Circadian Rhythm Calculator
Find ideal bedtimes aligned with 90-minute sleep cycles and your target wake-up time for better circadian rhythm sleep.
What Is Circadian Rhythm?
Circadian rhythm is your internal 24-hour clock that regulates sleep, alertness, and hormone release. Aligning bedtime with natural sleep cycles can improve how rested you feel at wake-up. For more cycle-based timing, try the Sleep Cycle Calculator.
How Bedtimes Are Calculated
Enter your target wake time and how long you usually need to fall asleep. The calculator counts backward in 90-minute sleep cycles (adjustable) and lists bedtimes for 3 to 6 complete cycles.
Which Bedtime Should I Choose?
Five or six cycles (about 7.5 to 9 hours of sleep) are usually labeled as the best alignment. Shorter windows may work occasionally but are less ideal for long-term recovery.
Frequently Asked Questions
Why use 90-minute sleep cycles?
A full sleep cycle averages about 90 minutes. Waking between cycles can reduce grogginess compared with waking mid-cycle.
What if I fall asleep faster than 15 minutes?
Lower the time-to-fall-asleep value. The tool subtracts this latency before each suggested bedtime.
Does this replace medical sleep advice?
No. It is a timing helper. See a clinician if you have insomnia, sleep apnea, or persistent fatigue.
Can I change the cycle length?
Yes. Most adults use 90 minutes, but you can set 70 to 120 minutes if that matches your sleep pattern better.
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