Sleep Calculator
Waking up in the middle of a sleep cycle can leave you groggy. This sleep calculator uses 90-minute cycles and about 14 minutes to fall asleep to suggest bedtimes for a wake-up time, or wake-up times for a bedtime. It runs in your browser.
Runs in your browser. Your files are never uploaded.
Loading Sleep Calculator…
How to use Sleep Calculator
- Choose I need to wake up at to get bedtimes, or I am going to bed at to get wake-up times.
- Set the time. For bedtime you can press Use current time to start from now.
- Read the list of suggested times, each with its number of sleep cycles and hours of sleep.
- Pick the time that suits you. Five or six cycles (7.5 to 9 hours) is a common target for adults.
How the calculator works
Sleep moves in repeating cycles of roughly 90 minutes. The idea is that waking at the end of a cycle, rather than in the middle of deep sleep, can feel easier. The tool counts back from your wake-up time by whole cycles and subtracts about 14 minutes for falling asleep, or counts forward from your bedtime in the same way.
Choosing an option
- Six cycles is 9 hours, five is 7.5 hours, four is 6 hours and three is 4.5 hours.
- Most adults should aim for the five or six cycle options when possible.
- Keep your bedtime and wake time steady, even at weekends.
- If you often lie awake for longer than 14 minutes, set the time a little earlier.
Why the times may not feel exact
Cycle length is an average. Stress, caffeine, alcohol, light, noise and age all change how long you take to fall asleep and how long each cycle lasts. Use the suggestions as a starting point and adjust to how you feel.
Limits
This tool gives estimates only and is not medical advice. It cannot detect sleep disorders. If you snore loudly, stop breathing in your sleep, or feel exhausted during the day, speak to a healthcare professional. Calculation happens in your browser and nothing is uploaded.
Why use this sleep calculator tool
- Two directions. Work backwards from the time you must wake up, or forwards from the time you are going to bed.
- Cycles and hours shown. Every option shows how many 90-minute cycles it contains and the total hours of sleep, for example 6 cycles = 9 h.
- Time to fall asleep included. The calculation adds about 14 minutes to drift off, so the times are for when you get into bed.
- Private and free. Everything is calculated in your browser. Nothing is uploaded, and there is no account or sign-up.
Frequently asked questions
What time should I go to bed if I wake up at 7 am?
Enter 7:00 in the wake-up mode. The calculator lists bedtimes that let you finish whole 90-minute cycles after about 14 minutes of falling asleep. Choosing five or six cycles gives roughly 7.5 to 9 hours of sleep.
How long is a sleep cycle?
A full cycle is commonly given as about 90 minutes, moving through lighter and deeper sleep and REM sleep. The real length varies between people and from night to night, so treat 90 minutes as an average, not a rule.
Why does the calculator add 14 minutes?
Most people do not fall asleep the moment they lie down. About 14 minutes is a typical figure used for falling asleep, so it is added to the bedtime or subtracted from the wake time. If you fall asleep faster or slower, adjust by hand.
How many hours of sleep do I need?
Many adults do well on 7 to 9 hours, while children and teenagers need more. Individual needs differ, so notice how rested you feel. Ask a doctor if you are always tired despite enough sleep.
Is my information sent anywhere?
No. The times are calculated in your browser and are never uploaded or stored on a server.
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