, a double beep when a set ends, and a triple beep when the whole session finishes. The sound is made in your browser with Web Audio, so there is no audio file to download. Make sure your sound is on and your browser tab is not muted, and keep the page open while the timer runs.
Should I include a warm-up and cool-down?
Yes. A warm-up of 3 to 5 minutes of light movement, such as marching in place, arm circles, and easy squats, raises your heart rate gradually and lowers the chance of a pulled muscle. A cool-down of 2 to 3 minutes of slow walking and gentle stretching helps your heart rate come back down. This timer has separate warm-up and cool-down fields so both are part of the session total.
Can I use this timer for Tabata?
Yes. Tabata is 20 seconds of work and 10 seconds of rest for 8 rounds, which is one set of 4 minutes. Set work to 20, rest to 10, rounds to 8, and sets to 1. Traditional Tabata uses a single exercise at maximum effort, so only choose it if you are already comfortable with high-intensity training, and keep the warm-up on.