Guides
Plain-English explanations for the science behind better sleep — what sleep cycles actually are, how many hours different people need, and how caffeine interacts with your body clock. Each guide links to the calculator that does the math.
Sleep science
How sleep cycles work
Light sleep, deep sleep, REM — what happens in each stage and why waking between cycles feels so different.
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Sleep needs
How much sleep do you need?
NSF ranges by age, what individual variation means, the signs of chronic sleep debt, and when to see a doctor.
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Caffeine
Caffeine and sleep
How caffeine's half-life works, a worked example of what's still in your system at bedtime, and how to find your personal cutoff.
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