Sleep Calculator
Calculate the best time to go to bed or wake up based on 90-minute sleep cycles. Wake up refreshed instead of groggy.
Frequently Asked Questions
What is a sleep cycle?
A complete cycle of light sleep, deep sleep, and REM lasts ~90 minutes. Waking up mid-cycle causes grogginess (sleep inertia).
How many sleep cycles do I need?
Most adults need 5-6 cycles (7.5-9 hours). Teenagers need more (6-7 cycles), older adults slightly less.