SleepCycleCalcFrequently Asked Questions
How the calculators work, how much to trust them, and the sleep questions people actually ask.
Frequently asked questions
Is SleepCycleCalc free?
Yes. Every calculator on this site — sleep cycle, bedtime, wake-up, nap and sleep debt — is free to use with no sign-up and no limits. A Pro tier is planned at $9/month, but it is not available yet and nothing is billed.
Does SleepCycleCalc store my sleep data?
No. All calculations run locally in your browser. The times you enter are never sent to or stored on a server — there is nothing to sign up for and nothing to sync.
Is a sleep cycle calculator medical advice?
No. It is a planning tool built on the average 90-minute sleep cycle. Persistent poor sleep, loud snoring, breathing pauses, or heavy daytime sleepiness deserve a proper medical evaluation, not a web calculator.
How accurate are the times it gives?
The arithmetic is exact; the biology is approximate. Real sleep cycles average around 90 minutes but range roughly 80–110 minutes per person and per night, so treat the outputs as a good window to aim at and adjust based on how you feel over a week or two of consistent timing.
What is the fall-asleep buffer?
The minutes between getting into bed and actually being asleep. Cycles run from sleep onset, so the calculator adds this buffer (15 minutes by default, adjustable on every tool) before counting cycles.
Can I use it for shift work or naps?
Yes — the maths does not care what the clock says. The nap calculator covers planned daytime sleep, and the 'sleep now' tool is handy for irregular schedules. Shift workers with persistent sleep problems should look into shift work sleep disorder with a clinician.
Why 90 minutes and not 60 or 120?
Because that is what the average full pass through N1, N2, N3 and REM sleep measures in adults. It is the standard figure used in sleep education — a useful average, with the honest caveat that your own cycles may run shorter or longer.