Health Calculators
The health calculators here turn published formulas and official guidance into quick, clear estimates. They cover body measurements, energy needs, hydration, exercise, fertility, pregnancy dates and sleep:
- Body size and composition: the BMI calculator uses the CDC’s adult categories, the body fat calculator uses the US Navy circumference method, and the ideal weight calculator compares the Hamwi, Devine, Robinson and Miller formulas with a healthy-BMI weight range.
- Energy and nutrition: the BMR calculator uses the Mifflin–St Jeor equation, the calorie calculator uses the National Academies’ estimated energy requirement equations, and the water intake calculator shows the National Academies’ adequate intakes of total water.
- Fitness: the target heart rate calculator gives moderate and vigorous exercise zones from the American Heart Association’s age-based method.
- Fertility and pregnancy: the ovulation calculator estimates ovulation and the fertile window for the next three cycles using ACOG’s calendar method, and the due date calculator works from the last menstrual period, conception date or IVF transfer date.
- Sleep: the sleep calculator times bedtimes and alarms around sleep cycles.
Health information has to be handled carefully, so every page in this section follows the same rules. The formula is written out in full, so you can see exactly how a result is produced. Every figure is cited to a source such as the CDC, the National Academies, ACOG or the original published study. Each page also shows the date it was last reviewed.
All of these tools give population-level estimates. Formulas like BMI and BMR describe averages, and they can be off for individuals, for example for athletes, older adults or people with certain medical conditions. Treat the results as a starting point, not a measurement.
These calculators are for general information. They don’t diagnose, treat or replace advice from a doctor, dietitian or midwife. For decisions about weight, diet, pregnancy or sleep problems, talk to a qualified health professional.
All Health Calculators (10 calculators)
Body Measurements
Nutrition & Hydration
Fitness & Exercise
Sources
- CDC, Adult BMI Categories — healthy weight is a BMI of 18.5 to less than 25 for adults 20 and older
- Hodgdon JA, Beckett MB. Prediction of percent body fat for U.S. Navy men and women from body circumferences and height. Naval Health Research Center, 1984 (DTIC ADA143890)
- Hodgdon and Beckett, Naval Health Research Center, 1984 (DTIC ADA146456)
- Naval Health Research Center report noting that many sailors question the accuracy of the Navy body fat equations (DTIC ADA370117)
- Equation coefficients as published by Topend Sports, citing Hodgdon and Beckett (1984); all measurements in inches.
- Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241–247.
- Institute of Medicine. Dietary Reference Intakes for Energy, Carbohydrate, Fiber, Fat, Fatty Acids, Cholesterol, Protein, and Amino Acids. Washington, DC — National Academies Press, 2005.
- Statistics Canada, Health Reports 82-003-X (2008), Table 1 — IOM EER equations and physical activity coefficients for adults 19+, BMI 18.5–25 and BMI over 25
- National Academies (Institute of Medicine). Dietary Reference Intakes for Water, Potassium, Sodium, Chloride, and Sulfate. Washington, DC — National Academies Press, 2005.
- Dietary reference values for total water, including pregnancy (3.0 L/day) and lactation (3.8 L/day) — summary table in Nutrients 2018;10(12):1928
- VOA Special English Health Report, March 2, 2004 — coverage of the IOM report; most healthy people meet their daily fluid needs by letting thirst be their guide
- American Heart Association — Target Heart Rates Chart (maximum heart rate about 220 minus age; moderate about 50–70% and vigorous about 70–85% of maximum; resting heart rate 60–100 bpm)
- U.S. Department of Health and Human Services — Physical Activity Guidelines for Americans, 2nd edition (150 minutes moderate or 75 minutes vigorous aerobic activity a week)
- Sleep Foundation, Stages of Sleep — cycles average about 90 minutes; first cycle 70–100 minutes, later cycles 90–120 minutes; four to six cycles a night
- Sleep Foundation, How Long Should It Take to Fall Asleep? — most people fall asleep within 15–20 minutes
- CDC, FastStats — Sleep in Adults (adults need at least 7 hours of sleep a day)
- American College of Obstetricians and Gynecologists. Committee Opinion No. 700, Methods for Estimating the Due Date. Obstetrics & Gynecology 2017 (reaffirmed 2022)
- American College of Obstetricians and Gynecologists (ACOG) — Fertility Awareness-Based Methods of Family Planning, FAQ (ovulation about 14 days before the next period; fertile from 5 days before to 1 day after ovulation; egg and sperm survival)
- Office on Women's Health, U.S. Department of Health and Human Services — Trying to conceive (fertile window and variation in ovulation timing)