Sleep Duration Calculator
＋More features: one-week sleep log, working back to your bedtime
Was this week enough? (sleep-debt check)
Each time you enter a day’s sleep (in hours, decimals OK), the average and the difference from 7 hours a day are calculated from just the days entered so far (blank days are ignored).
Work back to when you should go to bed
Enter your target sleep duration, and the bedtime is worked back from the wake-up time in the form above.
Just enter when you went to bed and when you got up to instantly see how long you slept — calculated correctly even across midnight. Useful for getting your sleep rhythm in order.
How to use
- Enter your bedtime (the time you fall asleep).
- As soon as you enter your wake-up time, the sleep duration appears right below. No button needed.
- “Up at 6 and want 7 hours of sleep” — you can also use it to try out bedtimes worked back from your wake-up time.
How it is calculated
- Sleep duration = wake-up time − bedtime (24-hour clock; if the wake-up time is earlier, it is treated as crossing midnight)
- Example: bed at 23:00 → up at 6:30 = 7 hours 30 minutes
Sources and assumptions
- This is simple arithmetic on clock times. Sleep needs vary from person to person, and this tool does not judge “how many hours are appropriate”.
Assumptions and notes
- Naps are not included. If you want to include naps, calculate them separately and add them up.
- Sleep quality (depth, night-time awakenings) cannot be measured. If strong daytime sleepiness persists, consult a medical professional.
Frequently asked questions
How many hours of sleep are ideal?
Sleep needs vary greatly with age and between individuals, and there is no single right answer. A practical yardstick is whether you can get through the day without strong sleepiness.
I heard waking up at a multiple of 90 minutes is better?
The sleep cycle is often said to be “about 90 minutes”, but the actual cycle varies between people (and even within one night), so this tool does not make 90-minute recommendations.
How should I handle going back to sleep or hitting snooze?
Use the time you finally got out of bed as the wake-up time to get your “time lying down”, or the time you first woke up to get your “main sleep”. Choose whichever matches your purpose.