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SleepTools

Methodology

How SleepTools calculators work.

Every formula on this site is attributed to a published source. This page lists what each calculator does, the science it's built on, and what it doesn't try to do.

Editorial review by the SleepTools Editorial Team. Last reviewed May 5, 2026.

Editorial principles

  • Every calculator is built on peer-reviewed sleep research, or a consensus guideline from the NSF, AAP, AASM, or CDC.
  • When the research gives a range (caffeine half-life is 5 to 9 hours, for example), the variable is exposed in the calculator so you can match it to your own metaboliser type.
  • Calculators do not diagnose sleep disorders. Any page that gives timing guidance carries a "Not medical advice" footer.
  • All calculations run in the browser. No data leaves your device, and no account is required.

Timing calculators

Sleep Cycle Calculator

Sleep cycle math uses the standard 90-minute cycle (Kleitman & Dement, 1957 polysomnography research) plus a 14-minute average sleep-onset latency (National Sleep Foundation).

Sources

  • Kleitman & Dement, 1957: REM cycle polysomnography
  • National Sleep Foundation: sleep-onset latency norms

Bedtime Calculator

Bedtime targets are computed back from a desired wake time using the 90-minute cycle (Kleitman & Dement, 1957) and a 14-minute sleep-onset latency buffer (National Sleep Foundation), then cross-referenced with NSF 2015 age-based duration guidelines.

Sources

  • Kleitman & Dement, 1957: REM cycle polysomnography
  • National Sleep Foundation, 2015: age-based sleep duration consensus

Wake-Up Time Calculator

Wake-time targets are end-of-cycle markers based on the 90-minute cycle (Kleitman & Dement, 1957), so you wake from light NREM rather than mid-cycle deep sleep. That is the model behind reduced sleep inertia.

Sources

  • Kleitman & Dement, 1957: REM cycle polysomnography
  • Tassi & Muzet, 2000: sleep inertia review

Nap Calculator

Nap durations are tied to sleep-stage progression: power naps end before N3 onset (~20 minutes per Lovato & Lack, 2010); 90-minute cycle naps complete a full cycle (Kleitman & Dement, 1957). NASA's flight-deck research validated the 26-minute optimum for alertness.

Sources

  • Lovato & Lack, 2010: sleep inertia and nap length
  • NASA-Ames, 1995: Flight Crew Nap Study (Rosekind et al.)
  • Kleitman & Dement, 1957: sleep cycle structure

Caffeine Cutoff Calculator

Caffeine cutoff times are derived from caffeine's pharmacokinetic half-life: 5 to 7 hours in normal CYP1A2 metabolizers, extending to 9 or more hours in slow metabolizers. Drake et al. (2013) found that caffeine taken 6 hours before bed reduced sleep by about an hour.

Sources

  • Drake et al., 2013: Caffeine effects on sleep taken 0, 3, or 6 h before going to bed
  • Institoris et al.: CYP1A2 metabolizer phenotypes

Health calculators

Sleep Debt Calculator

Sleep debt is the cumulative deficit between actual and recommended sleep (NSF 2015 age-based norms). Recovery adds about 1 extra hour per night above need (Banks & Dinges, 2007), capped at the recovery timelines reported in restriction-recovery studies.

Sources

  • Banks & Dinges, 2007: Behavioral and physiological consequences of sleep restriction
  • National Sleep Foundation, 2015: sleep duration recommendations

How Much Sleep Do I Need

Recommendations come from the National Sleep Foundation 2015 consensus statement, cross-referenced with the CDC and the American Academy of Pediatrics: 7 to 9 hours for adults 18 to 64, 8 to 10 hours for teens 13 to 17, 9 to 11 hours for children 6 to 12, and 7 to 8 hours for adults 65 and over.

Sources

  • Hirshkowitz et al. (NSF), 2015: National Sleep Foundation's sleep time duration recommendations
  • Centers for Disease Control and Prevention: sleep duration by age
  • American Academy of Pediatrics: pediatric sleep guidance

Sleep Deprivation Cost Calculator

Cognitive and economic costs are based on Belenky et al. (2003) on dose-dependent vigilance decline, and Hafner et al. (2017, RAND), which estimated $411B in annual U.S. economic loss from insufficient sleep.

Sources

  • Belenky et al., 2003: Patterns of performance degradation during sleep restriction
  • Hafner et al., 2017 (RAND): Why sleep matters: the economic costs of insufficient sleep

Sleep Quality Score

The score is calibrated against the Pittsburgh Sleep Quality Index domain structure (Buysse et al., 1989): subjective quality, latency, duration, efficiency, disturbances, medication use, and daytime dysfunction.

