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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.
SleepCycler8 hours of sleep, still exhausted? You're waking mid-cycle
James Hillleft a comment
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...
SleepCycler8 hours of sleep, still exhausted? You're waking mid-cycle