Sleep Calculator
Find the best time to wake up or go to sleep based on sleep cycles.
To wake up feeling refreshed at 07:00 AM, you should try to fall asleep at one of these times:
How to use
- 1
Pick whether you want to set a wake-up time or a bedtime
- 2
Enter the time using the time picker
- 3
Choose one of the recommended times based on 90-minute sleep cycles
Sleep Calculator — Find the Best Bedtime & Wake Time
Free sleep cycle calculator that recommends the best times to fall asleep or wake up based on 90-minute REM cycles.
Skycally's Sleep Calculator helps you wake up feeling refreshed instead of groggy. Sleep happens in roughly 90-minute cycles, and waking at the end of a cycle leaves you feeling far more rested than waking in the middle of deep sleep. Just enter the time you need to wake up — or the time you plan to head to bed — and the tool will instantly suggest the best times to do the other.
We add a 14-minute buffer for the average time it takes to fall asleep, then walk forward or backward in 90-minute steps. The result is a list of times that align with the natural end of a sleep cycle. Aim for 5 to 6 full cycles (about 7.5 to 9 hours) for the best results, though 4 cycles can work in a pinch.
Everything runs in your browser — no signup, no data collected. Use it nightly to dial in a consistent schedule, plan around early flights, or help kids and shift workers get the most out of every hour of rest.
Frequently Asked Questions
How does the sleep cycle calculation work?
Each sleep cycle lasts about 90 minutes. We add a 14-minute fall-asleep buffer to your input and then count complete cycles forward or backward to suggest times that align with the end of a cycle.
How many cycles should I aim for?
Most adults feel best with 5–6 cycles (7.5–9 hours). 4 cycles (6 hours) can work occasionally but isn't ideal long term.
Why do I feel groggy even after 8 hours?
You may have woken up in the middle of a deep sleep stage. Aligning your wake time to the end of a cycle usually helps reduce sleep inertia.
Is the 90-minute cycle exact for everyone?
No — cycles vary from 80 to 110 minutes between people. The 90-minute average is a useful approximation that works well for most adults.
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