Sleep Calculator

Most adults do well on five or six full cycles a night, which is about seven and a half to nine hours. Four cycles (six hours) is on the short side but still lands you at the end of a cycle. Pick the option that fits the hours you have.

No. Ninety minutes is a widely used average. Real cycles vary from roughly 70 to 110 minutes between people and even across a single night — early cycles tend to be shorter and later ones longer. The tool uses 90 minutes as a practical estimate, not a measurement of your body.

That heavy, disoriented feeling is often sleep inertia — being woken out of deep sleep in the middle of a cycle. Waking near the lighter end of a cycle is what this tool tries to help with, though total sleep and sleep quality matter just as much.

It is the time most people take to drift off after the lights go out, called sleep latency. Counting cycles from the moment you get into bed would be too early, so the tool assumes you are actually asleep about 15 minutes later.

Then shift the suggested bedtime earlier by the extra time you need. If you usually lie awake for 40 minutes, going to bed about 25 minutes before the suggestion lines the cycles back up.

Partly. A single 90-minute cycle can leave you feeling refreshed because you wake from light sleep, and a very short 20-minute nap avoids deep sleep entirely. The awkward zone is roughly 40 to 60 minutes, when the alarm often catches you in deep sleep.

No. Children need more total sleep than adults, and teenagers naturally shift to a later body clock. The 90-minute cycle idea still applies, but use age-appropriate total sleep guidance rather than treating six adult cycles as a target.

Caffeine can delay sleep and reduce deep sleep for several hours after your last cup, so even a well-timed bedtime may not give you the rest the cycle count implies. Many people find it helps to stop caffeine six to eight hours before bed.

Yes. The calculation wraps around midnight, so a late bedtime correctly produces a morning wake-up time and an early wake target correctly produces an evening bedtime.

Sleep needs and cycle lengths are genuinely individual. Treat the output as a reasonable starting schedule, note how you feel on waking, and nudge the times until they fit. A consistent bed and wake time usually matters more than hitting an exact cycle.

No. This is a general timing aid, not a diagnosis or treatment. If you regularly struggle to fall asleep, wake unrefreshed, snore heavily or feel sleepy during the day, speak to a doctor or a sleep specialist.

No. The whole calculation happens in your browser. Nothing you enter is uploaded or stored on a server.