Sleep Calculator
Enter the time you need to wake up to see when to go to bed, or enter your bedtime to see when to set the alarm. Times are worked out from sleep cycles of about 90 minutes, plus the time it takes you to fall asleep.
Free, no sign-up. What you enter stays in your browser: it is not saved or sent to HerFound. Reviewed .
What do you want to work out?
Most people take 10 to 20 minutes. Leave it at 15 if you are not sure.
Go to bed at about
11:15 pm
That gives 5 sleep cycles, or 7 hours 30 minutes of sleep.
- 6 cycles, 9 hours of sleep
- 9:45 pm
- 5 cycles, 7 hours 30 minutes of sleep
- 11:15 pm
- 4 cycles, 6 hours of sleep (less than adults need)
- 12:45 am
These times use an average cycle of 90 minutes, and your own cycles will differ. Adults are advised to get 7 or more hours of sleep a night. If you often cannot sleep, or you are very tired in the day, talk to a doctor.
This is general information, not medical advice. It cannot take your own health history into account. For anything that worries you, speak to a doctor, midwife or pharmacist.
How it works
Sleep runs in cycles. In each cycle you pass through light sleep, deep sleep and REM (dream) sleep, and you may wake briefly between cycles. Waking near the end of a cycle often feels easier than waking in the middle of deep sleep.
The calculator uses the common average of 90 minutes for one cycle. Bedtime = wake-up time minus (number of cycles × 90 minutes) minus the minutes you need to fall asleep. Wake-up time = bedtime plus the minutes to fall asleep plus (number of cycles × 90 minutes).
It shows 4, 5 and 6 cycles, which is 6 hours, 7 hours 30 minutes and 9 hours of sleep. The time to fall asleep is set to 15 minutes, a typical figure, and you can change it to anything from 0 to 60 minutes.
What it cannot tell you
- 90 minutes is an average, not your own cycle. The US National Heart, Lung, and Blood Institute describes cycles of about 80 to 100 minutes, single cycles can be shorter or longer than that, and they change through the night. The times are a starting point, not a precise alarm.
- The total amount of sleep matters more than cycle timing. Adults are advised to sleep 7 or more hours a night, so 4 cycles (6 hours) is too little for most adults as a regular habit.
- It cannot tell you how well you sleep or why you feel tired. If you often have trouble falling asleep or staying asleep, or you are very sleepy in the day for more than a few weeks, talk to a doctor.
Apps that do this for you
A calculator answers once. These apps keep track over time. Compare all self-care and mood apps.
ALO Wellness Club
A yoga and fitness class app: on-demand yoga, Pilates, strength and meditation, formerly Alo Moves
Bearable
A symptom and mood tracker: log your health factors and see how they shape how you feel.
Calm
A meditation and sleep app: Sleep Stories, guided meditations and breathing exercises to help you unwind.
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Common questions
To wake up at 7:00 am, go to bed at about 11:15 pm for 5 sleep cycles (7 hours 30 minutes of sleep) or 9:45 pm for 6 cycles (9 hours). These bedtimes allow 15 minutes to fall asleep and use sleep cycles of 90 minutes.
A sleep cycle lasts about 90 minutes on average. The US National Heart, Lung, and Blood Institute says the cycle starts over every 80 to 100 minutes and most people have four to six cycles a night. Cycle length differs between people and from one cycle to the next.
Adults need 7 or more hours of sleep a night on a regular basis. This is the joint recommendation of the American Academy of Sleep Medicine and the Sleep Research Society. Many adults feel best with 7 to 9 hours.
Waking up at the end of a sleep cycle often feels easier, because you are in lighter sleep. Waking from deep sleep can leave you groggy for a while. A calculator can only estimate where your cycles end, so getting enough total sleep is still the more important goal.
Falling asleep takes most healthy adults about 10 to 20 minutes. This sleep calculator uses 15 minutes by default and lets you change it. If it often takes you much longer than 30 minutes to fall asleep, mention it to a doctor.