Sleep Calculator
Sleep is not uniform: it happens in cycles of about 90 minutes, each moving from light sleep into deep sleep and REM. Waking up in the middle of a cycle — during deep sleep — is what makes you feel groggy and tired, even after many hours in bed. Waking up at the end of a cycle, when sleep is lightest, makes you feel far more rested. This calculator works backwards (or forwards) from your target time, adds about 15 minutes to fall asleep, and shows you the times that land right at the end of a full cycle.
Sleep cycles last 90 minutes on average, but they vary from person to person. This is a general guide, not an exact value.
You should go to bed at one of these times:
You should wake up at one of these times:
Publicidad
How it works
The calculator assumes each sleep cycle lasts 90 minutes and that it takes about 15 minutes to fall asleep. If you set a wake-up time, it subtracts 15 minutes plus 3, 4, 5, or 6 full cycles to find good bedtimes. If you set a bedtime, it adds those 15 minutes plus 4, 5, or 6 cycles to find good wake-up times. The 5–6 cycle options (about 7.5 to 9 hours) are best for most adults.
How much sleep you need by age
How many hours you should sleep changes a lot across life. The table lists the ranges recommended by the National Sleep Foundation, based on a review of the scientific evidence. These are targets for total sleep over 24 hours (naps included for younger ages), not exact requirements — some people feel their best slightly outside their band. Use them to sanity-check the cycle-based times above: if aiming for 6 cycles pushes an adult past 9 hours every night, 5 cycles may be the better fit.
| Age group | Recommended sleep |
|---|---|
| Newborn (0–3 months) | 14–17 h |
| Infant (4–11 months) | 12–15 h |
| Toddler (1–2 years) | 11–14 h |
| Preschooler (3–5 years) | 10–13 h |
| School-age (6–13 years) | 9–11 h |
| Teenager (14–17 years) | 8–10 h |
| Adult (18–64 years) | 7–9 h |
| Older adult (65+ years) | 7–8 h |
The 90-minute sleep cycle
A night of sleep is not one long block but a repeating cycle of about 90 minutes. Each cycle climbs from light sleep (stages 1 and 2) down into deep, slow-wave sleep, then rises into REM sleep, where most dreaming happens. A healthy adult goes through 4 to 6 of these cycles per night. The catch is deep sleep: being woken from it triggers sleep inertia, the heavy, foggy grogginess that can linger for 15 to 30 minutes. Waking at the end of a cycle — when you are already in light sleep — sidesteps most of that fog, which is why the times above are spaced exactly 90 minutes apart. Individual cycles can run from roughly 70 to 110 minutes and stretch as the night goes on, so treat the result as a smart estimate rather than a stopwatch.
Publicidad
Preguntas frecuentes
- Why 90-minute cycles?
- A full sleep cycle — moving through light sleep, deep sleep, and REM — lasts about 90 minutes on average in adults. Over a night you go through 4 to 6 of these cycles. Ninety minutes is an average: individual cycles can run anywhere from about 70 to 110 minutes.
- Why do I feel worse after more hours of sleep sometimes?
- Because you probably woke up in the middle of a cycle, during deep sleep. Being pulled out of deep sleep causes grogginess (sleep inertia) that can last 15–30 minutes, even if you slept longer overall. Waking up at the end of a cycle, in light sleep, feels much easier.
- Why does the calculator add 15 minutes?
- Most people do not fall asleep the instant their head hits the pillow. The average time to fall asleep (sleep latency) is around 10–20 minutes, so the calculator adds 15 minutes so the cycles are counted from when you actually fall asleep, not from when you get into bed.
- How many cycles should I aim for?
- Most adults do best with 5 to 6 cycles per night, which is roughly 7.5 to 9 hours of sleep. Four cycles (about 6 hours) can work occasionally, but consistently sleeping that little is linked to worse health and performance.
- Is this an exact science?
- No. Cycle length varies between people and even between nights for the same person, and it can be affected by age, stress, alcohol, and sleep debt. Treat the times as a helpful guide to aim for, not a precise prescription.