Interval timer: the work/rest guide

An interval timer is a clock that runs a schedule you set once: a countdown to the start, a work length, a rest length, a number of rounds. After you press start, it counts you in, opens the work, ends it with a cue, runs the rest whether you feel finished or not, and stops after the last round. The counting and the switching move over to the app and stay there for the whole session.

Every session built this way, from a four-minute Tabata to a twelve-round fight night, rests on the same four numbers. Prepare is the time between pressing start and the first effort. Work is the length of one effort. Rest is the gap before the next one. Rounds is how many times the pair repeats. Stack a 10-second prepare, 20 of work and 10 of rest eight times over and you have Tabata, the most cited four minutes in conditioning research. Swap the middle numbers to 180 and 60 and you have boxing rounds, with a bell at each boundary.

A stopwatch could time all of that, in principle, if you were willing to watch it for the whole session and do the arithmetic between efforts. In practice the glancing eats the workout, because the person doing burpees is a poor clockkeeper. An interval timer takes the schedule out of your hands, which is the point of the tool. This guide covers the territory: what the four numbers do, how to pick them for a goal, what the timer should do while it runs, and where each subtopic opens into a longer piece.

Contents

• The four numbers
• Picking the numbers for the goal
• When one block is not the whole session
• What you hear while it runs
• How the timer behaves while you train
• Phone, watch, wall or web
• The interval timer library
• Where Intertakt stands
• Questions people ask

The four numbers

Prepare, ten seconds by default, exists so that the first effort does not begin with the phone still in your hand. It is the number nobody bothers to set and the first one you notice when it is absent: the session opens with a scramble from the coffee table to your marks, and the first round suffers for it.

What work costs depends on the movement. Twenty seconds of burpees and twenty seconds of air squats are the same number with two different bills, and when a session feels wrong, the work length is the first number to interrogate. Too long, and quality dies somewhere in the middle rounds; too short, and the session never demands enough for the body to adapt. Lengths are whole seconds, which matters more than it sounds: a protocol that needs 35 seconds of work does not have to round anywhere, and odd intervals are ordinary intervals.

The body does its adapting between efforts, so rest deserves as much programming as the work. It can be standing, walking, shaking the arms out; it can even change across a session, with a longer break every few rounds to keep the late rounds worth counting. Those schemes have their own piece on round rest.

With rounds you set the volume. Add rounds and the session simply lasts longer at the same intensity; take rounds away and the session is shorter, which on a crowded Tuesday is a useful thing to be able to do. The original Tabata protocol runs eight, boxing runs three-minute rounds in threes, and most general conditioning sits between four and twelve.

Around the four numbers sit two edges that are easy to skip: what you do before prepare, and what happens after the last bell. A warm-up that ramps, a cool-down that actually runs, and how the whole arc fits into one uninterrupted session are laid out in the full-session guide from warm-up to cool-down. The four numbers inside it stay the same.

Picking the numbers for the goal

There is no universal best ratio, because the ratio is doing different jobs for different goals.

For general conditioning, the working band is 1:2 to 1:1, work to rest, with efforts of 20 to 40 seconds. Both famous fixed points live in that band: Tabata’s 20/10, which is 2:1 and four minutes of genuinely hard work, and the friendlier 40/20, which most people can finish on a flat week. The comparison between the two is worth reading before committing to either, since the demands are different even when the numbers look close together.

Strength and power, loaded or bodyweight, want the ratio flipped: short efforts, 10 seconds or so, against long rest, 50 to 90 seconds, so that every effort starts fresh. Cutting the rest to make the session feel harder converts it into conditioning, which is a legitimate goal that works better when chosen deliberately.

If you are new to intervals, start around 1:3, something like 20 seconds of work against 60 of rest, and move up when the last round has looked like the first for a week straight. The full progression logic, one dial per week, is in the piece on the work-to-rest ratio and intensity.

