Sleep Cycle Calculator

Compare clock times using an assumed 90-minute sleep cycle and a 14-minute time-to-sleep delay.

How to Use

Choose the calculation direction

Choose a target wake time to compare bedtimes, or a bedtime to compare wake times.

Enter the clock time

Use the local time you want to compare. The calculation wraps over midnight.

Read the assumptions

Every interval uses a 14-minute delay and a fixed 90-minute cycle. It does not measure your actual sleep.

A clock-time model, not a sleep-stage prediction

This calculator adds or subtracts a fixed 14-minute delay plus three to six assumed 90-minute cycles. Real cycles and time to fall asleep vary. The output cannot determine whether you will be in light or deep sleep when an alarm rings.

The displayed interval includes the assumed delay, so it is time allocated in bed rather than a measurement of time asleep. For a wake time of 07:00, six assumed cycles plus the delay give a bedtime of 21:46 the previous day.

CDC guidance says adults aged 18–60 generally need at least seven hours of sleep. A short option generated by this arithmetic is not a recommendation to restrict sleep. Sleep needs depend on age and circumstances.

Real-World Examples & Use Cases

Compare available time in bed

Compare several hypothetical bedtimes with a fixed wake time. The result is a planning estimate, not an individualized sleep-duration target.

How It Works

Allocated interval = 14 minutes + cycle count × 90 minutes Bedtime = target wake time − allocated interval Wake time = entered bedtime + allocated interval Clock times wrap over midnight. For 6 cycles: 14 + 6 × 90 = 554 minutes (9 hours 14 minutes). 07:00 − 9 hours 14 minutes = 21:46 the previous day.

Frequently Asked Questions

Can this tell me when I will be in light sleep?▼

No. A fixed cycle calculation does not measure or predict your actual sleep stages.

Does the duration show actual time asleep?▼

No. It includes an assumed 14-minute delay before sleeping. Your real time to fall asleep and time awake overnight can differ.

Is the shortest generated option recommended?▼

No. Generated times are arithmetic scenarios. Consider age-appropriate sleep guidance and speak with a healthcare provider if you regularly have trouble sleeping.

Limits and assumptions

Assumes 90-minute cycles and a 14-minute delay rather than measuring sleep.
Does not model sleep disorders, interrupted sleep, individual sleep-stage lengths, or daylight-saving clock changes.

References

CDC: About Sleep

Documentation updated on 2026-10-04. How we review tools

These results are estimates from simplified models, not a diagnosis or an individual treatment plan. Your circumstances can differ from the assumptions. Discuss medical decisions with a qualified clinician.

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