The short answer
Interval training alternates periods of hard work with periods of rest. The two numbers you choose, how long you work and how long you rest, decide what kind of workout you get. Short rest compared with work keeps your heart rate high and builds fatigue fast; long rest lets you work harder in each round.
The timer below has presets for the most common formats: Tabata 20/10, EMOM 10 minutes, 30/30 for 10 rounds and a 40/20 HIIT workout with three sets. You can change every number, including the warm up, the rest between sets and the cool down.
| Format | Work | Rest | Rounds | Total work | Feels like |
|---|---|---|---|---|---|
| Tabata | 20 s | 10 s | 8 | 2 min 40 s | Very hard, short |
| 40/20 | 40 s | 20 s | 8 per set | 5 min 20 s per set | Hard, classic class format |
| 30/30 | 30 s | 30 s | 10 to 20 | 5 to 10 min | Hard but repeatable |
| EMOM | Reps at the start of each minute | Rest of the minute | 10 to 20 | Depends on reps | Self paced, strength friendly |
| Long intervals | 2 to 4 min | 1 to 3 min | 4 to 6 | 8 to 24 min | Steady, hard aerobic |
Try it here: Interval Timer
Open the full tool pageWork to rest ratio
The ratio between work and rest is the simplest way to compare formats. Tabata and 40/20 are 2 to 1: twice as much work as rest. 30/30 is 1 to 1. Sprint training often uses 1 to 3 or more, for example 15 seconds of sprinting and 45 seconds of walking, because a true sprint cannot be repeated without proper recovery.
A useful rule: if you can keep the same pace in the last round as in the first, the ratio fits the effort. If your last rounds fall apart, either slow down, shorten the work or lengthen the rest. If the last round feels as easy as the first, you can work harder or rest less.
- 2 to 1 (Tabata, 40/20): high heart rate, quick fatigue, good for short sessions.
- 1 to 1 (30/30, 60/60): sustainable for longer, good for running, rowing and bodyweight circuits.
- 1 to 2 or more: maximum efforts such as sprints, heavy kettlebell work or hill repeats.
Tabata: the four minute classic
The format comes from a 1996 study by Izumi Tabata, in which trained athletes pedalled on an exercise bike at an intensity well above what they could sustain, 20 seconds at a time with 10 seconds of rest, for eight rounds. The point of the protocol is the effort level: it only works as described if each 20 seconds is close to all out. Done with moderate effort, it is simply a short circuit.
In group classes, a Tabata is often one block of a longer session: four Tabatas with four different exercises and a minute of rest between them. On the timer, set Sets to 4 and Rest between sets to 60 seconds. The timer skips the final 10 second rest of each block, because the set break follows anyway.
EMOM: every minute on the minute
In an EMOM you do a fixed number of repetitions at the start of every minute and rest for whatever is left of that minute. If 10 kettlebell swings take 20 seconds, you rest 40; when you get tired, the swings take longer and the rest gets shorter. That self regulating effect makes EMOM popular for strength and skill work, such as pull ups, cleans or double unders.
To set it up, choose the EMOM preset or set Work to 60 seconds, Rest to 0 and Rounds to the number of minutes. The timer then beeps at the start of every minute and counts down the last three seconds, so you know when the next set begins. For alternating exercises, use even and odd rounds: push ups on odd minutes, squats on even minutes.
Longer intervals and sets
Intervals of two to four minutes at a hard but controlled pace, with one to three minutes of easy movement in between, are common in running, cycling and rowing. Four rounds of four minutes is a classic session for improving endurance. These intervals are less about fast fatigue and more about time spent close to your maximum heart rate.
Sets help to structure longer workouts. Instead of 24 rounds in a row, do three sets of eight rounds with a longer break between sets. The break lets you change equipment, drink water and keep your form in the later rounds.
Warm up, cool down and safety
High intensity intervals put a lot of load on muscles, joints and the heart. Warm up for at least five minutes with easy movement and a few short, faster efforts before the first hard round, and finish with a few minutes of easy movement. The timer's Warm up and Cool down fields run these automatically, before and after the intervals.
If you are new to exercise, have a heart condition or are returning after an injury, start with longer rest, lower effort and fewer rounds, and ask a doctor or a qualified coach if you are unsure. Two or three hard interval sessions per week are plenty for most people; the rest of the week can be easier training.