Sleep Time Calculator
Find the best bedtimes or wake times based on 90-minute sleep cycles.
Times shown in green give you 5–6 complete sleep cycles (7.5–9 hours), the ideal amount for most adults. Waking at the end of a cycle, rather than in the middle of deep sleep, helps you feel more refreshed.
How Sleep Cycles Work
Sleep is not a uniform state. Over the course of a night you move through repeated sleep cycles, each lasting roughly 90 minutes. A single cycle progresses through light sleep, deep (slow-wave) sleep, and finally REM sleep, the stage most associated with dreaming. A typical night contains four to six of these cycles.
The reason this calculator targets multiples of 90 minutes is simple: if your alarm goes off in the middle of deep sleep, you are likely to wake up groggy and disoriented, a feeling known as sleep inertia. Waking near the end of a cycle, when you are already in lighter sleep, makes the transition to being awake far smoother.
The calculator also adds about 15 minutes to account for the time it takes the average person to actually fall asleep after getting into bed. You can adjust this value if you tend to drift off faster or slower.
Recommended Sleep by Age
Sleep needs change throughout life. The following ranges are based on guidelines from the National Sleep Foundation.
| Age group | Recommended sleep |
|---|---|
| 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 |
| Adults (18–64 years) | 7–9 hours |
| Older adults (65+ years) | 7–8 hours |
Sleep Hygiene Tips
Going to bed at the right time helps, but good sleep also depends on your habits and environment. A few practices that consistently improve sleep quality:
- Keep a consistent schedule, going to bed and waking up at the same time every day, including weekends.
- Avoid caffeine and large meals in the late afternoon and evening.
- Reduce screen exposure for at least 30–60 minutes before bed; blue light suppresses melatonin.
- Keep your bedroom cool, dark, and quiet.
- Reserve your bed for sleep so your brain associates it with rest.
- Get natural daylight during the day to support a healthy circadian rhythm.
- If you can't fall asleep after about 20 minutes, get up and do something calming until you feel sleepy.
Note: This calculator uses an average 90-minute sleep cycle and a 15-minute sleep-onset estimate. Actual cycle length varies from person to person and from night to night (typically 70–120 minutes). Use the suggested times as a helpful guideline rather than a strict rule, and pay attention to how rested you feel.