Free 90 minute Pomodoro timer based on ultradian rhythm research. 90 minutes of uninterrupted deep work aligned to your natural brain focus cycle.
The ultradian rhythm is a 90-minute biological cycle — the same cycle that governs sleep stages also operates during waking hours. Neuroscientist Andrew Huberman and sleep researcher Nathaniel Kleitman documented that focused cognition naturally rises and falls on 90-minute cycles. Working with this rhythm, not against it, optimizes performance.
Not strictly — the traditional Pomodoro is 25 minutes. A 90-minute session is more accurately called a "focus block" or "deep work session." However, many practitioners use 90 minutes as their extended Pomodoro unit, especially for complex creative and cognitive work. The principle is the same: one session, one task, no interruptions.
A minimum 20-minute break is needed after 90 minutes of focused work. Ideally: take a walk outside (non-sleep deep rest), do light physical activity, or simply sit quietly without screens. Your brain needs genuine downtime to consolidate what you learned or created in the session.
2 blocks is sustainable for most knowledge workers (3 hours focused work + 2 × 20-min breaks = about 3.5 hours). 3 blocks approaches the top end (4.5 hours). Cal Newport suggests even elite performers rarely exceed 4 hours of genuine deep work. Quality outweighs quantity.
90-minute sessions benefit: writing long-form content, complex software architecture, strategic planning, research synthesis, creative problem-solving. Short 25-minute intervals better suit: repetitive tasks, email processing, administrative work, and tasks where regular checking is part of the workflow.