Methodology & sources
Every number on this site is a model, and a model is only as honest as its assumptions. This page states the model, shows the arithmetic, lists the sources, and — just as importantly — says what we deliberately do not do.
Planning tool, not medical advice. These figures are population averages for scheduling your sleep — they don't diagnose or treat any condition. See a clinician for persistent sleep problems.
What model do all the calculators share?
Every calculator here is a view onto one model: your age sets a sleep need (the NSF age-banded ranges below), your chronotype shifts the timing of that sleep, and a target wake time anchors it. Bedtimes are derived, never guessed: wake time minus sleep need minus sleep latency, organised into cycles of configurable length. All clock maths runs in minutes-since-midnight with day-to-day arithmetic anchored at noon, so results survive daylight-saving transitions — a class of bug most sleep sites ship.
The arithmetic is shown on every tool with your own numbers substituted in. If a result can't show its working, we consider it unfinished.
What are the standing assumptions?
Cycle length defaults to 90 minutes and is adjustable from 60–120 — the published between-person range. Sleep latency defaults to 15 minutes (healthy range ~10–20) and is adjustable from 0–60. Sleep need uses the midpoint of the NSF recommended band as the working target, clamped to the panel's "may be appropriate" envelope so the tool cannot prescribe an extreme. REM estimates apply the textbook across-the-night curve and are labelled estimates — polysomnography is the only measurement. Sleep age is a transparent novelty composite, not a biomarker, and says so on its result card.
Why NSF ranges and not the CDC's?
Several competitors cite the CDC's sleep-duration guidance. That guidance is not a rival study — it republishes the American Academy of Sleep Medicine / Sleep Research Society consensus: a single "7 or more hours" floor for adults (Watson et al., 2015) and per-24-hour ranges for children from 4 months up (Paruthi et al., 2016). We build on the National Sleep Foundation's 2015 panel instead, because it publishes what a calculator actually needs: two-sided recommended ranges for adults (7–9 hours, not just "7+"), bands that split the first year of life into newborn and infant (the AASM guidance starts at 4 months), and an explicit "may be appropriate" envelope around every range — which is what lets our tools show a band and clamp a personal target without prescribing an extreme. The two efforts drew on much of the same evidence and overlapping experts; the difference is granularity, not science.
What do we deliberately not do?
No clinical screening instruments — no Epworth Sleepiness Scale, no STOP-BANG, no AHI estimator. Those are diagnostic territory, they belong with a clinician, and building them on a calculator site is a safety problem, not a feature gap. No supplement recommendations and no "sleepmaxxing stack" content. No medical claims of any kind: everything here is framed as planning and preference. And no email gates — every result is free, instant and computed in your browser.
Sources
[1] Sleep duration by age
Hirshkowitz M, Whiton K, Albert SM, et al. National Sleep Foundation's updated sleep duration recommendations: final report. Sleep Health. 2015;1(4):233–243.
Consensus of an 18-member expert panel convened from 12 stakeholder organisations, reviewing 300+ studies. The age-banded ranges and 'may be appropriate' envelopes on the sleep-need page are taken directly from this table.
[2] AASM/SRS consensus — the CDC's source
Watson NF, Badr MS, Belenky G, et al. Recommended amount of sleep for a healthy adult: a joint consensus of the AASM and SRS. Sleep. 2015;38(6):843–844. · Paruthi S, Brooks LJ, D'Ambrosio C, et al. Recommended amount of sleep for pediatric populations: AASM consensus statement. J Clin Sleep Med. 2016;12(6):785–786.
The consensus the CDC's sleep-duration guidance republishes — a '7 or more hours' floor for adults and per-24-hour ranges for children from 4 months. Cited for comparison: we build on the NSF 2015 panel for its two-sided ranges, newborn band and 'may be appropriate' envelopes (see 'Why NSF ranges and not the CDC's?').
[3] Sleep stages, cycle length, REM across the night
Carskadon MA, Dement WC. Normal human sleep: an overview. In: Principles and Practice of Sleep Medicine. 6th ed. Elsevier; 2017.
