Sleep Calculator
Sleep runs in ~90-minute cycles. Wake at the end of a cycle and you feel rested; wake mid-cycle and you feel wrecked — even after more hours. Time it right.
What time do you need to wake up?
Why 90 minutes?
A full sleep cycle — light → deep → REM — runs about 90 minutes. Across a night you want 5 or 6 complete cycles (7.5–9 hours). The trick isn't just total hours; it's waking between cycles rather than in the middle of deep sleep. This adds ~15 minutes to fall asleep, then counts back (or forward) in 90-minute blocks so your alarm lands on a natural surfacing point. Aim for the highlighted 5–6 cycle options.