Health & Fitness Calculators

BMI, calories, body metrics, pregnancy and fitness calculators.

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The Health & Fitness calculators estimate body measurements, energy needs, pregnancy dates and training targets from standard published formulas. Each page names the formula it uses — for example Mifflin-St Jeor for calorie needs or Naegele's rule for due dates — so you know what kind of estimate you are looking at.

These are screening and planning tools. They do not diagnose any condition, and a result outside the usual range is a reason to speak to a doctor, not a conclusion.

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Fitness

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All Health & Fitness Calculators

Baby Age CalculatorCalculate your baby's exact age in years, months, weeks, and days from their date of birth.Baby Weight Gain CalculatorTrack your baby's average weight gain rate since birth, in grams per week and per day.BMI CalculatorCalculate your Body Mass Index (BMI) from your weight and height, and see which BMI category you fall into using WHO Asia-Pacific classification cutoffs.BMI Prime CalculatorCalculate your BMI Prime — the ratio of your BMI to the upper limit of the normal BMI range (25) — from your weight and height.BMR CalculatorEstimate your Basal Metabolic Rate (BMR) — the calories your body burns at rest — using the Mifflin-St Jeor equation, based on your weight, height, age, and sex.Body Fat CalculatorEstimate your body fat percentage using the U.S. Navy circumference (tape measurement) method, from your height, neck, waist, and (for women) hip measurements.Body Surface Area CalculatorCalculate your body surface area (BSA) using the Du Bois formula, based on your weight and height.Body Type CalculatorGet a quick body type (somatotype) estimate — Ectomorph, Mesomorph, or Endomorph — from your height and wrist circumference.Calorie CalculatorEstimate your Basal Metabolic Rate (BMR) and Total Daily Energy Expenditure (TDEE) using the Mifflin-St Jeor equation, based on your weight, height, age, sex, and activity level.Calorie Deficit CalculatorFind your daily calorie target for weight loss, based on your maintenance calories and desired weekly rate of weight loss.Calorie Surplus CalculatorFind your daily calorie target for weight or muscle gain, based on your maintenance calories and desired weekly rate of weight gain.Calories Burned CalculatorEstimate calories burned during an activity using the standard MET (Metabolic Equivalent of Task) formula, based on your weight and duration.Carbohydrate Intake CalculatorEstimate your daily carbohydrate intake in grams from your calorie target and the percentage of calories you want from carbs.Conception CalculatorEstimate your conception date and fertile window from the first day of your last menstrual period.Cycling Calories CalculatorEstimate calories burned while cycling, based on your weight and cycling duration.Distance to Steps CalculatorConvert a distance into an estimated step count, based on your stride length.Due Date CalculatorEstimate your pregnancy due date from the first day of your last menstrual period, using Naegele's rule.Fat Intake CalculatorEstimate your daily dietary fat intake in grams from your calorie target and the percentage of calories you want from fat.Fiber Intake CalculatorFind your recommended daily dietary fiber intake based on your age and sex, per the Institute of Medicine's Adequate Intake guidelines.Gestational Age CalculatorCalculate gestational age in weeks and days from the last menstrual period.GFR CalculatorEstimate your glomerular filtration rate (eGFR) — a measure of kidney function — using the 2021 CKD-EPI creatinine equation, from a serum creatinine lab result.Half Marathon Pace CalculatorCalculate the pace and speed needed to finish a half marathon (21.0975 km) in a target time.Healthy Weight CalculatorFind your healthy weight range based on the WHO normal BMI range (18.5-25) for your height.Heart Rate Zone CalculatorSee your five heart rate training zones (50-100% of max heart rate) based on your age.Ideal Body Fat CalculatorSee reference body fat percentage ranges (essential, athletes, fitness, acceptable) by sex, and classify your own body fat percentage against them.Ideal Weight CalculatorEstimate your ideal bodyweight using four classic clinical formulas — Devine, Robinson, Miller, and Hamwi — based on your height and sex.Lean Body Mass CalculatorEstimate your lean body mass (everything except fat mass) using the Boer formula, based on your weight, height, and sex.Macro CalculatorSplit a daily calorie target into protein, carbohydrate, and fat grams based on a chosen macro percentage split.Marathon Pace CalculatorCalculate the pace and speed needed to finish a marathon (42.195 km) in a target time.One Rep Max CalculatorEstimate your one-rep max (1RM) for a lift from the weight and reps you completed, using the Epley and Brzycki formulas.Ovulation CalculatorEstimate your ovulation date and fertile window from your last period and cycle length.Pace CalculatorCalculate your pace (minutes per km or mile) and speed from a distance and time.Period CalculatorPredict your next period date and fertile window from your last period and cycle length.Pregnancy CalculatorFind your due date, current week of pregnancy, and trimester from your last menstrual period.Pregnancy Trimester CalculatorFind out which trimester you're in from your last menstrual period.Pregnancy Week CalculatorFind out exactly how many weeks and days pregnant you are, from your last menstrual period.Pregnancy Weight Gain CalculatorFind your recommended total pregnancy weight gain range based on your pre-pregnancy BMI, per Institute of Medicine guidelines.Protein Intake CalculatorEstimate your recommended daily protein intake range based on your bodyweight and activity level.Race Time PredictorPredict your race time at a new distance from a recent race result, using Riegel's formula.Running Calories CalculatorEstimate calories burned while running, based on your weight and running duration.Running Speed CalculatorCalculate your running speed (km/h or mph) from a distance and time.Sleep CalculatorFind the best times to go to bed based on when you need to wake up, using 90-minute sleep cycles.Sleep Cycle CalculatorFind the best times to wake up based on when you go to bed, using 90-minute sleep cycles.Steps to Calories CalculatorEstimate calories burned from a step count and your bodyweight.Steps to Distance CalculatorConvert a step count into distance walked or run, based on your stride length.Swimming Calories CalculatorEstimate calories burned while swimming, based on your weight and swimming duration.Target Heart Rate CalculatorFind your target heart rate zone for exercise using the Karvonen formula, based on your age, resting heart rate, and desired intensity.TDEE CalculatorEstimate your Total Daily Energy Expenditure (TDEE) — the calories you burn per day including activity — using the Mifflin-St Jeor equation.Training Pace CalculatorGet easy, long-run, tempo, and interval training paces derived from your current race pace.VO2 Max CalculatorEstimate your VO2 max (aerobic fitness) using the Cooper 12-minute run test — the distance you cover in 12 minutes.Waist-to-Height Ratio CalculatorCalculate your waist-to-height ratio and see how it compares to the widely cited "keep your waist below half your height" guideline.Waist-to-Hip Ratio CalculatorCalculate your waist-to-hip ratio and see your cardiovascular risk category per WHO sex-specific thresholds.Walking Calories CalculatorEstimate calories burned while walking, based on your weight and walking duration.Water Intake CalculatorEstimate your recommended daily water intake based on your bodyweight and exercise duration.

