About Sleepyhours

What this site is

Sleepyhours is a small set of free, ad-free sleep calculators built by an independent developer. There is no company behind it, no signup, no upsell, and no data is collected beyond standard server logs. The calculators are built on published sleep research — they are decision aids, not medical advice.

Why it exists

Most sleep-calculator sites are content farms — short blurbs wrapped around a calculator widget, optimized for ad placement. They tend to recycle the same five facts about sleep cycles without ever pointing to the studies. Sleepyhours is an attempt to do the opposite: explain the math, name the sources, and answer the questions a thoughtful person would actually ask.

How the calculators work

The 90-minute sleep cycle model

The bedtime, wake-up, and nap calculators use the canonical 90-minute sleep cycle figure. This number is a population average. Real cycles range from roughly 80 to 110 minutes and tend to lengthen across the night, with more REM and less slow-wave sleep in the later cycles (Carskadon & Dement, in Principles and Practice of Sleep Medicine, 6th ed., 2017). The implication: the calculators get most adults within 10–15 minutes of optimal cycle alignment. They are not personalized.

Sleep onset latency

The calculators add 14 minutes for typical sleep onset (the time from getting in bed to actually falling asleep). Healthy adults fall asleep in 10–20 minutes; under 10 minutes consistently is a sign of sleep deprivation, over 30 minutes is a marker for insomnia worth taking seriously (American Academy of Sleep Medicine, clinical practice guidelines).

Caffeine half-life

The caffeine calculator uses a 5-hour half-life as the population default, which is the median value across pharmacokinetic studies. Real half-life varies from 1.5 hours (fast metabolizers, ~10% of population) to 9.5 hours (slow metabolizers, ~5%), driven primarily by the CYP1A2 gene (Blanchard & Sawers, 1983; Rodopoulos et al., 1995).

Melatonin timing (phase response curve)

The melatonin calculator uses the phase-response curve established by Burgess and colleagues. A low dose (0.3–0.5 mg) taken ~5 hours before DLMO (dim light melatonin onset) shifts the circadian rhythm earlier; taken ~9 hours before, it shifts later (Burgess et al., 2010, J Clin Endocrinol Metab).

Chronotype (rMEQ)

The chronotype quiz is the reduced Morningness-Eveningness Questionnaire — 5 questions, validated against the full 19-item MEQ (Adan & Almirall, 1991). It produces categories that correlate well with DLMO timing in clinical studies.

Sleep need by age

Recommended sleep durations come from the National Sleep Foundation 2015 expert panel (Hirshkowitz et al., 2015, Sleep Health) and the American Academy of Sleep Medicine consensus for children and adolescents (Paruthi et al., 2016). These are population ranges, not individual targets.

Sleep debt

The sleep debt model treats accumulated deficit linearly, which matches the dose-response findings of the chronic partial sleep deprivation literature (Van Dongen et al., 2003, Sleep). The study showed measurable, cumulative cognitive decline in adults restricted to 6 hours of sleep per night across 14 nights, with subjects unaware of the impairment.

What these calculators cannot do

They cannot diagnose. They cannot account for sleep disorders (insomnia, sleep apnea, restless legs, narcolepsy, REM sleep behavior disorder). They cannot account for medications affecting sleep architecture, shift-work disorder, or seasonal affective patterns. If you regularly cannot fall asleep, wake unrefreshed despite adequate time in bed, snore loudly or stop breathing during sleep, or experience excessive daytime sleepiness — see a sleep physician. The screening tools above can identify when sleep math is the problem; they cannot identify when sleep physiology is the problem.

Editorial standards

• Every quantitative claim links to or cites the source study.
• Population averages are labeled as averages, not personal recommendations.
• When the research is contested (e.g., the "you need exactly 8 hours" folklore), the page says so.
• Calculations are deterministic. Given the same inputs, the same outputs come out — no AI, no LLM, no probabilistic guessing.
• Content is reviewed when underlying research updates. Pages display a "last updated" date in the footer.

Who built this

Sleepyhours is built and maintained by a single independent developer with a long-standing interest in sleep science, not a medical professional. The calculations are based entirely on peer-reviewed literature; the prose is written from that literature. Errors are mine — if you find one, the issue tracker on the underlying calculation is open via the project repository (linked in footer once public).

Medical disclaimer

Nothing on this site is medical advice. The calculators are educational decision aids. If you have a sleep problem, consult a licensed sleep physician — a single sleep study (polysomnography) can identify disorders no calculator can. The information here is general; medical care is specific.

Privacy

No accounts. No personal data collected. No third-party tracking pixels, no Google Analytics, no Facebook Pixel. Server logs are retained briefly for security and abuse prevention, then discarded.