Sleep Calculator

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Find the best times to fall asleep or wake up based on 90-minute sleep cycles, so you wake between cycles feeling refreshed rather than groggy.

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Based on 90-minute sleep cycles. 5 to 6 cycles (about 7.5 to 9 hours) suit most adults; waking between cycles helps you feel rested.

About Sleep Calculator

The sleep calculator suggests when to go to bed for a given wake-up time, or when to wake up if you are going to bed now. Its recommendations are built on 90-minute sleep cycles: waking between cycles, rather than mid-cycle, is what leaves you feeling rested instead of groggy.

Tell it your target time and how long you typically take to fall asleep (15 minutes by default), and it lists options from one to six full cycles, flagging five and six cycles — about 7.5 to 9 hours of sleep — as the recommended choices for most adults.

It is a simple, free way to stop guessing bedtime math: the tool counts backwards or forwards, including your falling-asleep buffer, and highlights the best matches.

How to use Sleep Calculator

  1. Choose your plan: “I want to wake up at” or “I'm going to bed at”.
  2. Set the wake-up time or bedtime accordingly.
  3. Adjust the time you usually need to fall asleep (the default is 15 minutes).
  4. Pick one of the suggested times — options with 5 or 6 full cycles are marked as recommended.

Frequently asked questions

A full cycle moves through light sleep, deep sleep and REM in roughly 90 minutes on average. The calculator schedules whole cycles so your alarm lands near a cycle boundary, when waking feels easiest.

Five to six cycles — about 7.5 to 9 hours — suit most adults, and the tool flags those options as recommended. Fewer cycles can work occasionally but are not a sustainable pattern.

The calculator shifts every suggestion by that buffer, since cycles only start once you are actually asleep. If you typically drift off in 30 minutes rather than 15, update the field for accurate bedtimes.

Alarms that fire during deep sleep tend to produce sleep inertia — that heavy, disoriented feeling. Timing your wake-up near the end of a cycle, as this tool does, usually makes mornings gentler.

No — cycle length varies between people and across the night, so results are estimates based on a 90-minute average, not medical advice. Persistent sleep problems are worth discussing with a doctor.
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