General guidance based on average 90-minute sleep cycles, not medical advice. Talk to a doctor about ongoing sleep problems.
This sleep calculator tells you what time to go to bed or when to wake up so that you finish a full sleep cycle instead of waking in deep sleep. It counts 90-minute cycles plus the time you take to fall asleep. It also plans naps and shows your weekly sleep debt against the recommended hours for your age.
How to use
- Bedtime: enter when you need to wake up. You get bedtimes that end on a full sleep cycle; the highlighted one gives 5 or 6 cycles.
- Wake up: tap Now (or enter a bedtime) to see alarm times that fall between cycles.
- Set Time to fall asleep to how long you usually lie awake. Most people need 10–20 minutes. It is remembered.
- Nap: pick a nap length to see when to set the alarm, and start a nap timer in one tap.
- Sleep debt: choose your age group and enter last week’s hours. You see the gap to the recommended amount and how to make it up.
- A sleep cycle averages about 90 minutes, but it ranges from roughly 70 to 120 minutes between people and through the night. Treat the times as a starting point and adjust by 10–15 minutes.
- Recommended sleep by age, from the National Sleep Foundation (Hirshkowitz et al., 2015): newborns 0–3 months 14–17 h; infants 4–11 months 12–15 h; toddlers 1–2 years 11–14 h; preschoolers 3–5 years 10–13 h; school age 6–13 years 9–11 h; teens 14–17 years 8–10 h; young adults 18–25 years and adults 26–64 years 7–9 h; older adults 65+ 7–8 h.
- Naps: 10–20 minutes refreshes without grogginess. 30–60 minutes can leave you groggy for a while. 90 minutes is a full cycle and is best taken early in the afternoon.
- Sleep debt cannot be fully repaid in one weekend. Adding 15–60 minutes a night over several nights works better than one very long sleep.
- Your inputs stay on this device. Settings are saved in your browser only.
How sleep cycles work
During the night you pass through light sleep, deep sleep and REM sleep several times. One cycle averages about 90 minutes, though it ranges from roughly 70 to 120 minutes between people and through the night. Most adults get four to six cycles, which is 6 to 9 hours.
Waking at the end of a cycle tends to feel easier than being pulled out of deep sleep. Treat the suggested times as a starting point and shift them by 10–15 minutes until mornings feel right.
How much sleep you need
The National Sleep Foundation (Hirshkowitz et al., 2015) recommends 14–17 hours for newborns, 9–11 hours for children aged 6–13, 8–10 hours for teens aged 14–17, 7–9 hours for adults aged 18–64 and 7–8 hours from age 65. Regular bed and wake times matter as much as the total.
This is general guidance, not medical advice. Talk to a doctor about ongoing insomnia, loud snoring or daytime sleepiness. Your inputs stay on this device.
Frequently asked questions
What time should I go to bed to wake up at 6:30?
With 15 minutes to fall asleep, aim for 21:15 (six cycles), 22:45 (five cycles) or 00:15 (four cycles). Five cycles, 7.5 hours, suits most adults.
How long is a sleep cycle?
About 90 minutes on average, but it varies from about 70 to 120 minutes. Cycles early in the night have more deep sleep, later ones more REM.
Is it better to sleep 6 or 7.5 hours?
7.5 hours, five full cycles, is closer to the 7–9 hours recommended for adults. Six hours regularly is short sleep for most people.
How long should a power nap be?
10–20 minutes. You wake before deep sleep, so you feel refreshed rather than groggy.
Can I catch up on lost sleep at the weekend?
Only partly. Adding 15–60 minutes a night over several nights works better than one very long lie-in, which can shift your body clock.