Free · work/rest rounds · loud cues
Interval timer for HIIT and circuits
Set your work and rest lengths, pick the round count, and go. The display flips between red work and green rest with a chime at every switch, audible from across the room.
Describe the session, get the structure
Pro turns constraints into a work/rest/round structure and loads it straight into this timer. Say how long you have, what you have, and what you cannot do.
Example · “20 minutes, no equipment, quiet enough for an upstairs flat”
Quiet flat circuit
40s on · 20s off · 20 rounds≈ 20 min
- Squat to chair
- Incline press-up
- Reverse lunge
- Dead bug
- Glute bridge
Twenty rounds of 40 on, 20 off is 20 minutes exactly. Every move stays on the floor, so nothing thuds through to the flat below.
Form on the lunges is the first thing to go once you are tired — drop to a shorter range rather than pushing through.
What is a good work to rest ratio?
It depends what you are training. Roughly 1:1, like 40 seconds on and 40 off, suits general conditioning and lets most people hold form across the whole session. Pushing to 2:1 or 3:1 work-heavy makes it a lactate session and the last rounds will be noticeably worse than the first, which is the point. Going the other way, 1:2 or 1:3 with long rests is for genuine power work where each effort should be fresh.
The mistake most people make is picking a ratio that looks impressive and then quietly reducing effort to survive it. A shorter work interval you attack properly beats a long one you jog through.
What is the difference between HIIT and Tabata?
Tabata is one specific protocol: 20 seconds of genuinely maximal work, 10 seconds rest, eight rounds, four minutes total. It came out of a study on speed skaters and the intensity is the whole design. HIIT is the general family that Tabata belongs to, covering anything that alternates hard efforts with recovery, which is why HIIT sessions vary from 30 seconds to several minutes per interval.
In practice, most things sold as Tabata are HIIT with a 20/10 clock. That is fine, but it is not the protocol, and the difference matters if you are following the research rather than the branding.
How do I plan an interval workout?
Work backwards from the constraints rather than the exercises: how long you have, what equipment is in the room, and what you cannot do, whether that is jumping at 6am above a neighbour or anything that loads a sore knee. The structure falls out of those, and then you fill it with movements.
Pro will do that step for you. Describe the constraints in a sentence and it returns a work, rest and round structure that fits the time you actually have, with movements chosen to respect the limits, loaded straight into this timer rather than printed for you to copy in by hand.
Will it keep time if I switch tabs?
Yes. Each phase ends at a timestamp taken from your system clock rather than by counting ticks, so a browser throttling a background tab cannot make a round run long. The remaining time and the round count also appear in the tab title, and the screen is held awake while a session runs so a phone does not lock mid-set.
Frequently asked questions
- What is the difference between HIIT, Tabata, and EMOM?
- They are all interval structures. Tabata is a fixed protocol (20 seconds work, 10 rest, 8 rounds). HIIT is the general pattern with any work/rest ratio. EMOM means 'every minute on the minute' — you start a task each minute and rest whatever remains.
- Will the chime fire if my phone screen locks?
- The timer keeps perfect time in a backgrounded tab, but browsers only play sound from pages that stay open — keep the tab visible during a workout. The screen is held awake automatically while the timer runs.
- Can I set custom work and rest lengths?
- Yes — work from 5 seconds to 10 minutes, rest from 0 to 5 minutes, up to 50 rounds. Setting rest to 0 gives you straight repeating work intervals.
- Is this free?
- Yes, fully. No account, no download, and the timer logic runs in your browser.