BMI, body fat and waist measures answer different questions

BMI compares weight with height but cannot tell muscle from fat. Body-fat estimates address that, and waist-based ratios show where fat is carried. Using two of these together gives a fuller picture than any one number.

Formula-based estimates have a margin of error

Calorie needs, maximum heart rate and due dates are population averages applied to you. Real values vary from person to person — a due date, for example, is the midpoint of a range rather than the day labour is expected.

How these calculators work

Each calculator applies one named, published formula to the values you enter and shows that formula on its page. Some formulas differ by sex — the body fat calculator, for example, uses separate equations for men and women.

Limitations

  • Not medical advice and not a diagnosis; results are general estimates for adults unless a page says otherwise.
  • Formulas were developed on specific populations and can be less accurate for athletes, older adults, children and during pregnancy.

Frequently asked questions

Can these calculators diagnose a health condition?

No. They apply general formulas to the numbers you enter. A doctor or qualified health professional should interpret results that concern you, alongside tests and history.

Guide last updated 24-09-2026.

Health & Fitness Calculator Guides

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Health & Fitness2 min read

BMI vs Body Fat Percentage: Which Is a Better Health Indicator?

BMI is a quick screening tool based only on height and weight — it can't tell muscle from fat, so a muscular, athletic person can register as "overweight" or "obese" despite having very little body fat. Body fat percentage measures composition directly and is the more accurate indicator for an individual, but BMI remains useful as a fast, no-measurement population-level screen.

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Health & Fitness2 min read

How to Calculate Your Daily Calorie Needs (TDEE)

Your Total Daily Energy Expenditure (TDEE) is your Basal Metabolic Rate (BMR — the calories you'd burn at complete rest) multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (very active) — eating below TDEE creates a calorie deficit for weight loss, eating above it creates a surplus for weight gain.

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Health & Fitness2 min read

How Your Pregnancy Due Date Is Calculated (Naegele's Rule Explained)

The standard due-date estimate is simply the first day of your last menstrual period (LMP) plus 280 days (40 weeks) — a method called Naegele's rule — which counts from before conception actually happens, not from conception itself, which is why "40 weeks pregnant" doesn't mean 40 weeks since conception.

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Health & Fitness1 min read

Body Type Calculator: How the Height-to-Wrist Ratio Sorts Ectomorph, Mesomorph, Endomorph

Worked examples running the Body Type Calculator's real height-divided-by-wrist-circumference formula show exactly how three different ratios land in the Ectomorph, Mesomorph, and Endomorph bands.

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Health & Fitness2 min read

Body Type vs. Ideal Body Fat: Why Your Frame Isn't Your Composition

Running the same two people's real measurements through the Body Type Calculator and the Ideal Body Fat Calculator shows why a frame classification and a body-fat category are two independent readings, not steps in one pipeline.

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Health & Fitness2 min read

Heart Rate Training Zones Explained: The Five-Zone Model

The standard five-zone training model divides your estimated maximum heart rate (220 minus age) into five bands from 50% to 100%, each corresponding to a different training intensity and physiological effect — from easy recovery pace at the low end to maximum, unsustainable effort at the top.

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