Sleep Cycle Wake-Up Calculator
Sleep happens in 90-minute cycles. Waking at the end of a cycle means waking up naturally — no grogginess. Enter your target wake time and get the ideal bedtimes, or enter bedtime and get the best alarm times. Nothing uploaded.
Mode
I need to wake up at
Optimal Times
Nap Calculator (from now)
Learn more: sleep cycles and optimal bedtime
Why 7.5 hours can feel better than 8
Sleep moves through approximately 90-minute cycles of light sleep, deep sleep, and REM. Your alarm goes off at whatever time you set regardless of where in a cycle you are. Waking from deep sleep (Stage 3) causes sleep inertia - the heavy, disoriented feeling that can last hours. Waking from light sleep at the end of a cycle is immediately clear-headed. 7.5 hours is exactly 5 complete cycles. 8 hours wakes you 30 minutes into the 6th cycle - from deep sleep. The difference in how you feel is dramatic.
Optimal bedtime in three steps
First, choose mode: "I need to wake up at X" shows optimal bedtimes, or "I'm going to sleep at X" shows optimal alarm times. Second, set your fall-asleep latency - the default is 14 minutes, but you can adjust to your typical time to fall asleep (5-30 minutes). Third, read the optimal times - 4, 5, and 6 complete sleep cycles shown with moon icons indicating sleep quality, plus the nap calculator on the same page.
FAQ
Why do I feel worse after 8 hours of sleep than after 7.5?
Sleep progresses in 90-minute cycles. Waking in the middle of a deep sleep cycle causes sleep inertia - that heavy, groggy feeling. Waking at the end of a complete cycle feels much more refreshed even if total sleep time is slightly shorter. 7.5 hours is 5 complete cycles; 8 hours interrupts a cycle.
What is a good nap length?
A 20-minute nap targets the lighter Stage 2 sleep and avoids deep sleep entirely, giving an energy boost without grogginess. A full 90-minute nap completes one full cycle including REM sleep and provides deeper restoration. Anything in between (30-60 minutes) risks waking from deep sleep.
How long does it take to fall asleep?
The average adult takes approximately 14 minutes to fall asleep. The calculator adds this latency to your calculations. You can adjust it to match your own typical fall-asleep time (5-30 minutes) in the settings.