Health calculators are digital tools that use clinically validated mathematical formulas to give you instant, personalised health metrics — without needing to visit a doctor for basic assessments. Whether you want to know if your weight is healthy, how many calories to eat to lose 10 kg, or when your baby is due, our free health calculators give you accurate answers in seconds.
Trusted by fitness coaches, nutritionists, nurses, and everyday users in the USA, UK, Canada, Australia, Germany, and 150+ other countries, FinanceKit Pro's health suite covers every major body metric with both metric (kg, cm) and imperial (lbs, feet, inches) support.
BMI Calculator — Formula & How to Interpret Your Score
Body Mass Index (BMI) is calculated by dividing your weight (kg) by your height in metres squared:
The WHO classifies BMI into five ranges: underweight (<18.5), normal (18.5–24.9), overweight (25–29.9), Obese Class I (30–34.9), and Obese Class II+ (≥35). While BMI does not measure body fat directly, it is the most widely used screening tool for healthy weight globally. For a more precise body composition assessment, pair it with our Body Fat Calculator.
Calorie Calculator — TDEE, BMR, and Weight Management
Your Total Daily Energy Expenditure (TDEE) is the total calories your body burns in a day, including exercise. The Mifflin-St Jeor formula — the gold standard used by dietitians — first calculates your BMR:
To lose 0.5 kg per week, eat 550 kcal below your TDEE. To lose 1 kg per week, eat 1,100 kcal below. Never go below 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision.
Body Fat % Calculator — US Navy Method Explained
The US Navy circumference method estimates body fat using simple tape measurements — no scales or gym equipment needed. For men, it uses neck and waist circumference. For women, it also includes hip circumference. The formula uses natural logarithms and has an accuracy of ±1–3% compared to DEXA scans, making it the best free at-home method available. Healthy body fat ranges are 10–20% for men and 18–28% for women (American Council on Exercise standards).
Pregnancy Due Date — How Naegele's Rule Works
Naegele's Rule (developed in 1812 and still used worldwide) calculates estimated due date (EDD) by adding 280 days to the first day of your last menstrual period. Assuming a standard 28-day cycle, this places ovulation at day 14 and conception at day 14, giving a 266-day gestation from conception. If your cycle length differs, our calculator automatically adjusts the EDD accordingly.
✏️ Last updated: — All formulas verified against WHO & NIH clinical guidelines.
Frequently Asked Questions
Long-tail answers to the most searched health calculator questions worldwide
What is a healthy BMI for adults in the UK, USA, and Australia?
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According to the WHO, a healthy BMI for adults 20+ is 18.5–24.9. Underweight is below 18.5, overweight is 25–29.9, and obese is 30+. These thresholds apply universally for adults. Note that some Asian populations use lower cut-offs (23 for overweight, 27.5 for obese) due to different fat distribution patterns. For personalised guidance, consult your GP or physician.
How many calories per day to lose weight for women and men?
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For safe, sustainable weight loss: eat 500–750 kcal below your TDEE. This creates a weekly deficit of 3,500–5,250 kcal = 0.5–0.75 kg of fat loss per week. Women typically need 1,600–2,400 kcal/day; men 2,000–3,000 kcal/day depending on activity. Use our Calorie Calculator above to get your exact personal TDEE first — then subtract your deficit from that number.
What is a normal body fat percentage for men and women by age?
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Per the American Council on Exercise: Essential fat: 2–5% (men), 10–13% (women). Athlete: 6–13% (men), 14–20% (women). Fitness: 14–17% (men), 21–24% (women). Average: 18–24% (men), 25–31% (women). Obese: 25%+ (men), 32%+ (women). Body fat naturally increases with age, so optimal ranges shift slightly upward past age 40. Our Body Fat Calculator flags which category you fall into.
Is the BMI calculator accurate for athletes and muscular people?
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BMI does not distinguish between muscle and fat mass, so heavily muscled athletes can show "overweight" or "obese" BMI despite low body fat. For example, an NFL linebacker weighing 120 kg at 185 cm has a BMI of 35 — technically obese — but may have only 12% body fat. If you are athletic, use our Body Fat Calculator alongside BMI for a more accurate assessment of your body composition.
How accurate is the pregnancy due date calculator?
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Naegele's Rule is accurate within ±2 weeks for the majority of pregnancies. Only about 5% of babies arrive on their exact EDD. Early ultrasound (before 12 weeks) can refine the due date to within 5–7 days, which is why your obstetrician may adjust the EDD after your dating scan. Our calculator gives an excellent estimate for planning, but always confirm with your healthcare provider.
What is the recommended daily water intake for weight loss?
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Studies show drinking 500 ml of water 30 minutes before each meal can increase metabolic rate by 24–30% for 60–90 minutes and reduce meal-time calorie intake by 13%. The US National Academies recommends 3.7 litres/day (men) and 2.7 litres/day (women) total water from all sources (food + beverages). In hot climates or during exercise, add 0.5–1 litre per hour of activity.
Can I use these calculators during pregnancy for nutrition planning?
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Our Calorie and Water calculators can provide a useful baseline during pregnancy. Calorie needs increase by approximately 300–500 kcal/day in the second and third trimesters. Water needs increase by 300–500 ml/day. However, pregnancy nutrition is highly individual — always consult your midwife, OB-GYN, or registered dietitian before making significant dietary changes during pregnancy.
Are these health calculators suitable for children and teenagers?
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All calculators on this page are validated for adults aged 18 and over. BMI for children uses age- and sex-specific percentile charts (not fixed cut-offs), because children's body composition changes rapidly with growth. For ages 2–19, the CDC's child BMI calculator or your paediatrician's growth chart is the appropriate tool. Our adult BMI, calorie, and body fat calculators should not be used for minors.