The standard reference for sleep architecture: ~90-minute average cycle length (range ~70–120 min), the deep-sleep-heavy early cycles, and the REM ramp from ~10 minutes in cycle 1 to 40–60 minutes in the final cycles.
[4] Sleep debt and partial restriction
Banks S, Dinges DF. Behavioral and physiological consequences of sleep restriction. J Clin Sleep Med. 2007;3(5):519–528.
The evidence that partial sleep restriction accumulates performance deficits, that subjective sleepiness under-reports the impairment, and that recovery is gradual across multiple nights — the reason our recovery plan is deliberately slow.
[5] Chronic restriction vs total deprivation
Van Dongen HPA, Maislin G, Mullington JM, Dinges DF. The cumulative cost of additional wakefulness. Sleep. 2003;26(2):117–126.
The dose–response study behind the 'two weeks of 6-hour nights ≈ one to two nights of total deprivation' claim: performance kept declining while subjects' self-ratings plateaued.
[6] Coffee naps
Horne JA, Reyner LA. Counteracting driver sleepiness: effects of napping, caffeine, and placebo. Psychophysiology. 1997;34(3):306–309. · Reyner LA, Horne JA. Suppression of sleepiness in drivers: combination of caffeine with a short nap. Psychophysiology. 1997;34(6):721–725.
The driving-simulator studies showing caffeine + a short nap outperforms either alone, and the ~20-minute caffeine-onset timing the protocol relies on.
[7] Warm-bath effect
Haghayegh S, Khoshnevis S, Smolensky MH, Diller KR, Castriotta RJ. Sleep Medicine Reviews. 2019;46:124–135.
Systematic review and meta-analysis of passive body heating: a 40–42 °C bath/shower 1–2 hours before bed shortened sleep-onset latency by ~10 minutes on average.
[8] Jet lag asymmetry and adjustment rates
Eastman CI, Burgess HJ. How to travel the world without jet lag. Sleep Med Clin. 2009;4(2):241–255.
The direction asymmetry (delays easier than advances) and the ~1 day/zone eastward, ~⅔ day/zone westward adjustment rule of thumb used by the jet lag calculator.
[9] The four-animal chronotype framing
Breus MJ. The Power of When. Little, Brown Spark; 2016.
Source of the lion/bear/wolf/dolphin framework. A popularisation, not a validated instrument — the research-grade tools are the Morningness–Eveningness Questionnaire (Horne & Östberg 1976) and the Munich ChronoType Questionnaire (Roenneberg 2003). We attribute the framing to Dr Breus and make no clinical-validity claim for the quiz.
[10] Sleep efficiency bands
Lichstein KL, Durrence HH, Taylor DJ, Bush AJ, Riedel BW. Quantitative criteria for insomnia. Behav Res Ther. 2003;41(4):427–445.
The ≤85% poor-efficiency convention used in research criteria; healthy adults cluster at 85–95%.
[11] CBT-I and sleep restriction
Trauer JM, Qian MY, Doyle JS, Rajaratnam SMW, Cunnington D. Cognitive behavioral therapy for chronic insomnia: a systematic review and meta-analysis. Ann Intern Med. 2015;163(3):191–204.
First-line treatment evidence referenced (not offered) on the efficiency page. We describe the mechanism; delivery belongs with a clinician.
The sleep-need table cites National Sleep Foundation (2015) directly on the page where it is rendered. Citations are provided for transparency; inclusion is not endorsement, and none of these sources are affiliated with this site.
Keep planning
Nap Calculator
Power nap, slow-wave or full cycle — the right nap length and its best window.
REM Sleep Calculator
How much REM a night actually contains, and why your last cycles hold most of it.
Sleep Age Calculator
A playful composite of how your sleep habits compare to your age. Honest about what it is.
Sleep Efficiency Calculator
Time asleep ÷ time in bed — the metric sleep clinics actually track.