Sleep Calculator
Sleep Cycle Calculator
This tool helps you figure out the best bedtime or wake‑up moment so you finish a sleep cycle feeling rested. Adjust the cycle duration or your personal sleep‑onset time in the settings.
Sleep Length Calculator
With this calculator you can determine the exact hour you should rise or hit the sheets to achieve a desired amount of sleep. If you already know your bedtime and wake‑up time, the Hours Calculator tells you how many hours you actually slept. Remember to subtract the minutes it takes you to drift off, as this varies from person to person.
Sleep is a repetitive state where both body and mind relax, muscle activity drops, interaction with the environment lessens, and responsiveness to stimuli wanes. The capacity to react distinguishes sleep from wakefulness. Here we focus on human sleep.
Sleep cycles
The sleep cycle can be defined as the oscillation between non-REM (rapid eye movement) and REM sleep, which will both be discussed below.
When we fall asleep is mainly driven by hormonal cues from our internal circadian clock. This clock keeps a steady rhythm that syncs with external cues like day and night, and it can keep ticking even when those cues vanish. Jet lag is a classic example: fast long‑distance travel throws the clock off, leaving travelers feeling out of sync with local time and disturbing their sleep.
Ideally, a person's sleep cycle follows the circadian clock, but sleep can be affected by numerous factors such as light, social timing (when others are awake, when work is required, etc.), naps, genetics, and more.
REM and non-REM sleep
While we sleep, the brain consumes far less power than during wakefulness, especially in non‑REM sleep. REM sleep, named for its rapid eye movements, also involves near‑total body paralysis and vivid dreaming. Non‑REM and REM represent two distinct sleep phases.
Typically, a night consists of 4‑6 cycles lasting roughly 90 minutes each, alternating between non‑REM and REM. Non‑REM starts and eventually deepens into slow‑wave or deep sleep, during which body temperature and heart rate drop, and the brain’s energy use declines while it replenishes ATP. Growth hormone is released in deep sleep, playing a key role in development.
REM makes up a smaller slice of total sleep time and is famous for hosting most dreams and nightmares. Lack of REM can trigger anxiety, irritability, hallucinations, and trouble focusing. Research shows that after REM deprivation the body tries to compensate, increasing both the frequency of REM periods and their overall duration – a phenomenon called REM rebound, underscoring REM’s importance. Though REM’s exact functions remain unclear, occasional REM loss may even yield short‑term benefits in some cases.
Sleep quality
We gauge sleep quality by how easy it is to fall asleep, stay asleep, and how many times we wake during the night. Subjectively, it’s also reflected in how refreshed we feel after waking.
Poor sleep quality disrupts the natural cycle and the shifts between stages. Good sleep requires a balance between the drive to sleep and the circadian rhythm. Ideally, melatonin peaks and core body temperature hits its low point after the mid‑point of the night but before you wake.
How much sleep do I need?
Sleep isn’t fully decoded, and the amount each person needs changes with factors like age and personal traits. When you get enough rest, daytime sleepiness and impairment should be absent.
Very generally, researchers have found that achieving 6-7 hours of sleep per night correlates with a number of positive health outcomes, but there are also many other factors that may affect these outcomes.
As we grow older, our total sleep time usually declines. Newborns, on the other hand, can sleep for many more hours than an adult. This gap closes during childhood, and around the age of five a child’s sleep requirement is roughly comparable to an adult’s.
Below are the CDCs recommendations for the number of hours a person should sleep based on age.
| Age Group | Recommended Hours of Sleep Per Day |
| 0–3 months | 14–17 hours |
| 4–12 months | 12–16 hours per 24 hours (including naps) |
| 1–2 years | 11–14 hours per 24 hours (including naps) |
| 3–5 years | 10–13 hours per 24 hours (including naps) |
| 6–12 years | 9–12 hours per 24 hours |
| 13–18 years | 8–10 hours per 24 hours |
| 18–60 years | 7 or more hours per night |
| 61–64 years | 7–9 hours |
| 65 years and older | 7–8 hours |