Sleep Cycle Optimizer
Find the ideal bedtime or wake-up time based on 90-minute sleep cycles. Includes NASA-standard Power Nap analysis and science-backed sleep stage explanations.
How to use
- 1Select mode: "I want to wake up at..." or "I'm going to sleep now"
- 2Enter your target wake-up time or tap "Right Now"
- 3View ideal sleep times based on 90-minute cycles
- 4Choose an "Excellent" slot (5-6 cycles) for optimal rest
Frequently Asked Questions — Sleep Cycle Optimizer
How many hours of sleep do I need?+
Adults need 7-9 hours per night, which equals 5-6 complete 90-minute sleep cycles. More important than the total hours is waking at the END of a cycle. Waking after 7.5h can feel better than 8h if 8h lands mid-cycle, causing sleep inertia.
Why do I still feel tired after 8 hours of sleep?+
You're likely waking mid-cycle during Deep Sleep or early REM — known as sleep inertia. This causes grogginess that can last 30-60 minutes. Fix: align sleep and wake times to multiples of 90 minutes using this calculator.
What is the best power nap duration?+
20 minutes (Energy Nap): The gold standard — boosts alertness without sleep inertia. Recommended by NASA and the US military. 45 minutes risks waking mid-deep-sleep. 90 minutes completes a full cycle, ideal for serious sleep debt recovery.
What are the stages of a sleep cycle?+
Each 90-minute cycle includes: Light Sleep (N1+N2, ~50%) → Deep Sleep/Slow Wave (N3, ~20%) → REM Sleep (~30%). REM is when your brain consolidates memories and emotions. Waking at the end of REM leaves you feeling refreshed and mentally sharp.