90 minute timer
Timer
1:30:00
Ends with a chime
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What fits in 90 minutes
Ninety minutes is one long deep-work block, the length often linked to a roughly 90-minute rest-activity cycle first described in sleep research. Whether that cycle governs focus while awake is debated, but it is a practical length for:
- A serious writing session, from blank page to a rough draft.
- A hard programming problem, including the time to get into it.
- A full mock exam.
- Studying a difficult topic with active recall at the end.
Day math: two 90-minute blocks with a 15-minute break fill a morning of 3 hours 15 minutes; three with breaks make a strong five-hour day.
90/15 intervals
Switch to 90/15 at the top of the page: 90 minutes of focus, then a 15 minute break.
90/15 mode: 90 minutes of focus, then a 15-minute break away from the screen, on repeat. It suits writing, coding and research, where the first half hour is just getting into the problem. Two or three blocks make a strong deep-work day.
- Plan the block: one outcome you want in 90 minutes.
- Silence notifications and put your phone in another room.
- Start the timer, with brown noise or rain if the room is noisy.
- If you stall, switch to a smaller part of the task instead of leaving the block.
- Take the whole 15-minute break, then decide whether to do another block.
Ultradian rhythm: what we know
The 90-minute block is usually traced to sleep researcher Nathaniel Kleitman, who proposed a "basic rest-activity cycle" of roughly 90 minutes (about 80 to 120) and suggested that it continues during the day (Kleitman, 1982; overview). Productivity writers later turned this into advice to work in 90-minute blocks.
What is well documented: in sleep, non-REM and REM stages repeat as a cycle that starts over every 80 to 100 minutes, usually four to six times a night (NHLBI).
What is not: researchers argued as early as 1977 that there was no evidence of such a cycle outside sleep; later analyses suggest waking ultradian rhythms do exist but work through different mechanisms than the sleep cycle (overview). No study shows that 90-minute work blocks are the best length. Use 90 minutes because long tasks need long blocks, not because your brain runs on a 90-minute clock. If you drift after 40 minutes, start with the 50/10 timer.
Want breaks built in?
The closest interval method is the 52/17 timer: 52 minutes of focus, then a 17 minute break, on repeat.
See every timer and method, or set any length you like.
Other lengths
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Questions
About the 90 minute timer. Missing something? Write to contact@novasouds.se.
Yes. Switch this timer to 90/15 mode for a 15-minute break after each 90-minute block. The section below explains what research on the 90-minute cycle does and does not show.
Something that asks nothing of you: slow ambient music, brown noise or rain at low volume. Anything with lyrics or sudden changes is more likely to pull you out of the work.