Sources

  • Buysse et al., 1989: The Pittsburgh Sleep Quality Index (PSQI)

Life-situation calculators

Baby Sleep Calculator

Wake windows and total sleep needs follow NSF 2015 and AAP age-based guidance: newborns 14 to 17 hours, infants 12 to 15 hours, toddlers 11 to 14 hours. Cross-checked against published Huckleberry developmental wake-window data.

Sources

  • American Academy of Pediatrics: recommended infant and toddler sleep durations
  • Hirshkowitz et al. (NSF), 2015: sleep duration recommendations
  • Huckleberry: published age-based wake-window data

Shift Work Sleep Calculator

Shift transitions use the AASM-validated circadian advance/delay limits (≈30 min/day advance, ≈60 min/day delay) and the Eastman & Burgess phase-shift protocols.

Sources

  • Eastman & Burgess, 2009: How to travel the world without jet lag
  • American Academy of Sleep Medicine: clinical practice guidelines for shift work disorder

Jet Lag Calculator

Recovery uses the standard adaptation rate of 1 day per time zone eastward and 1.5 days per zone westward, with light-exposure timing based on Eastman & Burgess (2009) and Sack (2010).

Sources

  • Eastman & Burgess, 2009: How to travel the world without jet lag
  • Sack, 2010: Jet lag (NEJM clinical review)

Circadian & chronotype calculators

Chronotype Calculator

Scoring follows the Morningness-Eveningness Questionnaire (Horne & Östberg, 1976), with the four-type Lion / Bear / Wolf / Dolphin classification described in Breus, 2016.

Sources

  • Horne & Östberg, 1976: A self-assessment questionnaire to determine morningness-eveningness
  • Breus, 2016: The Power of When (chronotype classification)

Sleep Schedule Fixer

Schedule shifts use the Eastman & Burgess phase-advance and phase-delay protocols, capped at the safe rate of ≈30 min/day advance and ≈60 min/day delay (American Academy of Sleep Medicine).

Sources

  • Eastman & Burgess, 2009: How to travel the world without jet lag
  • American Academy of Sleep Medicine: circadian rhythm sleep–wake disorder guidelines

Melatonin Timing Calculator

Timing is set against dim-light melatonin onset (DLMO, about 2 hours before habitual sleep) per Lewy et al. (2006). Low-dose melatonin (0.3 to 1 mg) taken 3 to 5 hours before desired sleep onset shifts circadian phase forward (Burgess & Emens, 2016).

Sources

  • Lewy et al., 2006: The dim-light melatonin onset (DLMO) as a marker of circadian phase
  • Burgess & Emens, 2016: Drugs used in circadian sleep–wake rhythm disturbances
  • Brzezinski et al., 2005: Effects of exogenous melatonin on sleep: meta-analysis

Alcohol and Sleep Calculator

BAC is computed via the Widmark formula. REM-suppression effects use Ebrahim et al. (2013), a meta-analysis finding that alcohol increases SWS in the first half of the night and suppresses REM, with effects scaling roughly with dose.

Sources

  • Ebrahim et al., 2013: Alcohol and sleep I: effects on normal sleep (meta-analysis)
  • Widmark, 1932: formula for blood alcohol concentration estimation

Teen Sleep Calculator

Targets reflect the puberty-driven circadian phase delay documented by Carskadon, and the AASM and AAP recommendation that schools start no earlier than 8:30 a.m. for adolescents, who need 8 to 10 hours of sleep.

Sources

  • Carskadon et al.: adolescent circadian phase delay research
  • American Academy of Sleep Medicine: adolescent sleep duration position statement
  • American Academy of Pediatrics: school start times policy statement

Sleep Banking Calculator

Banking schedules follow the Rupp et al. (2009) protocol: sleeping about 2 hours longer each night for one week before a planned sleep restriction reduces the cognitive cost during the restriction period.

Sources

  • Rupp, Wesensten & Balkin, 2009: Banking sleep: realization of benefits during subsequent sleep restriction and recovery

Limitations

These tools model averaged sleep physiology for healthy adults, or for healthy children where applicable. Individual sleep cycles run 80 to 110 minutes. Caffeine half-life varies more than threefold by metaboliser type, age, hormonal contraceptive use, and pregnancy. Melatonin DLMO can shift by several hours depending on chronotype. The calculators expose these variables wherever they change the result enough to matter.

SleepTools does not diagnose insomnia, delayed sleep phase syndrome, shift work disorder, or any other sleep disorder. If you have persistent sleep difficulties, see a board-certified sleep medicine physician.

How this page is maintained

When a calculator's formula changes, the corresponding entry in lib/content/citations.ts is updated in the same commit. That single source feeds this page, the "Built on" footer on each calculator, and the /llms.txt file that AI search engines read.

These tools are for informational purposes only and are not a substitute for medical advice. For sleep disorders or persistent sleep difficulties, consult a healthcare provider.