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Sleep Calculator
Best times to go to bed or wake up in 90-minute sleep cycles, and how much sleep your age group needs.
Calculated in your browser – nothing you enter is sent or stored.
Waking up groggy even after a full night? Timing may be the problem. This sleep calculator finds the best times to go to bed for when you need to wake up – or the best times to wake up if you go to bed now – based on 90-minute sleep cycles, plus the time it takes to fall asleep. It also lists how much sleep each age group needs.
How to Use the Sleep Calculator
- Choose Wake up at and enter your alarm time to get bedtimes, or Go to bed at / Sleep now to get wake-up times.
- Adjust time to fall asleep – most people take 10–20 minutes.
- If you know your cycles run shorter or longer, change the cycle length.
The green times give 5 or 6 complete cycles – 7½ to 9 hours of sleep, which fits the recommendation for adults.
How Sleep Cycles Work
During the night you move through repeating cycles of about 80–100 minutes, usually 4–6 a night. Each cycle has light sleep (stages N1 and N2), deep sleep (N3) and REM sleep, when most dreaming happens. Deep sleep is concentrated early in the night and REM sleep later. Waking from deep sleep often causes "sleep inertia" – that heavy, foggy feeling – so waking near the end of a cycle, in light sleep, usually feels easier.
Example: to wake at 6:30 AM with 90-minute cycles and 15 minutes to fall asleep, go to bed at 9:15 PM (6 cycles, 9 hours) or 10:45 PM (5 cycles, 7½ hours). 12:15 AM gives only 4 cycles – 6 hours – which is less than most adults need.
How Much Sleep Do You Need?
| Age | Recommended sleep per day |
|---|---|
| 4–12 months | 12–16 hours, including naps |
| 1–2 years | 11–14 hours, including naps |
| 3–5 years | 10–13 hours, including naps |
| 6–12 years | 9–12 hours |
| 13–18 years | 8–10 hours |
| 18–60 years | 7 or more hours |
| 61–64 years | 7–9 hours |
| 65 and older | 7–8 hours |
About one in three U.S. adults regularly gets less than the recommended amount, according to the CDC.
Tips for Better Sleep
- Keep a consistent schedule, even on weekends – your body clock adjusts to regular times.
- Get morning daylight and dim the lights and screens in the hour before bed.
- Keep your bedroom cool, dark and quiet; many people sleep best around 65°F.
- Limit caffeine after early afternoon and avoid heavy meals and alcohol close to bedtime.
- Talk to a doctor if you snore loudly, stop breathing during sleep or feel tired despite enough time in bed – these can be signs of sleep apnea or another sleep disorder.
Sources
- CDC – About sleep (how much sleep do I need?)
- NIH NINDS – Brain basics: understanding sleep
- American Academy of Sleep Medicine – Sleep Education
Last reviewed: October 2026 by the ShrinkBee team. This page is for general information and is not medical advice.
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