Sleep Calculator

Our free sleep calculator uses the science of 90-minute sleep cycles to help you find the best time to go to bed or wake up. Most adults cycle through light sleep, deep sleep, and REM sleep roughly every 90 minutes. Waking at the end of a complete cycle — rather than mid-cycle — can help you feel more alert and less groggy.

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About sleep cycles

A typical sleep cycle lasts about 90 minutes and includes light sleep, deep sleep, and REM sleep. Most adults need 4-6 complete cycles (6-9 hours) per night. This calculator adds 15 minutes to fall asleep. Individual sleep needs vary. This tool is for informational purposes only.

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Frequently Asked Questions

How does the sleep calculator work?

The calculator uses 90-minute sleep cycles to suggest optimal bedtimes or wake times. It also adds 15 minutes for the average time it takes to fall asleep. By waking at the end of a cycle you avoid interrupting deep sleep, which can cause grogginess.

How many sleep cycles do I need per night?

Most adults need 4 to 6 complete sleep cycles, which is roughly 6 to 9 hours. Five cycles (7.5 hours) is the most common recommendation for healthy adults.

Is 6 hours of sleep enough?

Six hours equals four 90-minute cycles, which is on the low end. While some people function adequately on 6 hours, most sleep research suggests 7-9 hours for optimal health, mood, and cognitive performance.

What is the best time to go to bed?

The best bedtime depends on when you need to wake up. Use the calculator to work backwards from your alarm time. For a 7 AM wake-up, ideal bedtimes are around 9:45 PM, 11:15 PM, or 12:45 AM.

Can naps replace lost night-time sleep?

Short naps (20-30 minutes) can temporarily boost alertness, but they do not fully replace deep sleep and REM sleep that occur during longer overnight sleep periods.

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