# Sleep calculator: when to go to bed for the time you wake

Adults are advised to sleep 7 hours or more a night, and 7 to 9 hours suits most people. Sleep runs in cycles of roughly 90 minutes, so waking at the end of a cycle can feel easier. Enter your wake time and this calculator lists bedtimes for five and six cycles, allowing 15 minutes to fall asleep.

## How it works

### Cycles

A full cycle averages about 90 minutes but varies between 70 and 120. Treat the times as a guide, not an exact schedule.

### The target

Five cycles is 7.5 hours and six is 9 hours. Consistency of wake time matters more than any one night.

## Questions

### How much sleep do adults need?

Seven hours or more on a regular basis, according to the American Academy of Sleep Medicine and Sleep Research Society consensus.

### Is it bad to sleep more than 9 hours?

Occasionally it is normal, for example after illness or hard training. Regularly needing much more can be worth discussing with a clinician.

### When should I see someone about sleep?

Loud snoring with pauses in breathing, daytime sleepiness that affects driving or work, or insomnia lasting weeks are reasons to talk to a clinician.

## Sources

- [Watson NF et al. Recommended amount of sleep for a healthy adult. J Clin Sleep Med 2015](https://pubmed.ncbi.nlm.nih.gov/25979105/)

Accurate as of November 12, 2026.

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Canonical: https://revns.com/tools/sleep-calculator
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revns gives training guidance, not medical advice.