Common questions about sleep cycles, our tools, and your privacy.
Yes. All calculations happen in your browser using JavaScript. We do not have a database. We do not use cookies for tracking. We do not even have a server that processes your inputs. If you clear your browser data, your history disappears. That is the point.
The 90-minute cycle is an average. Individual cycles range from 80 to 120 minutes. Our calculator uses 90 minutes as a baseline and shows you a range of optimal bedtimes. For best results, track your own cycles for a week using our Sleep Debt Tracker.
Our tools can help you understand your sleep patterns, but they are not a treatment for insomnia. If you have chronic insomnia, please consult a sleep specialist or cognitive behavioral therapist for insomnia (CBT-I).
I built these tools for myself first. Then I figured other people might find them useful. The site is supported by advertising and affiliate links to products I actually use. No paywalls, no premium features, no data selling.
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The sweet spot is either 20 minutes or 90 minutes. Twenty minutes keeps you in light sleep, so you wake up without grogginess. Ninety minutes gives you one full cycle, including deep sleep and REM. Anything between 30 and 60 minutes usually causes sleep inertia — that heavy, disoriented feeling — because you wake up in the middle of deep sleep.
For one week, go to bed only when you actually feel sleepy — not when the clock says you should. Write down that time each night. By day four or five, you will see a pattern. Most people have a 45-minute window. Mine is 10:30 PM to 11:15 PM. If you want a faster estimate, use our Bedtime Finder tool.
Yes, but with adjustments. Children have shorter sleep cycles — about 60 to 75 minutes instead of 90. Our calculator defaults to 90 minutes, but you can change the cycle length in the settings. Teenagers usually need 9 to 10 hours, school-age kids need 10 to 11, and toddlers need 11 to 14. Always prioritize total sleep time over cycle perfection for kids.
Because hours are not the whole story. Sleep quality, fragmentation, and cycle alignment matter just as much. If you wake up five times a night, or if your alarm interrupts deep sleep, eight hours can feel like five. Take our Sleep Quality Score quiz to identify the specific problem. It is usually one of three things: inconsistent bedtime, too much caffeine after 2 PM, or a misaligned wake-up time.