Sleep Duration Calculator
Plan your bedtime or wake-up time around natural sleep cycles so you wake up feeling fresh.
These health tools are still being tested and are updated regularly to give you a better experience. Results are estimates for information only — please confirm important results with a doctor. Read the medical disclaimer
Sleep Duration Calculator
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About the Sleep Duration Calculator
Waking up in the middle of a deep sleep cycle can leave you groggy. Timing your sleep to complete cycles can help.
How to use the Sleep Duration Calculator
- Enter your usual bedtime and wake-up time.
- Adjust how long it takes you to fall asleep (15 minutes by default) and choose your age group.
- Press Calculate to see your sleep duration and better bedtimes or wake-up times based on 90-minute cycles.
Formula explained
Wake-up time = bedtime + about 15 minutes to fall asleep + (number of cycles × 90 minutes)
Most adults need 5–6 cycles (7.5–9 hours). Recommended sleep: adults 7–9 hours · teenagers 8–10 hours · children 6–12 years 9–12 hours.
Worked example: Sleep Duration
Going to bed at 11:30 PM and waking at 6:00 AM, with 15 minutes to fall asleep, gives 6 h 15 min of sleep — less than the 7–9 hours recommended for adults. To wake at 6:00 AM after 5 full cycles, aim to be in bed by 10:15 PM.
Important limitations
- Estimates time asleep, not sleep quality.
- Sleep cycles vary between 80 and 110 minutes.
Frequently asked questions
How much sleep do adults need?
Most adults need 7–9 hours a night. Regularly sleeping less than 7 hours is linked to weight gain, high blood pressure and poor concentration.
Why do I feel tired after 8 hours of sleep?
Poor sleep quality, snoring or sleep apnoea, late screen use, anaemia, thyroid problems or low vitamin D can all cause tiredness.
What is a sleep cycle?
A sequence of light, deep and REM (dream) sleep lasting about 90 minutes. Waking at the end of a cycle, in light sleep, usually feels easier than waking from deep sleep.
Can I catch up on sleep at the weekend?
Sleeping in can reduce some sleepiness, but it does not fully reverse the effects of a week of short sleep and can disturb your body clock. A regular schedule every day is better.
Sources
- Watson NF et al. Recommended amount of sleep for a healthy adult (AASM/SRS). Sleep 2015;38:843-4.
- Paruthi S et al. Recommended amount of sleep for pediatric populations (AASM). J Clin Sleep Med 2016;12:785-6.
Medical disclaimer: These tools give general information and estimates only. They are not a diagnosis and do not replace advice from a qualified doctor. Always talk to your doctor about your results, and seek urgent medical help in an emergency. In an emergency call 112. Medical disclaimer · Terms of use · Privacy policy
