90-minute work blocks and the ultradian rhythm behind your focus

a rhythm shorter than a day

most people know about circadian rhythms, the roughly 24-hour cycle that sets when we feel sleepy and when we wake up. but underneath that big daily clock, smaller and faster cycles are running all the time. these are called ultradian rhythms. the word just means "occurring more than once in a 24-hour period," and rhythms like this show up all over the body, from how some hormones are released to the contractions of the stomach muscles. most of the time we never notice them.

the one most relevant to focus is the basic rest-activity cycle, or BRAC. it was developed by the sleep researcher Nathaniel Kleitman across the 1950s and early 1960s. Kleitman noticed that sleep moves in cycles of roughly 90 minutes, with deeper sleep alternating with lighter, REM-heavy phases. then he went a step further. he proposed that this cycle of activity and rest doesn't switch off when we wake up, and that it keeps running through the day in cycles of roughly 90 to 120 minutes, nudging our energy, alertness and ability to concentrate.

if that's right, your brain isn't built for one long marathon of focus. it's closer to a series of sprints with recovery in between, a kind of internal tide chart that rises and falls whether you're paying attention to it or not.

the focus wave: peaks and dips

applied to waking hours, the idea goes like this. you get a stretch of higher alertness and sharper thinking, then a dip where your energy drops and your attention wants a rest. for many people the peak seems to last somewhere around 60 to 90 minutes, though the exact length varies from person to person and day to day.

when the dip arrives, pushing through it on willpower alone tends to give you less and less back. you make more silly mistakes. you read the same paragraph three times and take in none of it. a task that felt fine 45 minutes ago suddenly feels like climbing a mountain. it's like driving on fumes when the gas light has been on for twenty miles.

a lot of productivity advice says to grind through that feeling. the ultradian lens suggests a different reading: the slump isn't a personal failure or proof that you're lazy, it's a fairly predictable signal that a short break is due. that reframe alone can take a lot of pressure off.

is it science, or just good vibes?

it's worth being honest here. Kleitman's work on sleep cycles and the basic rest-activity cycle is well established. the leap from that to "everyone should work in precise 90-minute blocks" is not nearly as rigorously tested. much of the support for using ultradian rhythms as a productivity tool is anecdotal: people noticing patterns in their own energy and building their days around them, rather than a clinical trial proving a 90-minute peak for everyone.

that doesn't make it useless. plenty of people, including "deep work" advocates like Cal Newport, have found real value in putting their most demanding work into longer, uninterrupted blocks. a 2014 DeskTime study of highly productive employees found that the most efficient workers tended to work in sprints of about 52 minutes followed by 17-minute breaks. that isn't 90 minutes, but it's the same basic shape: focused effort, then a genuine pause.

so the takeaway isn't a magic number. it's the principle that attention comes in waves, and that figuring out what works for your brain, even from plausible personal observation, can beat waiting for a meta-analysis.

how 90-minute blocks compare to pomodoro

if this sounds familiar, it's because it shares a shape with the pomodoro technique, created by Francesco Cirillo in the late 1980s: 25 minutes of focused work, then a 5-minute break. pomodoro is a classic for good reason. it's great for breaking big tasks down and getting started, especially when procrastination feels like a heavy blanket.

but sometimes, just as you're really getting into a groove, the timer buzzes and yanks you out of it. for brains that tend toward hyperfocus, or for anyone who needs a long runway before they settle in, 25 minutes can feel like barely enough time to warm up, and the mandatory break can feel more disruptive than helpful. a longer block of roughly 60 to 90 minutes gives deeper tasks room to breathe, as long as it ends with a break that actually restores you.

neither approach is right for everyone. some people do best with 45-minute blocks, some swear by 90, and some switch depending on the task.

recognizing your own dips

working with your rhythm starts with noticing its signals. they're rarely dramatic. usually they're small nudges you've learned to ignore.

physical signs can include:

• yawning more, even when you slept fine
• fidgeting, shifting in your chair, or wanting to get up and walk around
• a sudden craving for a snack or a drink
• a general restlessness, like your body wants a change of state

mental signs can include:

• a task that felt engaging earlier now feels tedious or overwhelming
• your mind drifting into daydreams or unrelated thoughts
• rereading sentences or instructions without absorbing a word
• staring blankly at the screen, scrolling aimlessly, or jumping at every notification

none of these are moral failings or proof of a weak will. they're information. spotting them is the first step toward focus you can keep up day after day, instead of pushing until you're drained and the quality of your work slips.

how to actually use 90-minute blocks

the goal isn't to set a rigid 90-minute timer and never deviate. it's to plan around your energy and then listen to it.

start by putting your most demanding, high-focus work into the part of the day when you expect to feel sharpest. for some people that's first thing in the morning, for others it's after lunch. then commit to one extended, uninterrupted block of somewhere between 60 and 90 minutes. silence notifications, close irrelevant tabs, and dive into one significant task. a visible timer like the 90/20 focus timer can help you hold the boundary without checking the clock every few minutes, and a steady background from the noise generator can make it easier to settle in.

when your focus starts to fade, or the signs above show up, take a real break of roughly 15 to 30 minutes. then, if you feel refreshed, start another cycle. if you don't, that's useful to know too.

run the first week or two as an experiment. try different block and break lengths, and notice how you feel at the end of a block and again after the break. tailor the timing to your own rhythm rather than a universal rule.

what a real break looks like

it's easy to think any pause from work counts as a break. but checking social media, firing off a quick email reply or watching a short YouTube video still asks your brain to process, react and decide. it's a different task, not a rest, and it doesn't give your attention the reset it was asking for.

a restorative break means stepping away from mentally demanding things entirely. some options:

• take a short walk, even if it's just to another room or around the block
• stretch, or look out a window at something natural
• close your eyes for a minute
• get a glass of water, grab a snack or make a cup of tea
• have a brief, non-work chat with someone nearby
• follow a short visual breathing exercise with the breathing guide, or put on something calm from the ambient sound mixer

these breaks aren't time wasted. they're part of how you keep working well, and they mean you come back to the next block with more in the tank instead of less. think of them as an investment in your next cycle.

ultradian rhythms and ADHD brains

for a lot of people with ADHD, the idea of a neat, predictable rhythm can sound a bit optimistic. ADHD brains often keep their own time. some days that looks like hyperfocus that runs for hours past any "cycle". other days it looks like a real struggle to get started at all, where even 25 minutes feels like a stretch. against that, 90 minutes can seem like an arbitrary number when your brain is running its own wild drum solo.

so don't use the framework as a mold to force yourself into. use it as a way to observe. do you naturally settle into a groove for 75 minutes, or even two hours? do you need to reset more often than every 25 minutes, but less often than every 10? think of 90 minutes as a hypothesis to test, not a hard rule. if you're deep in focus past the 90-minute mark on work that matters, you don't have to break the flow. if you hit a wall at 45 minutes, take the break you need.

where the framework may help some people with ADHD is permission. instead of aiming for eight hours of unbroken attention (hard for almost anyone), you plan for a series of focused bursts with recovery built in. attention dips stop looking like a failure of willpower and start looking like a normal part of the day, which can take some of the guilt and frustration out of them. some people also find that planned resets keep hyperfocus from tipping into exhaustion, or keep boredom from sliding into task avoidance.

it's about adjusting your expectations to the brain you actually have. instead of one continuous beam of attention, you're working with a series of strong, well-timed flashes, with real rest in between.

beyond the clock

whether it's 25 minutes, the 52/17 split, or 90 minutes, the best focus technique is the one that works for you right now. the ultradian rhythm is simply another lens on your energy, one that moves you away from purely external timers and toward your own internal cues, and that respects your need for both concentrated work and genuine rest. sometimes the best timer is the one inside your head, telling you when to lean in, when to pull back, and when to let your mind wander for a bit.

if you're curious which focus techniques might click with your brain, try the focus quiz.