Once work stretches into whole minutes, the problem shifts from surviving the interval to spending it well. That is a pacing problem, and pacing long intervals covers it. Short days keep every rule above at a third of the length, and ten-minute HIIT formats exist for exactly that.

When one block is not the whole session

A circuit with different movements usually wants different clocks, or at least different labels: 30 seconds of squats, 20 of push-ups, 40 of mountain climbers, each with its own rest, walked through as a list. That is per-exercise programming, and it turns the timer from a metronome into something more like a coach, one that calls the next exercise by name.

The named formats on gym whiteboards are all translations of the same four fields. EMOM makes the round a minute and hands you the remainder as rest. AMRAP is one long work block with a hard zero at the end. For Time runs the clock the other way. Tabata is the 20/10 pair again. Each format has its own psychology, and the protocol piece walks through all four; for choosing between the CrossFit staples specifically, EMOM versus AMRAP compared is the deeper cut.

Runners arrived at the same idea decades earlier with fartlek, speed play, where the intervals are felt rather than fixed; how fartlek relates to HIIT maps the overlap. The structure also works outside sport entirely. Forty-five minutes of work against fifteen of rest is a focus cycle with a real bell at each end, argued for in 45/15 focus cycles.

What you hear while it runs

During a hard interval you are not looking at the screen, so the timer speaks to you in sound, and the choice of sounds decides how much of the session reaches you. Beeps do the boundaries, short and bright, the ear picks them out of any mix. A bell earns its place at endings, above all the final one, which arrives when you are most spent. Voice is different in kind, because it can carry words: the count-in and count-out, the round you are in, the name of what comes next. Choosing between these for a specific room, a garage, a shared gym, headphones, is its own short guide.

None of it works if the cue cannot ride over whatever is playing, so music and cues need separate volume, a mechanism with practical settings for a loud gym. What the voice itself should sound like, and why so many app voices grate after a week, is covered in what a timer voice should sound like. If your background audio is an audiobook, the stakes are different and so are the settings; cues over audiobooks and podcasts keeps the chapter alive.

How the timer behaves while you train

The numbers can be perfect and the session still dies on a phone quirk, so this is the part worth checking before you trust an app with weeks of your programming.

Your audio keeps playing. The most common pre-purchase question in the whole category is whether the timer will kill the music. It should not, and if yours does, the cause and the fix are in why interval timers stop your music.

The screen can go dark. A session run by ear needs no screen, and the phone in a pocket with the display asleep should keep counting; training screen-off builds that habit. If you want the display lit and it sleeps anyway, the Android and iPhone settings that matter are untangled in the screen-timeout fix.

It survives interruptions without lying about them. A call comes in mid-round; the timer pauses, then resumes where the round stood, without quietly shortening the rest or losing the count. What honest resume means, and how to test for it, is in interruptions and honest resume. Before any of that, it should stop asking you things mid-set: permissions, ratings, tips, anything with a dialog.

It counts true. A timer that loses a second per round changes your program without telling you. Where drift comes from, and how much accuracy is reasonable to expect, is the subject of timer drift and background kills.

You can read it from where you are. Phase and round, both legible in one glance from across the room, is the whole argument of what round am I on.

It remembers your work. The sessions you build should live under names you chose: presets that never disappear, and, when the phone changes, a real way to move presets between phones.

Phone, watch, wall or web

The clock app already on your phone has countdowns, so it is fair to ask what an interval timer adds. Mostly, structure: sixteen hand-set countdowns for one Tabata, against one saved session started with a tap. The full case runs the math.

Watches time intervals poorly for reasons of their own, mostly wrist ergonomics mid-movement, and watch versus phone timing names the places the wrist falls apart. A phone can also be more than a phone: propped on a tripod, cast to the garage TV, it becomes the wall clock you already know how to use, which is the any-screen argument and, for dedicated hardware shoppers, the wall-clock-versus-phone question.

