Introducing the Ultradian Flow Method

A fixed 25-minute timer treats every person, every task, and every day as identical. The same number is handed to a student memorising vocabulary, a developer holding a complex problem in their head, and someone clearing email. It is a comfortable default, but it was never tuned to anyone’s biology.

There is early evidence that the fixed schedule is not just arbitrary but actively suboptimal. In one 2025 study comparing break strategies among students, a fixed Pomodoro schedule produced faster-accumulating fatigue and a steeper drop in motivation than letting people regulate their own breaks, with no advantage in task completion^[1]. It is a single study, not the last word, but it points the same way as everything below: the rigid clock is the part worth questioning, not the idea of focused work followed by rest.

The friction worth removing, then, is the one-size-fits-all clock bolted on top of a sound idea. What should replace it is not “no structure,” but structure that fits you.

The “ultradian” in Ultradian Flow comes from the work of Nathaniel Kleitman, the founder of modern sleep science. Kleitman identified a roughly 90-minute cycle that structures our sleep, and he proposed that the same basic rest-activity cycle continues into waking life, showing up as recurring swings in alertness through the day^[2]. On this view the working day is not a flat plateau of capacity but a series of roughly 80 to 90 minute waves, with natural crests and troughs.

The crucial detail, and the one most productivity advice gets wrong, is that this cycle is not a fixed clock. Reviewing two decades of evidence, Kleitman highlighted that the waking period is “non-stationary”: it can differ between morning and afternoon, and even within a single sitting^[3]. It also varies from person to person. That is precisely why a single prescribed number, whether 25 minutes or a rigid 90, cannot match anyone’s biology for long. The honest prescription is not a magic interval but a frame you fit to yourself, and re-check as it drifts.

This is the heart of the method. Work with the wave instead of against an arbitrary clock.

The second inspiration is Tony Buzan’s work on learning, the same source Francesco Cirillo drew on when designing the Pomodoro Technique. Buzan documented that recall is not even across a session: we remember more from the beginning and the end of a learning period, and less from the long middle^[4]. This is the primacy/recency effect applied to continuous learning.

That single fact reframes what a break is. A break is not dead time. Every break creates a new “end” just before it and a fresh “beginning” just after it, and so it manufactures extra high-recall moments. Buzan put the arithmetic plainly: a single unbroken two-hour block yields two strong recall peaks, but the same two hours, split into shorter sessions with breaks, can yield eight, without adding a minute of content^[4].

There is even an honest range for how long a focused block should run. Buzan placed the sweet spot, where understanding and recall work together best, at roughly 20 to 40 minutes^[4]. The 25-minute Pomodoro sits inside that window, which is no accident given Cirillo cited Buzan^[5]. And counter-intuitively, the best moment to break is often when a session is going well: understanding stays high, but your recall of that understanding starts to fade if you never pause^[4].

So when your aim is to learn, breaks are not grudging interruptions; they are where a good chunk of the material actually gets locked in, and breaking often is the right instinct. But hold onto that condition. This is one powerful way to work, not the only one: deep, creative work has a different goal, and the method treats it differently, as the next sections show. The Ultradian Flow Method does not impose one cadence on everything; it fits the cadence to the work.

If recall is highest at the beginning and end of a session, then the best length depends on what the session is for.

For learning and revision, shorter is better. A short block, somewhere around 15 to 20 minutes, is almost all high-recall beginning and end with very little of the low-recall middle, and running several of them multiplies those strong edges rather than burying material in one long trough^[4]. Buzan’s own figures show how low you can sensibly go: across his books the recommended study block shifts around, and one edition puts the ideal as low as 10 to 45 minutes^[6]. So a 15-minute revision block is not too short; for committing things to memory, it can be exactly right.

Deep, immersive work pulls the other way. A developer, writer, or designer has to load a large mental model into their head before the real work even begins, and every interruption means rebuilding it^[7]. Here the cost of stopping early outweighs the recall benefit of frequent edges, so a longer block, an hour or more, fits the work far better. The 25-minute interval that helps a student revising vocabulary actively gets in a maker’s way.

That is why the method is built around adjustable, purpose-fit lengths rather than one universal number. It does not dictate a single cadence; it offers a menu and lets the purpose choose: a short setting for learning, a standard setting for everyday work, and a long, protected setting for deep work, each one a starting point you tune to yourself and to the day.

The “flow” in Ultradian Flow is the state of absorbed, effortless concentration that the psychologist Mihaly Csikszentmihalyi popularised as flow: the feeling of being so immersed in a task that time and self-consciousness fall away. It is where the best work tends to happen, and it is exactly what a rigid clock destroys.

The cost of breaking that focus is real and measurable. Switching away from a task leaves “attention residue,” a part of your mind still stuck on what you were doing, which competes for the resources the next task needs^[7]. A timer that yanks you out at the 25-minute mark, just as you have finally settled in, is at war with your own attention.

So the method’s job during deep work is to get out of the way. When you are in flow, it protects the run and lets you ride it to a natural boundary, rather than cutting you off at an arbitrary bell. And flow does not always announce itself in advance: sometimes a session you meant to keep short turns into real depth, and the method stays flexible enough to let that take hold rather than breaking the spell to honour a number. The break still comes, because the recovery is the point, but it arrives at a seam in the work, not in the middle of a thought.

Cirillo’s full technique is a measurement system: plan, track every interval, record it, review it, repeat. It is genuinely useful for people who want to optimise their estimates, but in practice most people only ever run the timer and skip the ledger entirely. We are not going to rebuild that mandatory paperwork.

The part that does keep people coming back is engagement: a sense of progress, momentum, and a little play. That is the third inspiration, the principles behind gamification. Streaks, gentle progress, and the satisfaction of a session well finished can carry the habit without turning focus into accountancy. This is a design intent rather than a research finding, and it is the layer we are still shaping, but the rule is simple: any stats should be there because they are motivating, never because the method demands you maintain them.

Less to do, in other words, not more. The friction Pomodoro adds is the thing we are removing; the enjoyment is the thing we want to keep.

Pulling the threads together, the Ultradian Flow Method comes down to four ideas:

• A flexible frame, not a fixed number. The ~90-minute cycle is the guide, and how you apply it flexes to the task, the day, and you. It does not have to be exact, because your biology is not exact^[3].
• Breaks that build memory, when you are learning. Recovery placed to harvest the recall peaks Buzan documented, not just to pad the clock^[4].
• Protected flow, when you are deep in the work. The method guards the run and surfaces you at a natural boundary instead of an arbitrary one, and stays flexible enough to let depth take hold when it comes.
• Engagement without friction. A light, optional layer of play, never a mandatory ledger.

The method, and an app built around it, are in active development. Because the work is led by research rather than a single clever idea, it will take time to get right, and we would rather do that than ship a stricter timer with a new coat of paint. In the meantime, the free Pomodoro timer is here today, the science series lays out the evidence in depth, and the story of how Pomodo became Bracadia is told in Pomodo is now Bracadia .