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Sleep Calculator

Suggest bed or wake times from 90-minute sleep-cycle style planning — a schedule aid, not a medical sleep study.

Estimates only — not professional financial, medical, legal or engineering advice. Read full disclaimer.

Result

Fill in the form and click Calculate to see your result here.

How it's calculated

Candidate bed/wake clock times = target ± (cycles × ~90 min) ± latency, as implemented.

Example

Example: Sleep Calculator

Inputs

  • Wake Time: 06:30
  • Cycles: 5

Outputs

  • Suggested Bedtime: 22:45
  • Sleep Duration Hours: 7.5

This example uses typical sample values. Adjust the inputs above to see how the results change for your own numbers.

About this calculator

Falling asleep is not instant. This calculator works backwards (or forwards) from a wake time using typical ~90-minute cycle blocks plus a short fall-asleep buffer so you do not set an alarm in the middle of a cycle on purpose.

Insomnia, apnea, and shift work need clinicians. Caffeine after 4 pm in Kathmandu café culture will beat any bedtime the page suggests.

Frequently Asked Questions

It assumes 90-minute sleep cycles plus a 15-minute fall-asleep buffer, then counts backward from your wake time: bedtime = wake − (cycles × 90) − 15 minutes, wrapping past midnight. Default 5 cycles (~7.5 h sleep + 15 min).
Average adult NREM–REM cycles are often ~90 minutes but vary by person and night (sleep science). This is a planning heuristic, not polysomnography.
Common “about 7.5 hours” target. 4–6 cycles spans roughly 6–9 hours of sleep time excluding the buffer. Adults’ needs differ (often ~7–9 h in public-health messaging).
Fixed in code for sleep-onset. Insomnia or delayed onset needs a larger personal buffer — re-run earlier.
Not modelled. This is overnight cycles to a wake clock.
Not included. Chronotype and caffeine are outside the arithmetic.
You can enter any wake HH:MM. Quality of day-sleep is another issue.
Not diagnostic. See a clinician for OSA, narcolepsy, etc.
Schema 1–8. 8 × 90 min = 12 h sleep time plus buffer — usually too long unless recovering.
People often feel groggier after N3; this tool only aligns clock times to multiples of 90. It cannot see your stages.

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