Calculate optimal wake-up or bedtime based on 90-minute sleep cycles. Waking up between cycles helps you feel refreshed.
This calculator is a reference tool based on the general 90-minute sleep cycle. Actual sleep cycles vary based on age, health, fatigue, caffeine intake, and sleep environment. If you suspect a sleep disorder, please consult a healthcare professional. This calculator does not replace medical diagnosis or treatment.
"If I Sleep Now" calculates optimal wake-up times from the current time. "I Need to Wake At" calculates optimal bedtimes for your target wake time. "I'll Sleep At" calculates wake times for a specific bedtime.
Enter your bedtime or wake time depending on the selected mode. You can also adjust the time to fall asleep (default 14 minutes). What matters is when you actually fall asleep, not when you get into bed.
Six recommended times are shown with their cycle count. Times highlighted in green (5-6 cycles / 7.5-9 hours) are optimal for adults. Waking at the end of a sleep cycle helps you feel refreshed.
A sleep cycle is a repeating pattern of approximately 90 minutes during sleep. You typically go through 4-6 cycles per night. Each cycle consists of 4 stages: Stage 1 (N1) - Falling Asleep: Lasts about 5 minutes. A transitional period where you drift in and out of sleep. Easily awakened. Stage 2 (N2) - Light Sleep: Lasts about 25 minutes. Body temperature drops and heart rate slows. Makes up about 50% of total sleep. Stage 3 (N3) - Deep Sleep: Lasts about 35 minutes. Slow-wave sleep crucial for physical recovery and growth hormone release. Waking during this stage causes severe grogginess (sleep inertia). REM Sleep: Lasts about 25 minutes. The brain is highly active and dreams occur. Important for memory consolidation and learning.
National Sleep Foundation recommended sleep durations: Newborns (0-3 months): 14-17 hours Infants (4-11 months): 12-15 hours Toddlers (1-2 years): 11-14 hours Preschoolers (3-5 years): 10-13 hours School-age (6-13 years): 9-11 hours Teenagers (14-17 years): 8-10 hours Young adults (18-25): 7-9 hours Adults (26-64): 7-9 hours Older adults (65+): 7-8 hours In sleep cycles, 5 cycles (7.5 hours) to 6 cycles (9 hours) is optimal for adults. Sleeping 4 cycles (6 hours) or less can lead to chronic sleep deprivation.
Best practices for quality sleep: 1. Maintain regular sleep-wake times: Going to bed and waking at the same time daily, even on weekends, supports your circadian rhythm. 2. Limit blue light before bed: Blue light from screens suppresses melatonin production. Reduce screen use at least 1 hour before bed. 3. Limit caffeine: Caffeine has a half-life of 5-6 hours. Avoid coffee, tea, and energy drinks after 2 PM. 4. Optimize sleep environment: Dark, quiet, and cool (64-68°F / 18-20°C) is ideal. Consider blackout curtains, earplugs, or white noise machines. 5. Exercise regularly: Regular exercise improves sleep quality. However, avoid vigorous exercise within 3 hours of bedtime. 6. Establish a bedtime routine: Activities like reading, meditation, or stretching signal your brain that it's time to sleep.
90 minutes is an average. Actual cycles range from 80-120 minutes depending on the individual. Also, deep sleep (N3) decreases and REM sleep increases as the night progresses. This calculator uses the 90-minute average and doesn't account for individual variation.
Waking at the end of a sleep cycle (during the N1-N2 transition) feels most refreshing. Waking during deep sleep (N3) causes sleep inertia, making you groggy and tired. Using this calculator's recommended times helps you wake at cycle endpoints. Smart alarm apps can also help.
Optimal nap lengths are 20-25 minutes (power nap) or 90 minutes (one full cycle). Naps of 30-60 minutes may leave you groggier due to waking during deep sleep. Avoid napping after 3 PM as it may affect nighttime sleep.
While weekend catch-up sleep helps short-term, chronic sleep debt cannot be fully repaid by sleeping in. Oversleeping on weekends can cause 'social jet lag,' making Monday adjustment difficult. Consistent daily sleep schedules are most effective.
Sleep research shows healthy adults take an average of 10-20 minutes to fall asleep. 14 minutes is the midpoint of this range. Falling asleep in under 5 minutes may indicate sleep deprivation, while taking over 30 minutes could suggest sleep onset insomnia. You can adjust this to match your experience.
Yes, deep sleep (N3) decreases with age while light sleep increases. After age 60, N3 may drop below 10% of total sleep. Melatonin production decreases, leading to earlier sleep-wake times. Nighttime sleep also tends to become more fragmented.