😴
Sleep Calculator
Find best bedtime or wake time based on sleep cycles
Mode
Using your current time as the reference. Hour/minute/AM-PM inputs are ignored.
Period
Bedtimes to wake at 07:00 AM
Go to sleep at one of these times
Sleep at a green or blue time to wake feeling refreshed. Each cycle is ~90 minutes.
Frequently Asked Questions
How many sleep cycles do I need?
Most adults need 5–6 complete cycles (7.5–9 hrs) per night. Athletes or those recovering may benefit from 6 cycles (9 hrs).
Why is 7 hrs worse than 7.5 hrs?
7 hours cuts mid-cycle, waking you from deep sleep. 7.5 hours (5 full cycles) ends right at the boundary — you wake up feeling natural and alert.
What is sleep inertia?
The groggy, disoriented feeling when woken mid-cycle (especially from deep sleep). It can last 15–60 minutes. Cycle-aligned waking eliminates this.
Can I use this for naps?
Yes! Aim for 20 minutes (power nap, before deep sleep) or a full 90 minutes (one complete cycle). Avoid 30–60 min naps — they often end in deep sleep.