Sleep Calculator
Calculate the best times to go to bed or wake up based on 90-minute sleep cycles. Waking between cycles helps you feel more alert and refreshed.
I need to wake up at this time — when should I go to bed?
The average person takes 10-20 minutes to fall asleep. Default is 15 minutes.
Frequently Asked Questions
What is a sleep cycle and how long does it last?
A sleep cycle is a repeating pattern of brain activity that lasts approximately 90 minutes. Each cycle includes four stages: N1 (light sleep, 1-5 minutes), N2 (deeper light sleep, 10-60 minutes), N3 (deep slow-wave sleep, 20-40 minutes), and REM sleep (10-60 minutes). The composition of each cycle changes throughout the night — earlier cycles have more deep sleep, while later cycles have more REM sleep. Waking up at the end of a complete cycle, during lighter sleep, helps you feel more refreshed (Source: American Academy of Sleep Medicine, National Sleep Foundation).
How many hours of sleep do adults need?
The American Academy of Sleep Medicine (AASM) and the National Sleep Foundation recommend 7-9 hours of sleep per night for adults aged 18-64, and 7-8 hours for adults 65 and older. Teenagers (14-17) need 8-10 hours. Consistently sleeping fewer than 6 hours per night is associated with increased risks of obesity, diabetes, cardiovascular disease, depression, and impaired cognitive function. Individual sleep needs can vary, but fewer than 7 hours is generally insufficient for most adults (Source: AASM Guidelines 2023, CDC Sleep and Sleep Disorders).
Why do I feel groggy even after 8 hours of sleep?
Feeling groggy after a full night of sleep — called sleep inertia — often happens when your alarm wakes you during deep sleep (N3) or REM sleep rather than at the end of a complete cycle. Other factors include inconsistent sleep schedules, sleep disorders like sleep apnea, alcohol or caffeine consumption before bed, exposure to blue light from screens, and sleeping in a room that is too warm. Using a sleep cycle calculator helps you time your alarm to coincide with the end of a cycle, reducing sleep inertia (Source: National Institutes of Health, Harvard Medical School Division of Sleep Medicine).
Is this sleep calculator a substitute for medical advice?
No. This calculator is an educational tool that provides general guidance based on average sleep cycle durations. It is not a diagnostic tool or a substitute for professional medical advice. Individual sleep cycles can range from 70 to 120 minutes, and many factors affect sleep quality. If you regularly experience difficulty falling asleep, staying asleep, or feeling unrested despite adequate sleep duration, consult a healthcare provider or a board-certified sleep medicine specialist. Conditions such as insomnia, sleep apnea, restless leg syndrome, and narcolepsy require professional evaluation and treatment (Source: American Academy of Sleep Medicine).