How it works
Sleep runs in cycles of roughly 90 minutes. Waking at the end of a cycle, rather than in the middle of deep sleep, can help you feel more alert. Adults generally need 7 or more hours a night; teenagers need more.
Consistency matters more than any single night: try to keep the same wake-up time every day, including weekends. Read our sleep guide for habits that help.
Frequently asked questions
How many hours of sleep do adults need?
Most adults need at least 7 hours of sleep a night. Regularly sleeping less is linked to weight gain, high blood pressure, diabetes and poor mood.
Note: This tool gives general estimates for healthy adults. It is not medical advice or a diagnosis. Talk to a doctor about your own results.