Health Calculators
Calculators for tracking health and fitness — BMI, calories, body fat, and pace.
Number of Calculators: 23
What to Know
Health calculators here fall into two groups: quick body-composition lookups (BMI, Body Fat, Waist-to-Hip Ratio, Ideal Weight) and calorie/activity planning (Calorie/TDEE, Macro, Calories Burned, Target Heart Rate). Every calculator in this category carries an honest limitations note about what a single formula can and can't capture — muscle mass, bone density, and individual variation all matter more than any one number.
Pregnancy and family planning get their own small cluster (Pregnancy Due Date, Pregnancy Weight Gain, Ovulation, Child Height Predictor), and Army Body Fat uses the current military standard rather than an older, retired formula. None of these replace a doctor's own assessment — they're a starting point for a conversation, not a diagnosis.
- Body Mass Index (BMI)Calculate your Body Mass Index (BMI), weight category, healthy weight range, BMI Prime, and Ponderal Index.
- Water IntakeEstimate how much water to drink daily based on your body weight, exercise, and climate.
- Pregnancy Due DateEstimate your due date and how far along you are, from your last period, conception date, or IVF transfer date.
- Pregnancy Weight GainFind your recommended total pregnancy weight gain range based on your pre-pregnancy BMI, using the IOM guidelines.
- Calorie / TDEEEstimate your Total Daily Energy Expenditure (TDEE) and calorie targets for weight loss (at three paces) or gain, with a choice of BMR formula.
- Body Fat PercentageEstimate your body fat percentage from height, neck, waist, and hip measurements using the U.S. Navy Circumference Method.
- Army Body FatEstimate your body fat percentage using the U.S. Army's current (2023-onward) one-site abdominal-circumference body composition worksheet (DA Form 5500/5501).
- Target Heart RateFind your target heart rate zones for exercise based on your age and resting heart rate.
- GFR / eGFREstimate your kidney function (eGFR) from a serum creatinine blood test result using the 2021 CKD-EPI race-free equation.
- OvulationEstimate your ovulation date, fertile window, and next expected period from the first day of your last period and your average cycle length.
- MacroSplit a daily calorie target into protein, carb, and fat grams using a common diet-style split (balanced, low-carb, high-protein, keto) or your own custom percentages.
- Protein IntakeFind your recommended daily protein range from your body weight and activity level, using commonly-cited sports nutrition guidance.
- Ideal WeightEstimate a reference body weight from your height and gender using four published formulas (Devine, Robinson, Miller, and Hamwi) plus their average.
- Calories BurnedEstimate calories burned during exercise from the activity, your body weight, and how long you did it, using standard MET values.
- Blood Alcohol Content (BAC)Estimate blood alcohol content from the number of standard drinks, body weight, biological gender, and time elapsed, using the Widmark formula.
- Lean Body MassEstimate your lean body mass (weight minus fat mass) from height, weight, and gender using three published formulas (Boer, James, and Hume) plus their average.
- Body Surface AreaEstimate your body surface area (BSA) from height and weight using three published formulas (DuBois, Mosteller, and Haycock) plus their average.
- Body Frame SizeEstimate your skeletal body frame size (small, medium, or large) from your height-to-wrist-circumference ratio.
- Waist-to-Hip RatioFind your waist-to-hip ratio and where it falls on a commonly-cited health-risk scale built on WHO guidance.
- Waist-to-Height RatioFind your waist-to-height ratio (WHtR) and see whether it falls in the commonly-cited healthy range — the same threshold for everyone, regardless of sex.
- Sleep DebtTotal up your accumulated sleep debt (or surplus) across a series of nights against your target nightly sleep need.
- Average Height ComparisonSee how your height compares to the average for your age and gender.
- Child Height PredictorEstimate a child's likely adult height from both parents' heights using the mid-parental height method.
Guided Journeys
Some of these calculators are also part of a guided journey — a connected chain that carries your numbers forward automatically. A journey may include steps from other categories too.
Fitness Nutrition Journey
Start Journey →A macro split is only as useful as the calorie target it's built on. This journey starts by working out your daily calorie target from the Calorie/TDEE Calculator -- based on your body, activity level, and goal -- then carries that figure straight into the Macro Calculator so your protein, carb, and fat targets are built on your own maintenance calories instead of a round number you picked yourself.
- Find Your Daily Calorie Target
- Split Your Calories Into Protein, Carbs, and Fat