Health
Browse 7 professional tools
Blood Alcohol Calculator
BMI Calculator
Body Fat Calculator
Calorie Calculator
Pregnancy Due Date Calculator
Sleep Calculator
Water Intake Calculator
Health tools cover the routine arithmetic of personal health — BMI, calorie needs, water intake, sleep cycle alignment, pregnancy due date. None of these diagnose anything; they are inputs to your own decision-making and to conversations with clinicians. Treat outputs as estimates within ±10-15% of clinical-grade measurement.
Body composition
BMI is criticized but still useful as a population-level screening number; pair with waist-to-height ratio for individual interpretation. US Navy tape method and Jackson-Pollock skinfold are practical body-fat estimators; DXA scan is gold standard if accuracy matters.
Calculate Body Mass Index (BMI) with height and weight. Get health category (underweight, normal, overweight, obese). Free online BMI calculator
Estimate body fat percentage using US Navy method or BMI. Calculate fat mass and lean mass. Free body composition calculator
Nutrition & metabolism
TDEE via Mifflin-St Jeor (most accurate predictive equation per 2005 ADA review), with macro-suggestion ranges. Water intake math distinguishing fluid from total water (food provides 20-30% for typical diets). BAC via Widmark formula.
Calculate daily calorie needs (TDEE) based on age, weight, height, and activity level. Get macro recommendations. Free TDEE calculator
Calculate how much water you should drink daily based on weight, activity, and climate. Free hydration calculator
Estimate BAC from drinks consumed. Widmark formula, multiple drink types, time to sober up, legal limits by country. Free online BAC calculator
Sleep & recovery
90-minute cycle alignment for wake times that avoid sleep inertia. Cycle length varies 75-110 minutes between individuals; the calculator uses the population average. For tracking actual cycles, wearables (Oura, Whoop) estimate via heart rate and motion.
Calculate optimal bedtime and wake times based on 90-minute sleep cycles. Sleep debt calculator, chronotype quiz, sleep recommendations by age
Free Pomodoro technique timer for productivity. 25-minute work sessions with 5-minute breaks. Customizable focus timer with notifications
Reproductive health
Naegele's rule (LMP + 280 days), with notes that only ~5% of births happen on the exact due date; realistic window is 38-41 weeks. For IVF pregnancies, calculate from embryo transfer date for higher accuracy.
Frequently asked questions
Is BMI a useful number?
For population screening: yes. For individual diagnosis: limited. BMI does not distinguish muscle from fat, doesn't adjust for frame size or ethnicity. WHO recommends lower thresholds for South/East Asian populations (overweight at 23, obese at 27.5). Always pair with at least one other metric.
How many calories should I eat?
TDEE (Total Daily Energy Expenditure) is the maintenance target. Subtract 300-500 for sustainable weight loss; add 200-300 for lean muscle gain. The Calorie Calculator uses Mifflin-St Jeor; expect ±10-15% accuracy. Track for 2 weeks against actual weight change to calibrate.
Is 8 glasses of water a day real?
The "8 glasses" is folklore. IOM recommendations are 3.7 L / 2.7 L total water (men / women) — including from food (~20-30% of intake) and all beverages (coffee, tea, milk all count). Thirst is a reliable guide for most adults under 60; for older adults and during exercise, drink on schedule.
What does "due date" really mean?
A point estimate from LMP + 280 days, with about 38-41 weeks as the realistic birth window. Only ~5% of babies arrive on the exact due date. For dating accuracy, first-trimester ultrasound (±5 days) beats LMP (±2 weeks) for women with irregular cycles.
Last updated · E-Utils editorial team