Sleep cycle calculator
Waking up in the middle of a sleep cycle leaves you tired. Use science to find the perfect moment to open your eyes.
Suggested Bedtimes:
* Includes 15 minutes to fall asleep.
Why you wake up tired
I genuinely hate that "hit by a truck" feeling in the morning. It usually happens because your alarm went off while you were in deep sleep. Humans sleep in **90-minute cycles**. If you wake up at the end of a cycle, you feel alert. If you wake up in the middle, you’re a zombie. This calculator works backward from your wake-up time to find the exact moments a cycle ends.
How many cycles do I need?
The average adult needs 5 to 6 cycles (7.5 to 9 hours) for optimal health. However, even 4 cycles (6 hours) can feel better than 5.5 cycles, because you're waking up at the right time.
What is the 90-minute rule?
The 90-minute rule is based on the average length of a human sleep cycle, which includes light sleep, deep sleep, and REM. Completing a full cycle prevents "sleep inertia"—that heavy, groggy feeling.
Does 15 minutes really matter?
Yes. It takes the average person about 14-16 minutes to actually fall asleep after closing their eyes. We factor this in so your cycles align with when you're actually unconscious.