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Sleep Calculator
Bedtimes and wake times that land between sleep cycles.
Best times to go to bed
Each of these lands the alarm at the end of a full cycle rather than in the middle of deep sleep.
How much sleep do you need?
| Age group | Recommended | Cycles |
|---|---|---|
| Newborn (0–3 months) | 14–17 hours | — |
| Infant (4–11 months) | 12–15 hours | — |
| Toddler (1–2 years) | 11–14 hours | — |
| Preschool (3–5) | 10–13 hours | — |
| School age (6–13) | 9–11 hours | 6–7 |
| Teen (14–17) | 8–10 hours | 5.5–6.5 |
| Adult (18–64) | 7–9 hours | 5–6 |
| Older adult (65+) | 7–8 hours | 5–5.5 |
Why cycle timing matters
A full sleep cycle runs roughly 90 minutes through light sleep, deep sleep and REM. Waking at the end of one is noticeably easier than being pulled out of deep sleep partway through — that grogginess is sleep inertia, and it can last 15 to 30 minutes. It is also why a shorter sleep ending on a cycle boundary can leave you feeling better than a longer one that does not.
Best bedtime
—
Details
Sleep duration—
Complete cycles—
Time in bed—
Deep sleep (approx.)—
—
Against the 7–9 hour adult recommendation
Cycle length varies between people and lengthens through the night, so treat these times as a starting point rather than a schedule. Consistently falling asleep in under five minutes suggests real sleep deprivation; taking over thirty may indicate insomnia.
Quick Tool Overview
The Sleep Calculator finds bedtimes and wake times that fall between 90-minute sleep cycles, so the alarm catches you at a light stage rather than pulling you out of deep sleep. It allows about 15 minutes to fall asleep.
- What it does
- Finds bedtimes and wake times aligned to sleep cycles
- You give it
- A wake time, or the time you are going to bed
- You get back
- Several suggested times, each ending a full cycle
- Best for
- Shift work, early starts and waking up less groggy
About the Sleep Calculator
Work out what time to go to bed to wake at a particular hour, or what time to set an alarm if you are going to bed now, with each option lined up so the alarm falls at the end of a sleep cycle rather than in the middle of one.
A full cycle runs roughly 90 minutes through light, deep and REM sleep, and waking at the end of one is noticeably easier than being pulled out of deep sleep partway through — which is the grogginess known as sleep inertia. The calculator allows about 15 minutes to fall asleep, since that is the usual figure and forgetting it is what makes most bedtime maths wrong. Cycle length does vary between people, so treat the times as a starting point.
Key features of the Sleep Calculator
Works both directions
Wake at a set time, or go to bed now and find the best alarm times.
Sleep onset allowed for
About 15 minutes to fall asleep is built in — the step most bedtime maths forgets.
Explains sleep inertia
Waking mid-deep-sleep causes grogginess that can last 15 to 30 minutes, which is why cycle timing matters.
Several options shown
Four to six cycles, so you can pick one that fits the evening you actually have.
Honest about variation
Cycle length varies from about 70 to 120 minutes between people, and the page says so.
How to use the Sleep Calculator
-
1
Choose a direction
Wake at a set time, or go to bed now and find the best alarm times.
-
2
Enter the time
The calculator allows about 15 minutes to fall asleep.
-
3
Pick a cycle count
Five or six cycles suits most adults — 7.5 to 9 hours of sleep.
-
4
Set your alarm
Each suggested time falls at the end of a cycle rather than mid-way through one.
Frequently asked questions
About 90 minutes on average, running through light sleep, deep sleep and REM. Individual cycles vary from roughly 70 to 120 minutes, and they lengthen through the night.
Seven to nine hours for most adults, which is five to six complete cycles. Teenagers generally need eight to ten, and young children considerably more.
Usually because the alarm interrupted deep sleep rather than because the sleep was too long. That grogginess is sleep inertia, and it can last 15 to 30 minutes.
Between 10 and 20 minutes is typical. Consistently falling asleep in under five minutes suggests significant sleep deprivation; over 30 may indicate insomnia.
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