Sleep Calculator
When to go to bed for your alarm, or when to wake for your bedtime, as a short window that fits whole sleep cycles and the time you take to fall asleep.
Key facts
- Sleep runs in cycles of light, deep and dreaming (REM) sleep: the first lasts about 70 to 100 minutes, later ones about 90 to 120.
I want to know
I usually fall asleep in
Age
More options90-minute cycles
90 suits most people. Cycles run about 70–100 minutes early in the night and 90–120 later (Carskadon and Dement).
To wake at 7:00 am, be in bed
11:10–11:20 pm
5 cycles, about 7 h 30 min asleep: recommended for adults (7–9 hours). Falling asleep in 10–20 minutes is built in.
Illustration: dashed, falling asleep; each dip, one cycle (numbered). Deep sleep comes mostly in the first cycles, dreaming sleep in the last.
- 6 cycles · 9 h
- 9:40–9:50 pm
- 4 cycles · 6 h (short)
- 12:40–12:50 am
- 3 cycles · 4 h 30 min (short)
- 2:10–2:20 am
General information from published research, not a diagnosis or medical advice. Talk to a doctor before changing medication or treatment. If you often wake unrefreshed after enough hours, snore loudly or struggle to stay awake by day, talk to a clinician. Terms
Every option4 windows, from 4 h 30 min to 9 h asleep
| Cycles | Asleep | In bed | For your age |
|---|---|---|---|
| 6 | 9 h | 9:40–9:50 pm | recommended |
| 5 | 7 h 30 min | 11:10–11:20 pm | recommended |
| 4 | 6 h | 12:40–12:50 am | short |
| 3 | 4 h 30 min | 2:10–2:20 am | short |
How much sleep by ageThe National Sleep Foundation’s ranges (2015)
| Age | Recommended a day |
|---|---|
| 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 children (6–13 years) | 9–11 hours |
| Teenagers (14–17 years) | 8–10 hours |
| Young adults (18–25 years) | 7–9 hours |
| Adults (26–64 years) | 7–9 hours |
| Older adults (65 years and over) | 7–8 hours |
How this works: Method, 4 sources, Checked against 7 worked examples,
How this works
Method
Wake-up times are your bedtime plus the time you take to fall asleep plus whole sleep cycles of about 90 minutes; bedtimes work the same way back from an alarm. Your fall-asleep range makes each answer a window, widened to whole five minutes. The suggested window is the number of cycles closest to the middle of the National Sleep Foundation’s range for your age.
Sources
- Normal human sleep: an overview (Carskadon and Dement), in Principles and Practice of Sleep Medicine (Elsevier, 2011)
- National Sleep Foundation’s sleep time duration recommendations: methodology and results summary (Hirshkowitz et al.) (Sleep Health, 2015)
- Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and SRS (Watson et al.) (J Clin Sleep Med, 2015)
- Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals (Ohayon et al.) (Sleep, 2004)
How it’s tested
7 worked examples for this page are checked by automated tests before every release: given the inputs, the tool must show the expected answer.
Limits
General information from published research, not a diagnosis or medical advice. Talk to a doctor before changing medication or treatment. If you often wake unrefreshed after enough hours, snore loudly or struggle to stay awake by day, talk to a clinician.
Changes
- First published: bedtimes and wake-up times as windows from 90-minute cycles and your own time to fall asleep, checked against the recommended sleep for your age.
Why whole cycles
Through the night you move from light sleep into deep sleep and then into REM, the dreaming stage, and start again: one full round is a sleep cycle. The first is usually 70 to 100 minutes long and later ones 90 to 120, so 90 minutes is a fair middle. Deep sleep is concentrated in the first cycles and REM in the last ones, which is why the drawing gets shallower towards morning.
Being woken from deep sleep is what leaves people groggy, and the end of a cycle is the lightest point. Planning around whole cycles is a way of aiming your alarm at a lighter moment. It is a rule of thumb, not a guarantee: your own cycles vary from night to night.
Why the answer is a window
Two things make an exact minute meaningless. Nobody knows the minute they fall asleep, and cycles aren’t all 90 minutes. So the calculator uses your own fall-asleep range (under 10, 10 to 20 or 20 to 30 minutes) and gives you the span it implies, rounded out to whole five minutes. Any time inside it is as good as any other.
If you often wake groggy at the end of a window, try moving it 15 minutes either way for a week, or change the cycle length under More options: someone whose cycles run 100 minutes will feel the difference after five of them.
How much sleep, by age
The number of cycles matters more than hitting one exactly. The suggestion is the option closest to the middle of the National Sleep Foundation’s range for your age: five cycles (7½ hours) for most adults, six (9 hours) for teenagers, seven (10½ hours) for children 6 to 13. Fewer cycles are shown too, honestly labelled as short. For babies and toddlers, whose cycles are shorter and whose sleep is spread across the day, a cycle calculator doesn’t apply.
Sources
- Carskadon and Dement, Normal human sleep: an overview, in Principles and Practice of Sleep Medicine, 5th edition (Elsevier, 2011)
- Hirshkowitz et al., National Sleep Foundation’s sleep time duration recommendations (Sleep Health, 2015)
- Watson et al., Recommended amount of sleep for a healthy adult: a joint consensus statement of the AASM and SRS (J Clin Sleep Med, 2015)
- Ohayon et al., Meta-analysis of quantitative sleep parameters from childhood to old age in healthy individuals (Sleep, 2004)
Frequently Asked Questions
How does a sleep calculator work?
It counts back from your alarm (or forward from your bedtime) in whole sleep cycles of about 90 minutes, and adds the time you take to fall asleep. Waking at the end of a cycle, when sleep is lightest, tends to feel easier than being pulled out of deep sleep.
What time should I go to bed to wake up at 7 am?
If you fall asleep in 10 to 20 minutes: between 11:10 and 11:20 pm for five cycles (7½ hours asleep), or 9:40 to 9:50 pm for six (9 hours). Five cycles sits inside the 7 to 9 hours recommended for adults.
Is a sleep cycle always 90 minutes?
No. The first cycle of the night is often 70 to 100 minutes and later ones 90 to 120, and they vary between people and nights. That is why the answer is a window, and why you can change the cycle length under More options.
How long should it take to fall asleep?
It varies with age and the night; studies of healthy sleepers find it usually takes longer as people get older. Pick the range that sounds like you. If falling asleep is a struggle most nights, or you lie awake for long stretches, a clinician can help.
Can I make up for short sleep with naps or weekends?
Partly, at best. The recommendations are about regular sleep night after night, and a short night now and then is normal. If you are regularly short, a consistent bedtime that gives you enough cycles is the change this calculator can help with.