What is Sleep Calculator?
A Sleep Calculator determines the optimal times to go to sleep or wake up based on 90-minute sleep cycles. Waking up at the end of a complete sleep cycle helps you feel more refreshed and alert.
Sleep CalculatorFree Online Health Tool
Sleep Calculator is a free online health tool. Calculate optimal sleep and wake times based on 90-minute sleep cycles. Wake up feeling refreshed.
When to Sleep
Enter when you need to wake up
21:456 cycles • 9h
Recommended
23:155 cycles • 7.5h
Recommended
00:454 cycles • 6h
02:153 cycles • 4.5h
When to Wake Up
Enter when you're going to sleep
08:156 cycles • 9h
Recommended
06:455 cycles • 7.5h
Recommended
05:154 cycles • 6h
03:453 cycles • 4.5h
About Sleep Cycles:
A complete sleep cycle lasts about 90 minutes. Waking up at the end of a cycle helps you feel more refreshed. The calculator adds 15 minutes to fall asleep. Adults typically need 5-6 cycles (7.5-9 hours) per night.
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How to use & TipsSteps
- 1Enter your desired wake-up time to find optimal bedtimes
- 2OR enter your bedtime to find optimal wake-up times
- 3Choose times with 5-6 cycles (marked as Recommended) for best results
Use Cases
- -Plan bedtime based on when you need to wake up
- -Find the best wake-up time after a late night
- -Optimize sleep for shift workers
- -Improve morning alertness and reduce grogginess
- -Plan naps using 90-minute cycle timing
About Sleep Calculator
Everything you need to know about this tool and how to get the most out of it.
How Sleep Calculator Works
Sleep occurs in 90-minute cycles. The calculator adds 15 minutes to fall asleep, then calculates times that align with the end of complete cycles. 5-6 cycles (7.5-9 hours) is recommended for most adults.
Why Use Sleep Calculator?
Waking up mid-cycle causes 'sleep inertia' — that groggy feeling that can last hours. By timing your sleep to complete cycles, you wake up naturally at a lighter sleep stage, feeling more refreshed.
Tips & Best Practices
- 1Aim for 5-6 complete sleep cycles (7.5-9 hours) for optimal recovery
- 2Keep a consistent sleep schedule even on weekends to regulate your circadian rhythm
- 3Avoid screens 1 hour before bed — blue light suppresses melatonin production