HIIT timer 40/20 vs 45/15 vs 30/30: pick one
No single ratio is proven best. If you are new to HIIT, start at 30 seconds of work and 30 of rest; move to 40/20 when you can keep your effort level steady through every round; 45/15 is for people who recover quickly and already train hard. Choose the ratio the exercise allows, not the number you saw on a video.
The test is whether you can do your last work interval at nearly the same effort as your first. If you fade badly by round four, the ratio is too hard, or the exercise is. If you finish feeling you had plenty left, shorten the rest or lengthen the work.
In the Tabata ratio, 20/10, the work is short and sharp, so it only makes sense when the effort inside the 20 seconds is truly hard. 30/30 is equal work and rest, 40/20 is two thirds work and 45/15 is three quarters work. The numbers are just seconds on and seconds off, and the ratio is the share of time spent working.
What the numbers mean
A work/rest ratio writes two things together: how many seconds you work and how many you rest. In 40/20, you work 40 seconds, rest 20, then go again. The cycle is 60 seconds, so it fits a clock neatly. 30/30 and 45/15 are also 60-second cycles, and 20/10 is 30 seconds. That is a reason these four are popular: they are easy to count and easy to program.
| Ratio | Cycle | Share working | Typical use |
|---|---|---|---|
| 20/10 | 30 s | 67% | Short blocks of very hard work, such as the Tabata protocol |
| 30/30 | 60 s | 50% | Beginners, running intervals, hard moves |
| 40/20 | 60 s | 67% | General circuit and HIIT classes |
| 45/15 | 60 s | 75% | Fit exercisers, simple moves |
The effect on a session: with the same number of rounds, 45/15 puts you under load for 50% more time than 30/30, in the same total time.
What the research does and does not say
Be careful with claims here. The research behind these numbers is narrow, and most of what is quoted online goes beyond it.
The Tabata study (20/10). The paper is Tabata et al., Medicine and Science in Sports and Exercise, 1996. According to its abstract, one group trained at moderate intensity on a cycle ergometer, about 70% of VO2max for 60 minutes a day, 5 days a week, for 6 weeks. VO2max rose from 53 to 58 ml/kg/min, and anaerobic capacity did not change significantly. The other group, seven people, trained five days a week for six weeks with seven to eight sets of 20 seconds at about 170% of VO2max, with 10 seconds of rest. The abstract calls the training exhaustive. In that group VO2max rose by 7 ml/kg/min and anaerobic capacity by 28%.
What this means: one small study, on a bike, with very high intensity. It does not say 20/10 beats other ratios, and it does not tell you what a bodyweight version at ordinary effort would do. The abstract does not describe who the participants were beyond their number.
30/30. A 1999 conference abstract by Billat and colleagues (Medicine and Science in Sports and Exercise, supplement) had nine long-distance runners alternate 30 seconds at their velocity at VO2max with 30 seconds at 50% of it. It reports more time spent at VO2max, and lower blood lactate, than a continuous run. That is a finding about running intervals in distance runners, not about gym exercises, and it did not test other ratios.
40/20 and 45/15. We did not find a study that tests these ratios against others. They appear to be coaching habits. They are popular because the cycle is a round minute, not because anyone has shown they win. That does not make them wrong, only unproven.
Where does that leave you? With a decision you make yourself, by feel, using the guidance below.
Match the ratio to the exercise
The exercise changes what rest you need more than the label does.
- Big, fast moves (jump squats, burpees, sprints) tire you quickly. Short rest, such as 15 seconds, turns each round into a different, harder workout. These are high-impact: if you are new, scale them (step-backs instead of burpees, a brisk walk or march instead of sprints) and use 30/30 before 40/20.
- Simple, low-skill moves (marching, step-ups, bodyweight squats) can go with 45/15 once you are fit.
- Technical or loaded lifts need form. Tired reps are sloppy reps, so give yourself more rest, or fewer rounds.
- Static holds (planks) are hard to judge. A 40-second plank is a long time for a beginner, so 30/30 is kinder.
If you mix exercises in a session, you can vary the ratio too. Hard moves first with longer rest, simple moves at the end with shorter rest.
How many rounds and how long a session
Rounds multiply the cycle: 8 rounds of 40/20 take 8 minutes; 10 rounds of 30/30 take 10. Work out the time with (work + rest) times rounds.
| Ratio | Rounds | Block length | Work time |
|---|---|---|---|
| 20/10 | 8 | 4:00 | 2:40 |
| 30/30 | 10 | 10:00 | 5:00 |
| 40/20 | 8 | 8:00 | 5:20 |
| 45/15 | 6 | 6:00 | 4:30 |
Group blocks together with a longer break, such as two minutes, between them. A session of two or three blocks plus a warm-up is a full workout for most people. These numbers are examples to show the arithmetic, not prescriptions. Warm up first, and stop if something hurts. If you have a health condition, or have not exercised in a long time, ask a clinician before starting hard intervals.
Set it in a timer
Whatever ratio you choose, a timer needs four fields: work, rest, rounds, and a prep countdown. The guide to setting an interval timer on iPhone or Android has the steps and two worked examples. If you train with music, read the Spotify guide first.
Setting this in Countcall
In Countcall, the quick timer takes work, rest, rounds and sets, so you can try 30/30 this week and 40/20 next without rebuilding anything. Classic Tabata is a one-tap preset. The voice calls out the seconds and the work and rest phases as you go. The app is not in the stores yet; join the waitlist below and we will email you once when it is.
Questions people ask
Is 40/20 better than 30/30?
We found no study that compares 40/20 with 30/30 head to head, so nobody can say it is better. 40/20 gives you more work and less rest in each round, which makes each round harder and the whole session more tiring for the same length. That is a reason to choose it, or not.
What is the Tabata ratio?
Twenty seconds of work, ten seconds of rest, eight rounds, which takes four minutes. It comes from a 1996 study in which people trained on a stationary bike at about 170 percent of their VO2max.
Is 45/15 too hard?
It is hard because the rest is short. Fifteen seconds is enough to get into position and take a breath or two, not to recover. It suits low-skill exercises you can do while tired, such as marching or squats, and less so a technical lift.
How long should a HIIT session be?
There is no single correct length. We found no researched standard for session length. What matters is whether you can keep the work intervals honest from the first round to the last.
Should I do the same exercise every round?
You can. Either works. Repeating one exercise concentrates the load on the same muscles, so it usually feels harder, and moving between different exercises spreads it around.