Topical hub
Free Health & Fitness Calculators
Body composition, nutrition, training load and clinical ratios, semantically linked.
53 calculators across 5 semantic clusters — free forever, instant results, downloadable PDF reports.
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Health calculators turn measurements into ratios and rates that can be compared against population norms. Height and weight become BMI; weight and activity become energy expenditure; circumference measurements become body-fat and risk estimates. The underlying pattern is the same: normalise a raw measurement so it can be interpreted.
Energy sits at the centre of the hub. Basal metabolic rate (BMR) is what your body spends at rest; multiplying it by an activity factor gives total daily energy expenditure (TDEE); comparing TDEE with intake gives the surplus or deficit that drives weight change. Macro, protein, carbohydrate and fat tools then split that energy target into grams.
Body composition tools answer a different question from body weight. BMI is a screening ratio, not a diagnosis; body fat percentage, lean body mass, FFMI and waist-to-height ratio describe what the weight is made of and where it sits, which correlates far better with metabolic risk.
Training and cardiovascular tools convert effort into prescribable numbers: maximum and target heart rate define intensity zones, VO2 max estimates aerobic capacity, and pace, split and race-prediction tools translate capacity into a schedule you can execute.
Everything here is an estimate built on population equations. They are useful for tracking direction and change over time; they are not a substitute for clinical measurement or medical advice.
Calculator directory
Body Composition
What body mass is made of and how it is distributed.
Free BMI Calculator
Body Mass Index from height and weight, in metric or US units.
Free Ideal Weight Calculator
Ideal body weight range from height and sex using multiple formulas.
Free Overweight Calculator
How many pounds you are above a healthy BMI range.
Free Body Fat Calculator
Estimate body fat percent from body measurements (US Navy method).
Free Lean Body Mass Calculator
Estimate lean body mass using the Boer formula.
Free Body Surface Area Calculator
BSA by Du Bois, Mosteller and Haycock formulas.
Free Waist to Hip Ratio Calculator
WHR and the health risk band it falls in.
Free Child Height Predictor
Estimate adult height from parents' heights.
Free Army/Navy Body Fat Calculator
Body fat percentage using the U.S. military circumference method.
Free Child BMI Percentile Calculator
Approximate BMI percentile for children and teens.
Free FFMI Calculator
Fat-Free Mass Index to gauge muscularity.
Free Waist-to-Height Ratio Calculator
A simple screen for central obesity risk.
Nutrition & Diet
Energy targets and macronutrient planning.
Free BMR Calculator
Basal Metabolic Rate from the Mifflin–St Jeor equation.
Free TDEE Calculator
Total Daily Energy Expenditure from BMR and activity level.
Free Calorie Calculator
Daily calorie needs for maintenance, cutting, and bulking.
Free Macro Calculator
Protein, carbs, and fat targets from calorie intake.
Free Protein Calculator
Daily protein target in grams based on body weight and activity.
Free Fat Intake Calculator
Recommended daily fat grams from calorie target.
Free Carbohydrate Calculator
Daily carb grams from your calorie target.
Free Sugar Intake Calculator
AHA-recommended daily added sugar limit.
Free Water Intake Calculator
Daily water needs based on weight and activity.
Free Calories Burned Calculator
Energy burned by activity using MET values.
Free Steps to Calories Calculator
Convert daily step count into calories and distance.
Free A1C to Average Glucose Calculator
Convert HbA1c percentage to estimated average glucose.
Free TDEE for Athletes Calculator
Total daily energy expenditure adjusted for training volume.
Free Caffeine Half-Life Calculator
How much caffeine remains in your system over time.
Free Calorie Deficit Calculator
Daily deficit needed to lose weight at your target rate.
Free Cholesterol Ratio Calculator
Total cholesterol to HDL ratio and cardiovascular risk indicator.
Free Goal Weight Date Calculator
The calendar date you'll likely hit your goal weight.
Free Treadmill Incline Calories Calculator
Calories burned adjusting for treadmill incline.
Free Walking Calories Calculator
Calories burned walking at a given speed and duration.
Free Weight Loss Timeline Calculator
Estimate how long it will take to reach your goal weight.
Fitness & Training
Intensity, capacity and performance prediction.
Free Target Heart Rate Calculator
Training zones from age using the Karvonen method.
Free Heart Rate Zones Calculator
Training zones from your max heart rate.
Free One Rep Max Calculator
Estimate 1RM from a submaximal lift (Epley formula).
Free Pace Calculator
Running pace, time, or distance — solve for any of the three.
Free Cycling Power/Speed Calculator
Estimate cycling speed from power output.
Free Heart Rate Recovery Calculator
Gauge cardiovascular fitness from post-exercise heart rate drop.
Free Marathon Time Predictor
Predict your marathon finish from a recent race result.
Free Max Heart Rate Calculator
Estimated maximum heart rate using multiple formulas.
Free Running Pace Splits Calculator
Even-pace splits for any race distance.
Free Swimming Pace Calculator
Pace per 100m/yards and projected race times.
Free VO2 Max Calculator
Estimate aerobic fitness from a timed run.
Pregnancy & Women's Health
Cycle, conception and gestation timelines.
