Calculadora de Hora de Dormir
- Created by
- Renato Passos, Eng. de Software
- Reviewed by
- Renato Passos, Eng. de Software
Last updated: Apr 18, 2026
Formula
hora_dormir = hora_acordar − ciclos·90min − 15min (adormecer)
About this calculator
The Sleep Time Calculator helps you determine the best time to go to bed based on your desired wake-up time. Sleep is structured in cycles of approximately 90 minutes, and waking up in the middle of a cycle can leave you groggy and tired. This tool calculates bedtimes that align waking up with the end of a cycle, maximizing restfulness.
How it works: you enter the time you need to wake up and how many hours of sleep you want (or let the calculator suggest standard cycles). The formula considers that each cycle lasts 90 minutes and that it takes about 15 minutes to fall asleep. Thus, we subtract multiples of 1.5 hours (cycles) plus 15 minutes from the wake-up time to get the ideal bedtime.
Use this calculator when planning your sleep routine, especially before important days like exams, interviews, or trips. It is useful for adjusting bedtimes for children, elderly, or anyone wanting to improve sleep quality. Try it if you suffer from mild insomnia or have irregular schedules.
Important cautions: each person's sleep cycle is slightly different (between 70 and 110 minutes). The calculator uses 90 minutes as an average. Also, the time to fall asleep may vary; if you take longer than 15 minutes, adjust manually. It does not replace medical advice for sleep disorders.
Frequently asked questions
Why does waking up in the middle of a cycle make you feel tired?
Because sleep has stages: light, deep, and REM. Waking during deep or REM sleep causes sleep inertia, that groggy and confused feeling.
Can I use the calculator if I have insomnia?
Yes, but it does not replace treatment. It helps regulate schedules, but if insomnia persists, see a doctor.
What if the calculated bedtime is too early or too late?
Adjust the number of cycles: sleep 5 or 6 cycles instead of 4. The ideal is between 4 and 6 cycles (6 to 9 hours of sleep).
Does the calculator work for babies or children?
Yes, but remember that babies have shorter cycles (about 50-60 min). For children, use with adaptation.
Do I really need to add 15 minutes to fall asleep?
It's an average. If you take longer, add that extra time. The important thing is to adjust to your reality.