FREE TOOLS
45/15 interval timer
45 seconds of work, 15 seconds of rest, with a beep at every change, free in your browser
How to use it
- Pick 8, 10 or 12 rounds, or set your own.
- For a circuit, repeat the rounds as blocks with a rest between them, under Warm-up, cool down and blocks.
- Press Start: three short beeps warn you before each change.
Why 45/15?
With three times as much work as rest, 45/15 is one of the harder common formats. The 15 seconds are just enough to change exercise or station, so it’s often used for circuits and conditioning classes. If your form slips late in the session, move to 40/20.
| Rounds | Work | Rest | Total |
|---|---|---|---|
| 8 | 6:00 | 1:45 | 7:45 |
| 10 | 7:30 | 2:15 | 9:45 |
| 12 | 9:00 | 2:45 | 11:45 |
Workout ideas
- Circuit: 6 stations, twice through, with a minute of rest between rounds.
- Kettlebell: swings, goblet squats, presses and rows.
- Core: planks, dead bugs and side planks, one per round.
Questions
Is 45/15 harder than 40/20?
Usually, yes: 5 more seconds of work and 5 fewer of rest in every round, for almost the same total time. Try 45/15 when 40/20 starts to feel easy.
How many rounds of 45/15 should I do?
8 to 12 rounds is a common range, as on the HIIT timer page. Warm up first, and stop when your form breaks down.
YOUR NEXT SESSION STARTS HERE
Bring the effort.
We’ll keep the time.
Cero is free to download for iPhone, iPad and Apple Watch.
Download Cero
Cero is a timer, not a medical device. If you’re new to hard exercise, are pregnant or have a health condition, check with your doctor first, and stop if you feel unwell.