Sleep Cycle Calculator
Find the best time to sleep or wake up based on 90-minute sleep cycles. Waking between cycles helps you feel more rested. Allows 14 minutes to fall asleep. Everything in your browser.
Considera 14 minutos para pegar no sono. Cada ciclo de sono dura cerca de 90 minutos. Acordar entre ciclos faz você se sentir mais descansado.
Como funciona
Durante a noite o sono passa por ciclos de aproximadamente 90 minutos, alternando entre sono leve, profundo e REM. Se o despertador toca no meio de um ciclo, sobretudo durante o sono profundo, você acorda grogue. Quando o alarme pega o fim de um ciclo, a sensação é bem mais natural.
Um adulto saudável geralmente fecha 4 a 6 ciclos completos por noite, o que dá algo entre 6 e 9 horas. A calculadora acrescenta 14 minutos para você pegar no sono e devolve horários que caem no final de um ciclo. O cálculo roda todo no navegador e nada vai para servidores.
Sleep cycles of ~90 minutes
Human sleep runs in cycles of roughly 90 minutes. Each one moves through three NREM stages (N1 drowsy onset, N2 light sleep, N3 deep slow-wave sleep) before reaching a REM period, where most dreaming happens. Wake up at the tail end of a cycle, when sleep is shallow, and you feel far less of the grogginess known as sleep inertia than if the alarm pulls you out of N3. That is what apps like Sleep Cycle and smart alarms are trying to do. The calculator works backwards with bedtime = wake − (cycles · 90 min) − sleep latency, where sleep latency is taken as about 14 minutes. Example: to wake at 6:00 with 5 complete cycles (7h30m of sleep), go to bed at 22:06; with 4 cycles (6h00m), 23:36.
Clinical context and age
The American Academy of Sleep Medicine recommends 7–9 hours (5–6 cycles) for healthy adults, 8–10 hours for adolescents, and 7–8 hours for adults over 65, who tend to have slightly shorter cycles and lighter sleep. Sleep too little for too long and the deficit builds into a sleep debt that drags down memory, immunity and metabolic regulation. Treat the 90-minute figure as a ballpark. People vary anywhere from 80 to 120 minutes, the early cycles of the night carry more N3, and the later ones lean toward REM. Brazil's ANVISA approved melatonin as a food supplement under RDC 922/2024; if you use it, take it about 30–60 minutes before the planned bedtime.
FAQ
Are 6 hours enough if I time the cycles? Four cycles is the bare minimum for the odd night. Sleeping under 7h as a habit still raises cardiovascular and cognitive risk, no matter how well you line up the cycles.
Why do I sometimes wake before the alarm and feel fine? You most likely finished a cycle on your own. Internal cues such as core temperature and cortisol nudge the body toward lighter sleep as morning approaches.
Does the 90-minute figure apply to naps? It does. A 90-minute nap usually fits one full cycle and leaves you with less sleep inertia, whereas a 60-minute nap can end in deep sleep. Quick naps of 10–20 minutes work too, since they never leave N1/N2.
What if my schedule shifts every day? When it comes to poor sleep quality, an erratic schedule predicts more trouble than short total duration. Aim to hold a fixed wake time, weekends included.
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The best time to sleep or wake up
Waking up groggy even after hours in bed has an explanation. Sleep arranges itself in cycles of about 90 minutes, and waking in the middle of one is what leaves you worn out. This calculator points out the best times to sleep or wake, slotted to the end of each cycle.
Tell it the time you need to wake and it shows when to lie down. Or say when you'll sleep and find the best moments for the alarm. The calculation also includes the 14 minutes we take on average to drift off, which makes the estimate more realistic than a bare number.
Tuning the time to your sleep's natural rhythm is a simple way to wake up more rested. Everything runs in the browser, and nothing is stored.