Interval timer basics: work, rest and rounds

You open an interval timer and it asks for three numbers before you've even warmed up. Those numbers are work (how long each effort lasts), rest (how long you recover) and rounds (how many times you repeat them). A safe first setting for most people is 30 seconds work, 30 seconds rest, 8 rounds, with a 5-minute warm-up before it.

In short

Work, rest and rounds are the whole idea. Add a warm-up before and a cool-down after.

Start with numbers you can finish with good form. Change one number at a time.

If you can't hear the beep in a loud gym, use a timer that changes the whole screen colour and vibrates.

1. What do work, rest and rounds mean?

Most interval timers ask for the same three things:

Work: how long each hard effort lasts, such as 30 seconds of jogging or 40 seconds of squats.
Rest: how long you recover before the next effort. Rest can be walking, slow pedalling or standing still.
Rounds: how many times you repeat one work spell and one rest spell.

So "30/30 × 8" means 30 seconds work, 30 seconds rest, 8 times. That's 8 minutes.

Some timers also have a warm-up before the first round, a cool-down after the last, and labels for each round, such as "squats" or "press-ups".

2. What numbers should I start with?

There's no single right answer. These are sensible starting points, from us:

Session	Work	Rest	Rounds	Total
First walk-run on a treadmill	60 s jog	90 s walk	6	15 minutes
General fitness, bodyweight	30 s	30 s	8	8 minutes
Fitter, mixed circuit	40 s	20 s	10	10 minutes
Tabata	20 s	10 s	8	4 minutes
Rowing or bike intervals	60 s	60 s	6 to 10	12 to 20 minutes

Add a 5 to 10 minute warm-up before any of these, and a few minutes of easy movement after.

For walk-run detail, see treadmill interval workouts for beginners. For the 20/10 format, see what a Tabata workout is.

3. How hard should the work spells be?

Use the talk test. The NHS describes it like this:

Moderate: you can still talk, but not sing.
Vigorous: you can't say more than a few words without pausing for breath.

For most interval sessions, work spells should feel vigorous, and rest spells should bring you back to moderate or easier.

The UK Chief Medical Officers' guidelines describe HIIT as very vigorous activity in short bursts with breaks in between. You don't have to start there. A brisk walk with short jogs is interval training too.

4. How long should the rest be?

Long enough that the next round is still good quality.

A rough guide:

Rest longer than work (such as 30 s work, 60 s rest) for very hard efforts like sprints, or if you're new.
Rest equal to work (30/30) for most people starting out.
Rest shorter than work (40/20, 45/15) once you're fitter, or for steady circuit work.

If the last two rounds fall apart, make the rest longer before you cut the work. If it feels easy, add a round before you make the work longer.

Lifting weights rather than doing intervals? That's a different question. See how long to rest between sets.

5. How many rounds should I do?

Fewer than you think, at first.

Pick a number you're confident you can finish. Eight rounds of 30/30 is plenty for a first session. You can always add rounds next time.

A simple way to progress, one change a week:

Add a round or two.
Then add 5 to 10 seconds to the work.
Then shorten the rest a little.

Never change all three at once.

6. What's the difference between interval formats?

The names on gym whiteboards are just different ways of setting the same three numbers:

HIIT: any short, hard efforts with rest. Numbers vary.
Tabata: 20 seconds work, 10 seconds rest, 8 rounds.
EMOM: a set number of reps at the start of every minute; the rest is whatever's left of the minute.
AMRAP: one long block of work, as many rounds as possible, with rest only when you need it.
Circuits: one work-and-rest cycle at each station, then move on.

More in Tabata vs HIIT and EMOM vs AMRAP.

7. What if I can't hear the beep?

Gyms are loud, and headphones or hearing aids aren't always an option.

Look for a timer that:

changes the whole screen colour for work and rest, so you can read it from across the room
shows big numbers
vibrates at each change, so you can feel it in a pocket or armband
still works with the phone locked

Test it at home with the sound off before you rely on it. Our guide to interval timer apps for deaf and hard of hearing gym-goers goes into more detail.

8. Should I write it down?

Yes. Note the numbers and how the last round felt, in a word or two. Next time you'll know where to start, and over a few weeks you'll see the progress.

If you have a heart condition, are pregnant, are recovering from an injury or illness, or haven't exercised for a long time, speak to your GP before starting hard interval sessions.

How Reptyl helps

Reptyl Timer is our interval timer for iPhone.

Your own timers. Set work, rest, rounds and labels, and keep them for next time.
Ready-made timers. Treadmill sessions such as 30/30, a pyramid and 4 × 4, plus Tabata, EMOM and plank sets.
Colour and a buzz. Every change fills the screen with colour and buzzes the phone. Sound is optional.
Carries on if the app closes. Lock the phone and it still buzzes at each change. If iOS closes the app, the run opens again at the right point.

It's a one-off purchase with no subscription, no account and no adverts, and your data stays on your phone. The Timer page has the details.

Quick answers

What does 30/30 mean on an interval timer?

30 seconds of work, then 30 seconds of rest, repeated for the number of rounds you set.

How many rounds should a beginner do?

Around 6 to 8 rounds of a short format such as 30/30 is plenty to start. Add a round or two each week if it feels manageable.

Should rest be longer than work?

For very hard efforts or if you're new, yes. For most steady sessions, equal work and rest is a good start. Fitter people often use less rest than work.

Do I need a warm-up before intervals?

Yes. Five to ten minutes of easy movement, building up, makes the first hard round much less of a shock.

Want a timer you can see and feel? See Reptyl Timer