Wake up refreshed — calculate your ideal bedtime or wake time
Each 90-minute cycle progresses through these stages:
| Age Group | Recommended | Cycles |
|---|---|---|
| Newborn (0-3 mo) | 14-17 hrs | — |
| Infant (4-11 mo) | 12-15 hrs | — |
| Toddler (1-2 yr) | 11-14 hrs | — |
| Preschool (3-5 yr) | 10-13 hrs | — |
| School (6-12 yr) | 9-12 hrs | 6-8 |
| Teen (13-17 yr) | 8-10 hrs | 5-7 |
| Adult (18-64 yr) | 7-9 hrs | 5-6 |
| Older Adult (65+) | 7-8 hrs | 4-5 |
Our calculator uses the 90-minute sleep cycle model. A full sleep cycle lasts about 90 minutes, and waking up between cycles (in light sleep) makes you feel refreshed. We calculate optimal wake times by adding 5-6 complete cycles plus 15 minutes to fall asleep.
A sleep cycle is a progression through the stages of sleep: light sleep, deep sleep, and REM sleep. One full cycle takes about 90 minutes. Most people need 5-6 cycles (7.5-9 hours) for optimal rest.
Adults need 7-9 hours of sleep per night (5-6 sleep cycles). Teens need 8-10 hours, and children need 9-12 hours. The calculator shows times for 4-6 cycles so you can choose what works for your schedule.
Waking up in the middle of a deep sleep cycle causes grogginess (sleep inertia). Timing your wake-up to the end of a 90-minute cycle can help. Our calculator finds wake times that align with the end of complete cycles.
To wake at 6 AM, go to bed at 10:45 PM (6 cycles), 12:15 AM (5 cycles), or 1:45 AM (4 cycles). The 10:45 PM bedtime gives you 7.5 hours and 5 full cycles — the recommended amount for most adults.
The average person takes about 14-15 minutes to fall asleep. Our calculator adds 15 minutes to account for this. If you typically fall asleep faster or slower, you can adjust the fall-asleep time in the settings.
Sleep has 4 stages: N1 (light sleep, 1-5 min), N2 (deeper sleep, 10-25 min), N3 (deep/slow-wave sleep, 20-40 min), and REM (dreaming, 10-60 min). A complete cycle through all stages takes about 90 minutes.
You can partially recover from sleep debt by sleeping longer on weekends, but it doesn't fully erase the effects of chronic sleep loss. The best approach is consistent sleep and wake times, even on weekends — within a 30-minute window.
Sleep inertia is the groggy, disoriented feeling you get when waking up during deep sleep (N3 stage). It can last 15-60 minutes. Waking at the end of a sleep cycle (in light N1 or N2 sleep) minimizes sleep inertia.
The 90-minute cycle is an average — individual cycles range from 70-120 minutes. The calculator provides a useful starting point, but you may need to adjust by 10-15 minutes based on how you feel. Track your sleep for a week to find your personal cycle length.