Sleep Calculator
Choose whether you know the time you want to wake up or the time you are going to bed. The calculator lists four times, for 3, 4, 5 and 6 full sleep cycles, so you can see how much sleep each one gives. You can set how many minutes you usually take to fall asleep, switch between a 12 hour and a 24 hour clock, and fill in the current time with one click. Everything runs in your browser.
A sleep cycle lasts about 90 minutes on average and moves through lighter and deeper stages, so waking at the end of a cycle can feel easier than waking in the middle of one. The times add your minutes to fall asleep, 15 by default, and then whole cycles. The 90 minutes is an average: real cycles vary from person to person and during the night, and many adults need around 7 hours or more of sleep. This is a planning aid, not medical advice, and it cannot diagnose a sleep problem. Talk to a health professional if you are always tired. The calculation runs in your browser.
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Student ToolsAbout the Sleep Calculator
During the night the body moves through repeating sleep cycles of lighter sleep, deeper sleep and dreaming sleep. A cycle lasts about 90 minutes on average, and the idea behind the calculator is that waking near the end of a cycle can feel easier than being woken in the middle of one. To find a bedtime, the tool subtracts whole cycles and the minutes you need to fall asleep from your wake-up time. To find wake-up times, it adds the minutes to fall asleep and then whole cycles to your bedtime. For example, to wake at 7:00 AM with 15 minutes to fall asleep, 6 cycles means going to bed at 9:45 PM for 9 hours of sleep, 5 cycles means 11:15 PM for 7.5 hours, and 4 cycles means 12:45 AM for 6 hours. The 90 minutes is only an average, since cycles vary between people and between nights, and the number of hours you need depends on your age and health. Many adults need 7 hours or more. The tool is a planning aid and does not diagnose sleep problems, so if you are tired all the time, speak to a doctor.
How long is a sleep cycle?▾
About 90 minutes on average, though it varies from person to person and from cycle to cycle. A full night usually has four to six of them.
What time should I go to bed to wake up at 7 AM?▾
With 15 minutes to fall asleep, 9:45 PM gives 6 cycles, 11:15 PM gives 5 cycles, 12:45 AM gives 4 cycles and 2:15 AM gives 3 cycles.
Does waking at the end of a cycle really help?▾
It is a popular idea and waking from lighter sleep is generally easier, but cycle lengths vary, so the times are a guide and not a guarantee.
How much sleep do I need?▾
It depends on your age and on you. Many adults need around 7 hours or more. The calculator shows the hours for each option so you can choose.
Is my data uploaded?▾
No. The calculation runs in your browser and nothing you enter is sent anywhere.