How the sleep calculator works
Sleep runs in cycles of roughly 90 minutes, moving through light sleep, deep sleep and REM (dreaming). Waking at the end of a cycle usually feels easier than being pulled out of deep sleep. Most adults need 5 or 6 cycles: 7.5 or 9 hours. The calculator counts back (or forward) whole cycles and adds the time it takes you to fall asleep.
How much sleep do you need by age?
| Age | Recommended sleep per 24 hours |
|---|---|
| Infant 4–12 months | 12–16 hours (incl. naps) |
| Toddler 1–2 years | 11–14 hours (incl. naps) |
| Preschool 3–5 years | 10–13 hours (incl. naps) |
| School age 6–12 | 9–12 hours |
| Teen 13–18 | 8–10 hours |
| Adult 18–60 | 7 or more hours |
| Adult 61–64 | 7–9 hours |
| 65 and older | 7–8 hours |
Tips for better sleep
- Keep the same wake-up time every day, including weekends.
- Get daylight in the morning, and dim the lights and screens in the hour before bed.
- Avoid caffeine in the 6 hours before bed and large meals late at night.
- Keep the bedroom cool, dark and quiet.
Cycle length varies from person to person (about 70–120 minutes), so treat these times as a starting point. If you snore loudly, stop breathing at night or feel tired after enough sleep, talk to a doctor.
More: how much sleep do I need?
Sleep Calculator FAQs
What time should I go to bed if I wake up at 6 AM?
For 6 cycles (9 hours) fall asleep at 9:00 PM; for 5 cycles (7.5 hours) at 10:30 PM. With 15 minutes to fall asleep, get into bed at 8:45 PM or 10:15 PM.
Is 6 hours of sleep enough?
For most adults, no. The CDC recommends at least 7 hours. Six hours is 4 full cycles, which may feel better than 6.5 hours but still leaves you short over time.
What time should a teenager go to bed?
Teens need 8–10 hours. For a 6:30 AM wake-up, that means asleep between about 8:30 and 10:30 PM.
Why do I wake up tired after 8 hours?
You may be waking mid-cycle, sleeping poorly (noise, alcohol, late caffeine) or have a sleep disorder. Try timing your sleep with the calculator for a week.