🌙 SomniCalc

Sleep Cycle Calculator

Wake up refreshed by timing your sleep to natural 90-minute REM cycles.

Includes ~15 min fall-asleep buffer. Bedtimes shown below.

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❓ How Does This Work?

Sleep cycles last approximately 90 minutes, each ending with a period of lighter sleep — the ideal moment to wake up. Most adults need 5–6 complete cycles (7.5–9 hours).

This calculator adds a 15-minute fall-asleep buffer and then counts backward (or forward) in 90-minute increments to give you the perfect bedtime or alarm time.

Waking at the end of a cycle instead of the middle dramatically reduces sleep inertia — the grogginess that hits when your alarm catches you in deep sleep.

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Frequently Asked Questions

What time should I go to sleep?

The best bedtime depends on when you need to wake up. Our sleep calculator works backwards from your wake time in 90-minute cycle increments to show you optimal bedtimes that avoid waking mid-cycle.

How long is a sleep cycle?

A complete sleep cycle lasts approximately 90 minutes and includes light sleep, deep sleep, and REM sleep stages. Most adults need 4-6 complete cycles per night (6-9 hours).

Why do I feel groggy even after 8 hours of sleep?

You likely woke up in the middle of a sleep cycle. Waking during deep sleep causes sleep inertia — that groggy, disoriented feeling. Our calculator helps you time your alarm to the end of a cycle.

How many sleep cycles do I need?

Most adults feel best with 5-6 complete sleep cycles (7.5-9 hours). Athletes and growing teenagers may need more. 4 cycles (6 hours) is the minimum for most people to function well.

What is REM sleep?

REM (Rapid Eye Movement) sleep is the stage where most dreaming occurs. It plays a critical role in memory consolidation, emotional processing, and cognitive function. It typically occurs in the later cycles of the night.

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