SleepCycler
8 hours of sleep, still exhausted? You're waking mid-cycle
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James Hill

SleepCycler - 8 hours of sleep, still exhausted? You're waking mid-cycle

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Most sleep calculators just spit out times with no explanation. SleepCycler shows you exactly why each bedtime works — based on 90-minute sleep cycles, your age group, and a 15-minute fall-asleep buffer. Features: bidirectional calculator (wake time or bedtime), Sleep Now button, Sleep Debt Calculator with 7-night tracking and recovery plan, and a full sleep science blog. Free, no signup, no ads.

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James Hill
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I built this because I kept waking up exhausted after 8 hours of sleep and couldn't find a calculator that explained the actual science behind the recommendations. The core insight: it's not about total hours — it's about waking at the end of a 90-minute cycle rather than mid-cycle. A 7.5-hour night (5 cycles) will consistently feel better than 8 hours that ends mid-cycle. The Sleep Now button is my favorite feature — one tap uses your current time and instantly shows when to set your alarm tonight. No typing required. Happy to answer any questions about sleep science or how the calculator works.