Sources

We opened each document below on the official website of the organization named. Date checked: 2026-11-09. Each value was then checked against the original more than once. Guidance can change, so read the original again before an important decision.

BMI Calculator

• CDC: About Body Mass Index (BMI)
  BMI formula; what BMI does not measure · Reviewed 2025-12-16
• CDC: Adult BMI Categories
  Table "BMI categories for adults 20 and older" · Page dated 2024-03-19
• WHO Technical Report Series 894: Obesity: Preventing and Managing the Global Epidemic (2000)
  Table 2.1 Classification of adults according to BMI; section 2.3.2 · 2000
• WHO fact sheet: Obesity and overweight
  Definition of overweight and obesity, Adults · Page dated 2026-10-07
• WHO Expert Consultation: Appropriate body-mass index for Asian populations and its implications for policy and intervention strategies. The Lancet 2004;363:157-163 (abstract, via PubMed PMID 14726171)
  Abstract · 2004-01-10

Daily Calorie (Energy) Needs Calculator

• National Academies of Sciences, Engineering, and Medicine: Dietary Reference Intakes for Energy (2023)
  Table 5-16 (adult EER equations) and Table 5-4 (PAL categories) at this address; Summary Table S-1 at nap.nationalacademies.org/read/26818/chapter/2; Table 7-1 at nap.nationalacademies.org/read/26818/chapter/9 · 2023
• Institute of Medicine: Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids (2005)
  Chapter 5, Estimated Energy Requirement for adults 19 and older (book page 185) · 2005

Pregnancy Due Date Calculator

• ACOG (with AIUM and SMFM), Committee Opinion No. 700: Methods for Estimating the Due Date
  Body text: the EDD convention, accuracy of first-trimester ultrasound, redating thresholds · May 2017, reaffirmed 2025
• ACOG patient FAQ: How Your Fetus Grows During Pregnancy
  Length of pregnancy, trimesters, due dates · Last reviewed March 2026
• ACOG Committee Opinion No. 579: Definition of Term Pregnancy
  Early term, full term, late term, postterm · November 2013, reaffirmed 2025
• MedlinePlus (U.S. National Library of Medicine): Gestational age
  Normal length of pregnancy · Reviewed 2025-10-01
• StatPearls (NCBI Bookshelf, U.S. National Library of Medicine): Pregnancy Dating
  Naegele's rule · Last update 2022-09-12

Sleep Cycle Calculator

• NHLBI (NIH): Sleep Phases and Stages
  Length of a sleep cycle and number of cycles per night · Last updated 2022-03-24
• CDC: About Sleep
  Table of recommended hours of sleep by age group · Page dated 2024-05-15
• Watson NF 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
  Consensus recommendation for adults · Published 2015-06-01
• NHLBI (NIH): How Much Sleep Is Enough?
  Hours of sleep for adults · Last updated 2022-03-24
• MedlinePlus (U.S. National Library of Medicine): Healthy Sleep
  Hours of sleep for adults; consistent schedule · Last updated 2025-12-09

Daily Water Intake Reference

• Institute of Medicine (now National Academy of Medicine): Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate
  Chapter 4 Water: summary and Total Water AI summaries for ages 19 through 50 and 51+ · Published by the National Academies Press (cited as 2005)
• CDC: About Water and Healthier Drinks
  Meeting your water intake every day · Reviewed 2026-03-05

What we left out or assumed

• Time to fall asleep in the sleep calculator (default 15 minutes): this is an assumption made by the calculator. No official norm exists in the NHLBI, CDC, NHS or MedlinePlus pages we read. You can change it.
• The wording "subtract 3 months" for Naegele's rule: the source we could read describes the rule as adding 7 days and then 9 months, so we use that wording.
• Guidance that is limited to one organization is attributed to it by name. For example, the CDC's recommended sleep hours for ages 61 to 64 and 65+ draw on National Sleep Foundation recommendations, according to the CDC's own source list.
• The English edition has no age calculator, because how age is counted in law differs from country to country. Korea and Japan each have their own statutes, which the Korean and Japanese editions explain with their sources.