Sleep Duration Calculator
Best bedtime or wake-up time using 90-minute cycles. Free, private and instant.
How to use the Sleep Calculator
- Choose I want to: Wake up at a set time (find bedtime) or Go to bed at a set time (find wake-up time).
- Enter age.
- Answer any extra questions that appear for your choices.
- Press Calculate to get an instant result with a colour scale, chart and plain-English explanation.
About the Sleep Calculator
The sleep duration calculator suggests bedtimes or wake-up times that line up with 90-minute sleep cycles, adds about 15 minutes to fall asleep, and checks the result against the recommended hours for your age.
Also known as: sleep calculator, bedtime calculator, wake up time calculator, sleep cycle calculator, when should I go to bed.
Formula and cut-offs
Bedtime = wake time - (cycles x 90 min) - 15 min. Wake time = bedtime + 15 min + cycles x 90 min. Recommended: adults 7-9 h, teens 8-10 h, school age 9-11 h, over 65 7-8 h.
Frequently asked questions
How many hours of sleep do I need?
Most adults need 7 to 9 hours, teens 8 to 10 and school-age children 9 to 11.
What is a sleep cycle?
A cycle of light, deep and REM sleep lasts about 90 minutes and repeats 4 to 6 times a night.
Does waking at the end of a cycle help?
Many people feel less groggy, but total sleep time matters most.
Sources and references
- CDC - About sleep
- Hirshkowitz M et al. National Sleep Foundation's sleep time duration recommendations. Sleep Health, 2015
Written and checked by the MediHub editorial team against the sources above. Read how we build and review our calculators.
More health calculators
- Walking Calories Calculator
- One-Rep Max Calculator
- Ovulation Calculator
- Menstrual Calendar
- Pregnancy Risk Information Tool
- Menopause Age / Stage Information Tool
- More Sleep & recovery calculators
- All health calculators
- Compare medicine prices in 32 countries
Last updated . This calculator is for education only and is not medical advice. See the medical disclaimer.