Health Calculators
Free BMI, calorie, body fat, and fitness calculators. Track your health metrics with accurate, science-based tools.
Health Calculators - Know Your Numbers, Own Your Wellbeing
Understanding your health starts with measurement. Body weight, calorie needs, heart rate zones, hydration targets - these numbers guide every effective fitness and nutrition plan. NeutronDB’s health calculators use clinically validated formulae (WHO BMI standards, Mifflin–St Jeor BMR equation, Karvonen heart-rate formula) so you can trust the results, not just guess at them.
Three Focused Subcategories
Understanding the Key Metrics
BMI (Body Mass Index) is the most widely used screening tool for healthy weight. Calculated as weight (kg) ÷ height (m)², it classifies adults into underweight, normal, overweight, and obese ranges per WHO guidelines. Use it alongside Body Fat % for a more complete picture.
BMR (Basal Metabolic Rate) is the calories your body burns at complete rest. Multiply by an activity factor to get TDEE - the true number of calories you need per day - then feed that into the Calorie Deficit Calculator for a safe, sustainable fat-loss target.
Heart Rate Zones are calculated as percentages of your maximum heart rate. Zone 2 (60–70%) builds aerobic base; Zone 4 (80–90%) improves lactate threshold. The Running Pace Calculator then helps you translate that zone into a target min/km pace for any race distance.
The Three-Step Health Planning Sequence
Start with the BMI Calculator and BMR Calculator to establish your baseline. Then use the Macro Calculator to plan what to eat. Finally use the Calories Burned Calculator and Heart Rate Zone Calculator to plan how to train.
Frequently Asked Questions
Which BMI calculator formula do you use?
We use the standard WHO formula: BMI = weight (kg) ÷ height (m)². For imperial inputs, BMI = (weight in lb ÷ height in inches²) × 703. See the full breakdown on the BMI Calculator page.
What is the difference between BMR and TDEE?
BMR (Basal Metabolic Rate) is calories burned at complete rest. TDEE multiplies BMR by an activity factor (1.2 for sedentary to 1.9 for very active). TDEE is what you use for practical meal planning - calculate it with the BMR Calculator.
How accurate is the body fat calculator?
The Body Fat Calculator uses the US Navy circumference method, accurate to ±3–4% vs. DEXA scans. It is a practical estimate for tracking trends over time.
What calorie deficit is safe for weight loss?
A deficit of 300–500 kcal per day from TDEE leads to approximately 0.3–0.5 kg of fat loss per week - considered safe and sustainable. The Calorie Deficit Calculator enforces a minimum intake floor to prevent muscle loss.