How to Set Up a 40/20 Interval Timer (and When 45/15 Is the Better Ratio)

You set the timer to 40 seconds on, 20 off, eight exercises, three rounds. It looks simple on paper. Then the first rest beeps, you walk to the kettlebell, chalk your hands, set your feet, and the next work interval starts while you are still bending down to pick it up.

That is the real problem with 40/20. The numbers are easy. What decides whether the session works is where the transition seconds come from, and most timers leave that entirely to you.

Why 40/20 is the default ratio

Forty seconds is long enough to get 10 to 15 good reps of almost anything, and short enough that you can keep the quality high. Twenty seconds of rest is enough to take a few breaths, not enough to fully recover. That 2:1 ratio is why bootcamps, circuit classes and most "45-minute HIIT" formats land on it.

A typical session is 8 exercises × 3 rounds, which is 24 minutes of intervals. Add a minute of rest between rounds and a 10-second prep at the start, and you have a 26-minute workout that fits comfortably in a lunch break.

Where the transition time actually goes

If every exercise happens in the same spot — burpees, squats, mountain climbers on one mat — 20 seconds of rest is genuinely 20 seconds of rest. The moment you add stations, it is not. Walking to a kettlebell, picking up dumbbells or getting onto a rower easily costs 5 to 8 seconds, so your real recovery shrinks to around 12.

You have three ways to handle that. Keep 40/20 and accept the shorter recovery, which is fine for bodyweight work in one spot. Arrange the stations so equipment sits within a step of each other, which is the cheapest fix there is. Or change the ratio so the transition gets its own time, which is where 45/15 comes in.

Whichever you choose, the 3-second countdown into each work phase matters more than it seems. It is the cue that tells you to grip the bell now, not after the beep, and it is what stops you losing the first five seconds of every interval.

When 45/15 is the better choice

45/15 is a 3:1 ratio. It is harder than 40/20 because you get 25% less rest and 12.5% more work in the same 60 seconds. It suits sessions where every exercise is in one place, where the moves are lower intensity (planks, carries, core work), or where you are fitter and 40/20 has started to feel easy.

It is the wrong choice for station circuits. Fifteen seconds of rest minus a 7-second walk leaves 8 seconds, which is not rest at all. If you want more work per minute and you are moving between stations, a better option is 40/20 with fewer stations, or 45/15 with all the equipment in a small cluster.

A good progression is to run 40/20 for three or four weeks, then switch the same exercise list to 45/15. Same length session, same exercises, more work — and an honest test of whether your fitness has moved.

Setting it up in a timer

The minimum a timer needs for this is a work duration, a rest duration and a round count. That covers a single block of 40/20. To run the full session properly you also want a longer rest between rounds, a short prep before the first interval, and a distinct sound for work versus rest so you never have to look.

In Peak Interval you set this up as one block of work and rest, repeat it for the number of exercises, then wrap it in a round count with a longer rest between rounds. Change the work interval from 40 to 45 and the rest from 20 to 15, and every interval in the session updates at once, so moving from 40/20 to 45/15 is two edits rather than forty-eight. If you want each interval to show the exercise name, or need nested blocks with different ratios in one session, see how to set up repeating sets.

On an Apple Watch the same workout runs on your wrist, with a haptic tap at each transition. That is useful in station circuits, where your phone is often on the floor across the room.

The short version

Use 40/20 when you are moving between stations or still building fitness, and plan the station layout so walking does not eat the rest. Use 45/15 when everything is in one spot or 40/20 has stopped being hard. Either way, add a 3-second countdown into work, a 10-second prep at the start, and a longer rest between rounds, so the timer handles the session and you just work.