Sleep Cycle Calculator
Bedtimes that land on your alarm in whole ninety-minute sleep cycles, whole-night options listed best first, with next-day options when you name a target wake time.
Fill in the values and calculate
The form sends itself back to this page — results print below, computed on the server.
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About Sleep Cycle Calculator
Sleep research counts nights in ninety-minute cycles rather than hours: waking at a cycle boundary means you are far less likely to cut a run in half. Every bedtime here lands on your alarm exactly on such a boundary.
Enter a target wake-up time and the table also prints what you would get by aiming for that instead, so you can see whether the alarm forces an early bedtime or whether moving the alarm wins cycles for free.
Questions about Sleep Cycle Calculator
Why ninety minutes and not just 'go to bed early'?
A night is a run of these cycles; waking mid-cycle often lands you stiff or half-awake, while waking at a boundary is a clean exit.
Can the bedtime be before midnight?
Yes. Bedtimes earlier than your alarm cross midnight and are labelled as being on the evening before.
What if my target time is also on a boundary?
Then the target rows repeat the plan for waking at the target, and the gap card shows the distance between the two alarms.
Bookmark and homescreen
- Press Ctrl+B now (or Cmd+B on macOS) to bookmark this page in your browser.
- Drag this link to your bookmarks bar and it will always open this tool: Sleep Cycle Calculator.
- On a phone: open in Chrome/Safari and use "Add to Home Screen" — the site ships a homescreen icon and manifest, so it installs like an app.
- Two addresses work:
https://useful-utilities.com/sleep-cycle-calculator/andsleep-cycle-calculator.useful-utilities.com. Copy whichever you prefer.