Health & Fitness calculators
Estimate body composition, energy needs, and training targets with the standard clinical and sports-science formulas.
- BMI CalculatorCalculate your body mass index from height and weight in metric or imperial units, see your BMI category, and find your healthy weight range.
- BMR CalculatorCalculate your basal metabolic rate with the Mifflin-St Jeor equation in metric or imperial units, and see daily calorie needs at four activity levels.
- TDEE CalculatorEstimate your total daily energy expenditure from height, weight, age, sex and activity level, plus the intake for losing or gaining weight.
- Body Fat CalculatorEstimate your body fat percentage with the US Navy tape method from height, neck, waist and hip measurements, in centimetres or inches.
- Ideal Weight CalculatorFind your ideal body weight from height and sex using the Devine, Robinson, Miller and Hamwi formulas, plus your healthy BMI weight range.
- Macro CalculatorTurn a daily calorie target into grams of protein, carbohydrate, and fat using a balanced, low-carb, or high-carb split. Shows the calories behind each macro.
- Water Intake CalculatorWork out how much water to drink each day from your body weight, exercise, and climate — in litres, millilitres, cups, and glasses.
- Heart Rate Zone CalculatorWork out your five heart rate training zones with the Karvonen method, using your age and resting pulse to set a target bpm range for every effort.
- One Rep Max CalculatorEstimate your one-rep max from a submaximal set using the Epley and Brzycki formulas, plus percentage training loads in kilograms or pounds.
- Running Pace CalculatorTurn a run distance and finishing time into pace per kilometre or mile, speed in km/h and mph, and predicted 5K, 10K, half and marathon times.
- Due Date CalculatorEstimate a due date from the last menstrual period using Naegele’s rule, adjusted for cycle length, with gestational age, trimester and milestones.
- VO2 Max CalculatorEstimate VO2 max from a Cooper 12-minute run, a 1.5-mile run, a Rockport walk test or your resting pulse, and see the fitness category for your age and sex.
- Waist-to-Hip Ratio CalculatorDivide your waist by your hips to see where you carry fat, check it against the WHO cut-offs of 0.90 and 0.85, and get your waist-to-height ratio.
- Body Surface Area CalculatorCalculate body surface area in m² from height and weight using the Mosteller, Du Bois, Haycock, Gehan & George and Boyd formulas side by side.
- Lean Body Mass CalculatorEstimate lean body mass from height, weight and sex with the Boer, James and Hume formulas side by side, plus fat mass and fat-free mass index.
- Ovulation CalculatorEstimate your ovulation date and six-day fertile window from your last period and cycle length, counted back from the next period rather than forward.
- Calories Burned CalculatorWork out the calories burned in one session from its MET value, your body weight and its length — with the gross and net figures shown separately.
- Caloric Deficit CalculatorTurn maintenance calories and a goal weight into a daily intake, a weekly rate and a date — with the 3,500-calorie rule shown against a model that adapts.
What a body measurement can and cannot tell you
Every metric here is an estimate produced by a formula fitted to a population, not a measurement of you. BMI is the clearest case: it is mass divided by height squared, a ratio devised in the 1830s as a population statistic. It says nothing about what the mass is made of, which is why a muscular athlete and a sedentary person of the same height and weight receive the same number and the number means something different in each case.
The same caution applies to body fat estimated from tape measurements, to ideal weight formulas that predate modern body composition research, and to any single threshold that sorts people into categories. These are useful for tracking change in one person over time, which is what they are good at. They are weak at classifying one person at one moment.
Energy: BMR, TDEE and what a deficit means
BMR is what the body uses at complete rest to run its basic functions — the floor, not the target. TDEE is BMR multiplied by an activity factor, and it is the figure that maintenance actually depends on. The Mifflin-St Jeor equation, used here, was fitted in 1990 and is generally more accurate for modern populations than the older Harris-Benedict equations it replaced, though both carry error bars of several hundred calories for any individual.
A deficit is simply intake below TDEE. The common rule that 3500 calories equals a pound of fat is a linear approximation that holds early and drifts later, because TDEE itself falls as body mass falls. This is why a deficit that worked for two months stops working in the third: the target moved.
Frequently asked questions
Is BMI accurate for athletes or very muscular people?
No, and this is its best known limitation. BMI uses only height and weight, so it cannot distinguish muscle from fat. Muscle is denser, so a well trained athlete frequently lands in the overweight or obese range while carrying low body fat. For that population a body fat estimate or a waist to hip ratio carries far more information. BMI remains useful for tracking one person over time, where the composition changes slowly and the trend is what matters.
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest — breathing, circulation, cell maintenance — measured over 24 hours doing nothing at all. TDEE is BMR multiplied by an activity factor that accounts for everything else: moving around, exercising, and the energy spent digesting food. TDEE is always the larger number and is the one to compare intake against. BMR is the floor beneath it.
Why do two calculators give me different calorie numbers?
Because they use different equations fitted to different populations. Mifflin-St Jeor, Harris-Benedict and Katch-McArdle each produce different figures for the same person, and Katch-McArdle needs a body fat estimate the others do not use. None is authoritative. The practical approach is to pick one, treat its output as a starting point, and adjust based on what actually happens to your weight over several weeks.
Can these replace advice from a doctor or dietitian?
No. Everything here is a published formula applied to numbers you typed, with no knowledge of your medical history, medications, or anything a clinician would ask about. The estimates are educational and are useful for framing a conversation, not for replacing one. Anything involving pregnancy, a medical condition, or a significant change in eating or training warrants a professional who can see the whole picture.