Sleep Calculator
Calculate optimal bedtime and wake-up times based on 90-minute sleep cycles. Wake up refreshed by timing your sleep correctly.
Understanding Sleep Cycles
Quality sleep isn't just about hours -- it's about timing. Your sleep occurs in 90-minute cycles, and waking up at the end of a complete cycle helps you feel refreshed and energized, rather than groggy and disoriented.
What Are Sleep Cycles?
A sleep cycle lasts approximately 90 minutes and consists of different stages:
- Light Sleep (N1): Transition from wakefulness to sleep
- Light Sleep (N2): Most of your sleep time, body temperature drops
- Deep Sleep (N3): Physical recovery, immune system strengthening
- REM Sleep: Mental recovery, memory consolidation, dreaming
How Much Sleep Do You Need?
Sleep needs are measured in complete cycles rather than arbitrary hours:
| Sleep Cycles | Total Hours | Best For | Sleep Quality |
|---|---|---|---|
| 6 cycles | 9 hours | Young adults, recovery periods | Excellent |
| 5 cycles | 7.5 hours | Most adults (recommended) | Optimal |
| 4 cycles | 6 hours | Minimum for basic function | Adequate |
Why 7.5 Hours Is the Sweet Spot
Five complete sleep cycles (7.5 hours) provides the optimal balance for most adults:
- Adequate deep sleep for physical recovery
- Sufficient REM sleep for mental restoration
- Practical for most work schedules
- Prevents oversleeping and circadian disruption
The Science Behind Sleep Timing
Sleep inertia -- that groggy feeling when you wake up -- occurs when you're awakened during deep sleep phases. By timing your wake-up to the end of a cycle (during lighter sleep), you can minimize grogginess and feel more alert.
Fall Asleep Time
Our calculator includes a 14-minute buffer for falling asleep, which is average for healthy adults. If you consistently take longer than 20 minutes to fall asleep, consider:
- Going to bed 30 minutes earlier
- Creating a relaxing bedtime routine
- Avoiding screens 1 hour before bed
- Keeping your bedroom cool (65-68°F/18-20°C)
Optimizing Your Sleep Schedule
Consistency is key. Once you find your optimal sleep times:
- Stick to the same schedule, even on weekends
- Create a 30-60 minute wind-down routine
- Expose yourself to bright light in the morning
- Avoid caffeine 6 hours before bedtime
- Keep your bedroom dark, quiet, and cool
Common Sleep Mistakes
- Focusing on hours instead of cycles: 8 hours might be worse than 7.5 hours if it disrupts your cycles
- Weekend sleep-ins: Sleeping 2+ hours later disrupts your circadian rhythm
- Irregular bedtimes: Your body needs consistency to maintain proper sleep-wake cycles
- Using snooze buttons: These interrupt sleep cycles and increase grogginess
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Aggiornato Febbraio 2026 · Testati e verificati
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Frequently Asked Questions
What time should I go to bed to wake up at 7 AM?
To wake up at 7 AM feeling refreshed, go to bed at: 9:46 PM (9 hours), 11:16 PM (7.5 hours), or 12:46 AM (6 hours). Most people feel best with the 11:16 PM bedtime for 7.5 hours of sleep.
Why do I wake up tired after 8 hours of sleep?
You're likely waking up mid-cycle during deep sleep. 7.5 hours (5 complete cycles) often feels better than 8 hours because you wake at the end of a cycle rather than interrupting one.
How many sleep cycles do I need?
Most adults need 5-6 complete sleep cycles (7.5-9 hours). Five cycles is the sweet spot for most people -- enough for recovery without oversleeping and disrupting circadian rhythms.
Is 6 hours of sleep enough?
Six hours (4 cycles) is the minimum for basic function, but most adults need 7.5 hours for optimal cognitive performance, immune function, and overall health. Use 6 hours only when necessary.
Should I use the snooze button?
Avoid snoozing! It interrupts your sleep cycles and increases grogginess. Instead, set your alarm for the end of a complete cycle so you wake up naturally during lighter sleep.
What if I can't fall asleep at my calculated bedtime?
Create a wind-down routine starting 30-60 minutes before bed: dim lights, avoid screens, try reading or meditation. If you can't sleep within 20 minutes, do a quiet activity until sleepy.
How does shift work affect sleep cycles?
Shift workers should still aim for complete 90-minute cycles, regardless of when they sleep. Use blackout curtains and consistent timing relative to your work schedule.
Can I train myself to need less sleep?
No. Sleep needs are largely genetic and cannot be trained away. Chronic sleep restriction impairs cognitive function, immune system, and long-term health, even if you feel adapted.
Why do I feel more tired after 9 hours than 7.5 hours?
Oversleeping can disrupt your circadian rhythm and cause sleep inertia. Your body performs best with consistent cycle timing rather than simply maximizing hours.
How do naps affect my sleep schedule?
Short naps (20 minutes) won't affect nighttime sleep. Longer naps or those after 3 PM can interfere with your natural sleep cycles and make nighttime sleep more difficult.
Should children use the same sleep calculator?
Children and teenagers need more sleep cycles than adults. Teens need 8-10 hours (5-7 cycles), while younger children need even more. The 90-minute cycle principle still applies.
How accurate is this calculator?
The calculator is based on average 90-minute cycles and 14-minute fall-asleep time. Individual cycles can vary ±15 minutes, so use this as a starting point and adjust based on how you feel.