Sleep science for humans
Know exactly when to rest.
18 free calculators for bedtime, wake time, sleep debt, chronotype, and more. Built on sleep science, not guesswork.
Sleep Cycle Calculator
Enter your wake time — we'll show you bedtimes that align with complete 90-minute cycles.
Go to bed at
Based on 90-minute cycles plus a 14-minute onset buffer.
All tools
Find the calculator for your question.
Explainers
Sleep science, in plain language.
Sleep Cycles Explained
What happens in each 90-minute cycle — and why waking mid-cycle feels terrible.
What Is a Chronotype?
Lion, Bear, Wolf, Dolphin — and the biology behind each one.
Caffeine and Sleep
That 2 pm coffee is still 50% active at 9 pm. The half-life is the enemy.
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Built on real sleep science.
Every calculator is built on peer-reviewed research: 90-minute sleep cycles, NSF age-based guidelines, caffeine half-life pharmacology, and circadian rhythm biology. The math is correct. The tools are free. No sign-up required. Learn about our methodology →