Quick Answer
How does a sleep calculator work?
// Answer
Sleep happens in cycles of about 90 minutes. Waking at the end of a cycle (rather than mid-cycle) leaves you feeling more refreshed. This calculator counts back (or forward) in 90-minute blocks from your chosen time, accounting for roughly 15 minutes to fall asleep, and suggests the best bed or wake times.
Why use this tool
Wake up less groggy
Ever woken up exhausted after 8 hours but refreshed after 6? Cycle timing is why. Aim for 5–6 complete cycles (7.5–9 hours). The highlighted "best" option gives you a full 5 or 6 cycles.
FAQ
Frequently asked questions
About 90 minutes, cycling through light, deep, and REM sleep.
Most adults feel best with 5-6 complete cycles, roughly 7.5 to 9 hours.
The average person takes about 14-15 minutes to drift off, so the calculator adds that buffer.
Yes, free and running in your browser.
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