90-Minute Deep Work Timer (Ultradian Rhythm)

This page opens the timer set to 90 minutes of work and a 20-minute break — a completely different model from the Pomodoro Technique, built around the body's natural ultradian rhythm rather than an arbitrary clock interval. Research into sleep and alertness cycles found that the brain moves through roughly 90-minute waves of higher and lower energy and focus throughout the day, whether you are asleep or awake.

Instead of fighting that cycle with frequent short interruptions, this method works with it: you commit to one deep, unbroken block of concentration for the length of a full ultradian wave, then take a real 20-minute recovery break before your energy naturally dips — walking, resting your eyes, stepping outside — rather than pushing through a low point at your desk.

This preset suits work that actively resists being chopped into 25-minute pieces: writing that needs to hold a whole argument in mind, deep coding sessions, studying dense material, or any task where re-entering the mental state after an interruption costs more time than the interruption saves. If your work is made of small, interruptible tasks instead, the classic 25/5/15 preset will usually serve you better.