BMI Calculator
BMI (Body Mass Index) measures body fat based on height and weight. A healthy BMI is 18.5–24.9. This calculator goes beyond simple BMI — it also computes your healthy weight range, ideal body weight, BMR (calories at rest), and TDEE (total daily calories needed) for weight loss, maintenance, or gain.
How BMI and Calorie Needs Are Calculated
BMI uses height and weight to estimate whether a person is at a healthy weight. While imperfect (it doesn't account for muscle mass), it's the standard screening tool used by physicians worldwide. This calculator uses the Mifflin-St Jeor equation for BMR — the most validated formula for estimating resting calorie needs.
| Variable | Definition |
|---|---|
| BMI | Body Mass Index — weight-to-height ratio screening tool |
| BMR | Basal Metabolic Rate — calories burned completely at rest |
| TDEE | Total Daily Energy Expenditure — BMR × activity multiplier |
| W, H, A | Weight (kg), Height (cm), Age (years) in Mifflin-St Jeor equation |
| IBW | Ideal Body Weight using Devine formula (adjusted per inch over 5ft) |
Worked example: Male, age 35, 5'10", 185 lbs (83.9 kg, 177.8 cm). BMI = 83.9 ÷ (1.778)² = 83.9 ÷ 3.16 = 26.5 (Overweight). Healthy range: 128–173 lbs. BMR = (10×83.9) + (6.25×177.8) − (5×35) + 5 = 839 + 1,111 − 175 + 5 = 1,780 cal/day. At moderate activity (TDEE multiplier 1.55): TDEE = 1,780 × 1.55 = 2,759 cal/day to maintain weight. To lose 1 lb/week: 2,259 cal/day.
💪 Health Expert Insight
BMI Has Real Limitations — Here's What Actually Predicts Health Risk: A 200 lb bodybuilder and a 200 lb sedentary person have the same BMI — but dramatically different health profiles. The better metrics: waist-to-height ratio (waist circumference ÷ height, healthy = below 0.5), body fat percentage (men: 10–20% healthy; women: 18–28%), and waist circumference alone (under 35 inches for women, 40 inches for men). That said, BMI remains useful as a population-level screening tool and correlates well with health outcomes at the extremes. Use BMI as one data point, not the whole story.
BMI Calculator FAQ
What is a healthy BMI range?
A healthy BMI falls between 18.5 and 24.9. Below 18.5 is underweight. 25.0–29.9 is overweight. 30.0 and above is obese (Class I: 30–34.9, Class II: 35–39.9, Class III: 40+).
How is BMI calculated?
BMI = weight (kg) ÷ height² (m²). In imperial: BMI = (weight in lbs × 703) ÷ height in inches². A person who is 5'10" and weighs 185 lbs: BMI = (185 × 703) ÷ 4,900 = 26.5.
What is TDEE and why does it matter for weight loss?
TDEE (Total Daily Energy Expenditure) is the total calories your body burns daily. Eat below TDEE to lose weight, above to gain. A 500 calorie/day deficit below TDEE produces ~1 lb/week weight loss. Never go below 1,200 calories/day without medical supervision.
What are the limitations of BMI?
BMI doesn't distinguish muscle from fat — athletes often have high BMI but low body fat. It doesn't account for fat distribution. Waist circumference and body fat percentage are often more clinically meaningful for individual health assessment.
How accurate is the Mifflin-St Jeor equation?
The Mifflin-St Jeor equation is considered the most accurate BMR formula for most adults, validated in multiple clinical studies. It's accurate within ±10% for most people. The actual TDEE varies based on your true activity level — the activity multipliers are estimates. Track calories for 2–3 weeks and adjust based on actual weight change.
BMI Calculator + TDEE & Calorie Needs
Your Measurements
Your Results
Based on your results — what to do next:
Set a health-related savings goal
Gym memberships, meal prep, and fitness gear add up. Use the savings goal calculator to budget for your health goals alongside your BMI target.
Check your take-home pay
Health and wellness expenses can be tax-deductible. See your net take-home to know what's available for fitness investments.
Track your financial health too
Physical and financial health go hand in hand. Know your full financial picture alongside your BMI progress.