Recovery
As of 2026-04-24
How Sleep Calculator works
Methodology for the Sleep Calculator: formulas, coefficients, data sources, assumptions, and known limitations.
Scope
Suggests bed and wake times that align with 90-minute sleep cycles.
Formula
bedtimes = wake_time - n * 90 min - 14 min sleep latency, for n = 5, 6 cycles (7.5h, 9h).
Coefficients
| Parameter | Value | Note |
|---|---|---|
| Cycle length | ~90 minutes | |
| Typical sleep latency | ~14 minutes | |
| Target cycles (adult) | 5–6 cycles |
Data sources
- Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation's sleep time duration recommendations: methodology and results summary. Sleep Health. 2015;1(1):40-43. — PMID 29073412. Source of the 7-9 h adult target.
- Consensus Conference Panel; Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus statement of the American Academy of Sleep Medicine and Sleep Research Society. Sleep. 2015;38(6):843-844. — PMID 26039963. AASM/SRS companion consensus to the NSF duration recommendations.
- Centers for Disease Control and Prevention — How Much Sleep Do I Need? — CDC public-health summary consistent with the NSF and AASM recommendations.
Assumptions
- Ninety-minute cycle length is a population average; individuals vary.
Approximation range
Actual cycle length varies 80–120 minutes between people and across the night.
Limitations
- Cannot see shift work, caffeine timing, or sleep disorders.
- Does not replace a sleep-medicine consultation for insomnia or OSA.
Reproducibility
Wake 6:30 AM, 5 cycles: bedtime = 06:30 - (5*90+14) min = 10:46 PM.
Change log
- 2026-04-24: methodology page first published.
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