What does this tool do?
Sleep cycles last around 90 minutes, and most people take 10–20 minutes to fall asleep. This calculator subtracts full cycles plus a falling-asleep allowance from your wake time to suggest a bedtime.
The Formula
Bedtime = Wake time − (Cycles × 90 min + Fall-asleep minutes)Frequently Asked Questions
Why use 90-minute cycles?
Ninety minutes is a common average, but cycles vary between about 70 and 120 minutes and change through the night. Use the result as a starting point and adjust by how you feel.
Does the bedtime need to be exact?
No. A window of 15–30 minutes around the suggested time is usually enough. Consistency matters more than hitting an exact minute.