Sleep Calculator
Wake up at the end of a sleep cycle - not the middle - and feel genuinely rested.
I want to wake up at…
Find the best bedtimes
I am going to bed at…
Find the best alarm times
How It Works
Enter your time
Tell us when you want to wake up or when you plan to go to sleep.
We do the math
We count backwards (or forwards) in 90-minute sleep cycles, adding ~14 minutes to fall asleep.
Wake up refreshed
Waking at the end of a cycle means lighter sleep stages - far less groggy than mid-cycle alarms.
Why Sleep Cycles Matter
Visual: Typical 9-hour hypnogram
Deep sleep blocks are longest early in the night; REM blocks expand in later cycles.
Your brain doesn't sleep uniformly. Instead, it cycles through distinct stages - light sleep, deep slow-wave sleep, and REM - roughly every 90 minutes. Each complete cycle restores memory, mood, immunity, and physical tissue in ways that partial cycles simply cannot.
When an alarm pulls you out of deep or REM sleep mid-cycle, you experience sleep inertia - that heavy, disoriented grogginess that can persist for 30 minutes or more. Timing your alarm to the natural end of a cycle minimizes inertia because you're already in a lighter sleep stage.
This calculator adds a 14-minute fall-asleep buffer (the average sleep-onset latency for healthy adults) so the math starts from when you're actually asleep, not when your head hits the pillow.
This tool is for general informational purposes only and is not a substitute for medical advice. Consult a healthcare professional for sleep concerns.
Frequently Asked Questions
How many sleep cycles do I need per night?
Most adults need 5-6 complete cycles (7.5-9 hours) for full restoration. Fewer than 4 cycles consistently leads to cognitive impairment, mood issues, and weakened immunity.
What if I can't fall asleep in exactly 14 minutes?
The 14-minute average is a guideline. If you tend to fall asleep faster or slower, adjust your bedtime accordingly. The key insight - ending at a cycle boundary - remains the same.
Is this the same as the REM rebound method?
Not exactly. This calculator targets the light-sleep window at the natural end of any 90-minute ultradian cycle, not only REM. Every cycle end is a good wake point.
Can this help with shift work or irregular schedules?
Yes - just enter your actual planned sleep or wake time. The cycle math applies regardless of when you sleep, though consistent schedules align better with your circadian rhythm.
Why does the nap calculator recommend 90-minute naps?
A 90-minute nap completes one full cycle, including both slow-wave and REM phases, giving you memory consolidation and emotional processing benefits without the extended grogginess of waking mid-cycle.