Sleep calculator
Waking at the end of a sleep cycle can feel easier than waking in the middle of deep sleep. Choose when you want to get up – or when you go to bed – to see times that fit whole cycles.
Runs in your browser: nothing you enter is sent anywhere.
How to use it
- Choose whether you know your wake-up time or your bedtime.
- Enter the time. If you are going to bed right now, tap the button to use the current time.
- Adjust the time to fall asleep or the cycle length if you know yours.
- Pick one of the suggested times; those that give at least 7 hours of sleep are marked.
How it works
Sleep runs in cycles of light sleep, deep sleep and REM sleep. Sleep researchers describe the first cycle as about 70–100 minutes and later ones as about 90–120 minutes (Carskadon and Dement, Principles and Practice of Sleep Medicine), so the calculator uses 90 minutes by default.
- bedtime = wake-up time − time to fall asleep − cycles × cycle length
- wake-up time = bedtime + time to fall asleep + cycles × cycle length
It shows 3 to 6 cycles (4.5 to 9 hours of sleep with 90-minute cycles).
Worked example
To get up at 7:00 AM with 15 minutes to fall asleep: 6 cycles (9 h) → go to bed at 9:45 PM; 5 cycles (7.5 h) → 11:15 PM; 4 cycles → 12:45 AM; 3 cycles → 2:15 AM.
Good to know
- Cycle timing is an approximation: no calculator knows your cycles exactly, and they change from night to night.
- A regular schedule, daylight in the morning and a dark, cool bedroom usually help more than exact timing.
- Children and teenagers need more sleep than adults.
Frequently asked questions
How long is a sleep cycle?
About 90 minutes on average, but it varies – roughly 70 to 120 minutes, and cycles later in the night tend to be longer. That is why the cycle length is editable.
How much sleep do adults need?
The American Academy of Sleep Medicine and the Sleep Research Society recommend 7 hours or more a night for adults (Watson et al., 2015). Five cycles of 90 minutes give 7.5 hours; times reaching 7 hours are marked.
Why add 15 minutes?
Most people need some time to fall asleep. The calculator assumes 15 minutes; change it if you usually fall asleep faster or slower.
Is it bad to wake up in the middle of a cycle?
Waking from deep sleep can leave you groggy for a while (sleep inertia). Timing by cycles is a rough way to avoid that – your own rhythm matters more than the exact minute.
What if I often cannot sleep or feel tired after a full night?
Ongoing insomnia, loud snoring, pauses in breathing or daytime sleepiness are worth discussing with a doctor; they can be signs of a treatable sleep disorder.