Sleep Calculator

A complete sleep cycle lasts approximately 90 minutes and includes all stages of sleep: light sleep (N1 and N2), deep sleep (N3), and REM sleep. During this cycle, your body progresses through each stage, with deep sleep occurring more in the first half of the night and REM sleep increasing in duration towards morning. Waking up at the end of a complete cycle, rather than in the middle, helps you feel more refreshed and less groggy.

Most adults need 5-6 complete sleep cycles per night, which equals 7.5 to 9 hours of sleep. However, individual needs can vary based on age, lifestyle, and overall health. Teenagers often need 8-10 hours (5-6+ cycles), while some adults function well with just 4-5 cycles. The key is consistency and waking up at the end of a cycle rather than in the middle.

Our calculator is based on the average sleep cycle duration of 90 minutes and accounts for the typical 15-minute time it takes to fall asleep. While these are scientifically-backed averages, individual sleep cycles can range from 80 to 120 minutes. The calculator provides a helpful guideline, but you may need to adjust based on your personal experience. Track how you feel when waking at different suggested times to find your optimal schedule.

Grogginess upon waking, known as "sleep inertia," typically occurs when you wake up during deep sleep (N3) or in the middle of a REM cycle. This is why timing your wake-up to coincide with the end of a 90-minute cycle can help you feel more alert. Other factors that contribute to grogginess include: poor sleep quality, sleep deprivation, sleep disorders, inconsistent sleep schedule, and dehydration. Using our calculator can help minimize sleep inertia by optimizing your wake time.

Yes! Use our Nap Timer mode for optimal napping. You have two ideal options: a 20-minute power nap (before entering deep sleep) or a full 90-minute cycle nap. A 20-minute nap provides a quick energy boost without sleep inertia, while a 90-minute nap allows you to complete a full cycle. Avoid 30-60 minute naps as these durations often leave you in deep sleep, making you feel groggy upon waking. The best time for a nap is typically between 1-3 PM, aligned with your natural circadian dip.

Yes! Maintaining a consistent sleep schedule, even on weekends, is one of the most important factors for good sleep health. Irregular sleep patterns can disrupt your circadian rhythm, leading to "social jet lag" and making it harder to fall asleep and wake up during the week. If you're sleep-deprived during the week, it's better to go to bed earlier rather than sleeping in late on weekends. Try to keep your wake time within 1 hour of your weekday schedule for optimal sleep health.

Our calculator is based on the average sleep cycle duration of 90 minutes and accounts for the typical 15-minute time it takes to fall asleep. While these are scientifically-backed averages, individual sleep cycles can range from 80 to 120 minutes. The calculator provides a helpful guideline, but you may need to adjust based on your personal experience. Track how you feel when waking at different suggested times to find your optimal schedule.

Our calculator is based on the average sleep cycle duration of 90 minutes and accounts for the typical 15-minute time it takes to fall asleep. While these are scientifically-backed averages, individual sleep cycles can range from 80 to 120 minutes. The calculator provides a helpful guideline, but you may need to adjust based on your personal experience. Track how you feel when waking at different suggested times to find your optimal schedule.