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Sleep cycle calculator

Pick a wake-up or bedtime to see the cycle-aligned suggestions.

How Sleep cycle calculator works

Sleep Cycle Calculator suggests bedtimes or wake-up times based on the 90-minute sleep cycle model. You either enter a time you want to wake up (and receive suggested bedtimes) or enter a time you plan to go to sleep (and receive suggested wake-up times). The calculations all run in the browser; nothing you type is sent anywhere, and the tool is available offline once loaded.

Be honest about the limits of this approach. The 90-minute cycle is an approximation derived from sleep research averages. Individual sleep cycles range from roughly 70 to 120 minutes and shift in length across the night. The first cycles of the night include more deep sleep; later cycles include more REM. Waking at the end of a cycle (when sleep is lightest) tends to feel less groggy for many people, but this varies considerably by individual. The tool also adds approximately 15 minutes for falling asleep, which is also an average.

Written by Bastien Sulyan

How to use Sleep cycle calculator, step by step

  1. Choose whether you want to calculate a bedtime or a wake-up time.
  2. Enter your target wake-up time (or your planned bedtime).
  3. Review the list of suggested times, each representing a different number of complete 90-minute cycles.
  4. Choose the suggestion that fits your schedule and allows at least 5 or 6 complete cycles (7.5 to 9 hours) for a full night.

Common use cases

  • You need to be at work by 07:30 and want to know what time to go to bed to avoid waking mid-cycle.
  • You are taking a short nap and want to time it at exactly one or two sleep cycles to avoid sleep inertia.
  • A shift worker who finishes at 06:00 wants to plan their daytime sleep schedule around natural cycle boundaries.
  • A student revising late wants to calculate the latest bedtime that still allows 4 complete cycles before an early exam.

Frequently asked questions

Is 90 minutes the exact length of a sleep cycle?

No. Sleep research uses 90 minutes as a widely-cited average, but individual cycles vary from roughly 70 to 120 minutes and change over the course of a night. This tool uses 90 minutes as a practical approximation; the suggested times are starting points to experiment with, not precise guarantees.

Why does the tool add 15 minutes for falling asleep?

The 15-minute offset accounts for typical sleep latency: the time between lying down and actually falling asleep. This is an average drawn from sleep research. People with insomnia or anxiety may take much longer; those who are very tired may fall asleep faster.

How many sleep cycles should a full night contain?

Most adults complete 5 to 6 cycles per night, which is 7.5 to 9 hours of sleep. Fewer than 5 cycles (less than 7.5 hours) may leave you short on REM sleep, which accumulates in later cycles and is important for memory consolidation and mood regulation.

Do the times I enter get saved or sent anywhere?

No. The bedtime and wake-up inputs you type are used only for the arithmetic in your browser tab. They are not transmitted, stored in a database, or tracked in any way.

Can I use this to time a power nap?

Yes. A single sleep cycle (90 minutes) is one option for a longer nap. For a true power nap targeting light sleep only, 20 to 25 minutes before entering deep sleep is commonly recommended. The calculator shows a 90-minute option; shorter nap durations would need to be timed by a standard alarm.

Does this tool give medical sleep advice?

No. The calculator applies a general sleep cycle model to arithmetic. It is not a diagnostic tool and does not account for sleep disorders, individual physiology or age-based sleep requirements. For sleep difficulties, consult a healthcare professional.