Ultradian Rhythm Timer: 90-Minute Focus Cycles
Ninety minutes of deep work, then twenty minutes of real rest. Preset and ready — press Start.
This timer keeps its own settings, separate from the main Pomodoro timer. Your tasks and stats are shared.
What the ultradian rhythm is (and isn’t)
At night, your sleep runs through cycles of light, deep and REM sleep that last about 90 minutes each. In the 1960s Nathaniel Kleitman suggested that a similar “basic rest-activity cycle” keeps ticking through the day, with alertness rising and dipping. Productivity writers took that idea and turned it into a work schedule: 90 minutes on, then a proper break.
Be honest with yourself about the evidence. Daytime ultradian cycles are real in some measurements but far less regular than sleep cycles, and they vary from person to person. The 90-minute block works mostly because it is long enough for deep, uninterrupted work and short enough that most people can keep their attention for it.
Making a 90-minute block work
- Protect it. Phone in another room, notifications off, door closed if you can.
- Front-load your hardest work into the first block of the day.
- Take the 20 minutes seriously; a walk beats scrolling.
- If you notice your attention sagging well before 90 minutes, that’s your signal. Try Flowtime to measure your natural span.
Questions
What is the ultradian rhythm?
Ultradian rhythms are biological cycles shorter than a day. The best known is the roughly 90-minute cycle of sleep stages, described by sleep researcher Nathaniel Kleitman. Kleitman proposed a similar “basic rest-activity cycle” continues while we are awake.
Is there proof we focus in 90-minute cycles?
The evidence for a fixed 90-minute cycle of alertness during the day is mixed. Sleep cycles are well established; daytime cycles vary a lot between people and studies. The popular 90-minute work block owes as much to K. Anders Ericsson’s research on expert musicians, who practised in sessions of up to about 90 minutes, as to biology.
How long should the break be?
Advocates usually suggest 15–20 minutes of genuine rest: walking, a snack, lying down. This timer uses 20 minutes.
How many 90-minute blocks can I do?
Two to four is a realistic day. Ericsson’s violinists rarely did more than about four hours of deliberate practice a day.