What the category looks like right now, where the paywalls sit, which apps are weekend clones, and what a free timer should cost you, is surveyed in the 2026 field guide to interval timer apps, with the free-tier specifics in what free interval timers actually take and the quality tells in a solid timer versus a weekend clone.

The interval timer library

Every topic above has a dedicated piece. Grouped by what you are trying to do:

Protocols and structures. The formats and the programming logic: Tabata against 40/20, the original 20/10 protocol, EMOM versus AMRAP, all four whiteboard protocols built from the same fields, fartlek versus HIIT, the work-to-rest ratio, pacing long intervals, rest between rounds, odd intervals in whole seconds, a full session from warm-up to cool-down, per-exercise programming, ten-minute HIIT workouts, the beep test run at home, and 45/15 focus cycles.

Sports and disciplines. The same fields, tuned per sport: boxing rounds at home, kettlebell swing intervals, kettlebell GS sets on the minute, hangboard repeaters for climbers, rebounder intervals, the garage CrossFit session, cold immersion rounds, desk-break complexes, and interval timing beyond fitness.

Reliability and behavior. What the timer does when you are not looking: music that keeps playing, drift and background kills, interruptions and honest resume, permission prompts that stay out of the way, the screen-timeout fix, reading the round from across the room, presets that never disappear, and moving presets between phones.

Cues and sound. What to listen for in voice cues, what a timer voice should sound like, beeps over loud music, bell, beep or voice for your room, and why hands-free is not voice control.

Devices and alternatives. The clock app compared, watch versus phone, wall clocks versus the phone you own, any screen as a gym timer, what free timers take, a solid timer versus a weekend clone, screen-off training, and the 2026 app field guide.

What plays while you train. Audiobooks and podcasts alongside the cues, and running the session over your own music.

Where Intertakt stands

Intertakt is the timer this guide describes. Whole-second work, rest, prepare and rounds, saved as named presets that autosave on every change; per-exercise lists where the session needs them; voice cues in English, Russian and Spanish that call boundaries, rounds and the next exercise; beeps that ride over your music at their own volume; a screen that can go dark with the session still counting; pause and resume that keep the round’s place. The core timer is free, with unlimited sessions and no ads. Premium is a one-time purchase in the app that removes the saved-plan cap and adds session history with JSON export.

Intertakt is out on Google Play. If you want one email when the iOS version lands, leave your address on the waitlist.

Questions people ask

Is an interval timer just a stopwatch with extra steps?

Time one Tabata with a stopwatch and you will find out inside the first two minutes: you end up doing the timer’s job, watching the count and starting each rest and each work burst, all while doing burpees. An interval timer takes the scheduling off you.

Will it stop my music?

It should not. In a timer built for intervals, cues and music run on separate volume, so a beep or a voice can sit over the track or under it without pausing playback. Apps that cut your audio on every cue are solving their own engineering problem at your expense.

Do I need an account to use one?

No. An account adds nothing here: the four numbers and the session list live fine on the device, with an export file as the backup. Two things are worth checking before you invest an evening of programming: whether presets live on the device, and whether an export path exists so the library can come with you.

Can each exercise have its own time?

In a full-featured interval timer, yes. The session is a list, each line with a name, a work length and a rest length, and the voice can call the next movement so the order survives a foggy round. Timers that only take one global pair of numbers hit their ceiling on circuits first.

Does the screen have to stay on?

With a timer that runs in the background, no. Start the session, put the phone face-down or in a pocket, and work by ear. On Android, one battery setting decides whether that works reliably, and it wants checking once. On iPhone it mostly works out of the box, and the display-sleep question only matters if you want the screen visible from across the room.

What is the first session to try?

A 1:3 starter, twenty seconds of work against sixty of rest, eight rounds, ten-second prepare, three movements you already know rotated through. It fits inside a bad day, and the last two rounds will tell you whether 1:3 is right for your current fitness. After that, move one number at a time.