Free Pregnancy Due Date Calculator
Estimated due date from last menstrual period (Naegele's rule).
Free Ovulation Calculator
Estimate ovulation and fertile window from cycle length.
Free Pregnancy Weight Gain Calculator
Recommended pregnancy weight gain range.
Free Menstrual Cycle Length Calculator
Average cycle length and predicted next period from recent cycles.
Clinical & Medical Metrics
Laboratory and screening ratios.
Free BAC Calculator
Estimated blood alcohol content by the Widmark formula.
Free Smoking Cost Calculator
Lifetime money spent on cigarettes.
Free Blood Pressure Category Calculator
Classify blood pressure reading using AHA categories.
Free Creatinine Clearance Calculator
Cockcroft-Gault estimate of creatinine clearance.
Free eGFR Calculator
Estimated glomerular filtration rate (kidney function) using CKD-EPI.
Free Sleep Cycle Bedtime Calculator
Best bedtimes or wake times based on 90-minute sleep cycles.
Key concepts in health calculators
- BMR
- Basal metabolic rate — energy burned at complete rest, typically from the Mifflin-St Jeor equation.
- TDEE
- Total daily energy expenditure — BMR multiplied by an activity factor covering movement, exercise and digestion.
- Energy balance
- Intake minus expenditure. A sustained deficit drives fat loss; a sustained surplus drives gain.
- BMI
- Weight in kilograms divided by height in metres squared — a screening ratio, not a body-composition measure.
- Body fat percentage
- Fat mass as a share of total mass, estimated from skinfolds, circumferences or impedance.
- Lean body mass
- Total mass minus fat mass; the tissue that drives resting metabolic rate.
- Macronutrients
- Protein (4 kcal/g), carbohydrate (4 kcal/g) and fat (9 kcal/g) — the split of an energy target.
- Maximum heart rate
- The theoretical ceiling of cardiac output, commonly estimated as 220 − age or the Tanaka formula.
- VO2 max
- Maximal oxygen uptake in ml/kg/min, the standard marker of aerobic fitness.
- Waist-to-height ratio
- Waist circumference divided by height; values above 0.5 signal elevated central adiposity risk.
How this topic works
How energy expenditure is estimated
Mifflin-St Jeor is the current default for BMR: for men, 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women the constant is −161. Multiplying by an activity factor between 1.2 (sedentary) and 1.9 (very heavy training) produces TDEE. The activity multiplier is the largest source of error — people routinely overestimate it — so if measured weight change disagrees with the projection, adjust the multiplier rather than the equation.
Why weight change lags energy balance
A pound of body fat stores roughly 3,500 kcal, so a 500 kcal daily deficit predicts about a pound a week. In practice, glycogen and water shifts mask the trend for the first one to two weeks, and adaptive thermogenesis reduces expenditure as weight falls. Weekly averages are the honest reading; daily scale numbers are noise.
Reading body composition properly
Two people at the same BMI can carry very different fat mass. A muscular athlete is routinely classified overweight by BMI alone. Pairing BMI with body fat percentage, waist-to-height ratio and lean body mass gives a far more usable picture, and FFMI normalises lean mass for height so training progress can be judged independently of scale weight.
Setting training intensity from heart rate
Estimate maximum heart rate, then work in zones: 50–60% for recovery, 60–70% for aerobic base, 70–80% for tempo, 80–90% for threshold and above 90% for VO2 max work. The Karvonen method uses heart rate reserve (max minus resting) instead of raw max, which personalises the zones for anyone with an unusually high or low resting rate.
Protein, distribution and adherence
Protein targets typically run 1.6–2.2 g per kg of bodyweight for people training with resistance, higher in a deficit to protect lean mass. Distribution across three to five feedings improves the muscle protein synthesis response, but total daily intake and long-run adherence dominate the outcome — which is why the macro and calorie tools here anchor on daily totals first.
Frequently asked questions
Is BMI a reliable measure of health?
BMI is a screening tool for populations, not a diagnosis for individuals. It ignores body composition and fat distribution, so pair it with body fat percentage and waist-to-height ratio before drawing conclusions.
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest. TDEE is BMR multiplied by an activity factor, so it includes daily movement, exercise and the thermic effect of food — TDEE is the number to compare intake against.
How large should a calorie deficit be?
A deficit of roughly 15–25% below TDEE, or about 500 kcal per day, targets about a pound of loss per week while remaining sustainable. Larger deficits accelerate lean mass loss and adherence failure.
How accurate are body fat estimates from measurements?
Circumference-based methods carry roughly a 3–4% margin against DEXA. They are far more useful for tracking change over time in one person than for comparing two people.
Which heart rate formula should I use?
The Tanaka formula (208 − 0.7 × age) fits adults better than the classic 220 − age, particularly over 40. If you know your resting heart rate, the Karvonen reserve method personalises zones further.
Do these calculators replace medical advice?
No. They are estimation tools built on population equations. Clinical metrics such as eGFR, creatinine clearance or blood pressure categories should be interpreted by a clinician using measured lab values.
How often should I recalculate my targets?
Recalculate after roughly every 5–10 lb of weight change or when training volume shifts substantially, since BMR scales with body mass and TDEE with activity.
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