Sleep Calculator
Find the best bedtime or wake time based on 90-minute sleep cycles. Avoid grogginess and track your sleep debt.
Enter how many hours you slept each of the last 7 days to calculate your sleep debt and recovery time.
Answer 5 questions to discover if you're a morning person, evening person, or somewhere in between.
How Sleep Cycles Work
Understanding your sleep architecture helps you wake up feeling refreshed.
90-Minute Cycles
Sleep follows 90-minute cycles through light, deep, and REM stages. Waking mid-cycle causes sleep inertia. Waking at cycle end feels natural and refreshing.
5 or 6 Cycles
Most adults need 5 cycles (7.5 hours) or 6 cycles (9 hours). Teens need more. Our calculator adjusts recommendations based on your age group.
Sleep Debt
Missing sleep accumulates as debt. Each hour lost takes about 1.3 days to recover. Track your debt and plan your recovery with our calculator.
Frequently Asked Questions
Common questions about sleep cycles, debt, and chronotypes.
Sleep cycles last approximately 90 minutes. Waking in the middle of a cycle leaves you groggy, while waking at the end leaves you refreshed. This calculator finds bedtimes or wake times aligned with natural cycle completion.
Most adults need 5-6 cycles (7.5-9 hours). Teenagers need 8-10 hours. Adults 18-64 need 7-9 hours. Adults 65+ need 7-8 hours. The calculator uses age-based NSF recommendations.
Sleep debt is the cumulative hours of missed sleep. Recovery takes about 1.3 days per hour of debt. Recover by going to bed 15-30 minutes earlier each night and maintaining a consistent wake time.
Your chronotype determines whether you are naturally a morning person, evening person, or somewhere in between. Our 5-question quiz helps identify your chronotype so you can align your sleep schedule with your natural rhythm.
Yes! Waking at the end of a 90-minute sleep cycle dramatically reduces grogginess. That's why waking at 6:00 AM might feel better than 6:30 AM, even though it is earlier.