Health · unique
Sleep Calculator
Wake up between sleep cycles, not in the middle of one.
Why sleep cycles matter
Sleep runs in cycles of about 90 minutes. Waking at the end of a cycle — rather than in the deep middle — helps you feel refreshed instead of groggy. This tool assumes about 15 minutes to fall asleep and counts back or forward in 90-minute cycles, showing the times that land you at the end of a cycle. Most adults feel best with 5 to 6 cycles a night.
Questions
How many hours of sleep do I need?
Most adults need 7 to 9 hours, which is about 5 to 6 full 90-minute cycles. The tool highlights options in that range.
Why do I wake up tired after 8 hours?
You may be waking in the middle of a deep cycle. Aligning your wake time to the end of a cycle can help you feel more rested.
Is 90 minutes exact for everyone?
No, cycles vary from roughly 80 to 110 minutes. Ninety minutes is a widely used average, so treat these as helpful guides.