BMR CALCULATOR

Free BMR Calculator
Calculate Basal Metabolic Rate

Three clinically-validated formulas. Instant calorie results. The first step toward smarter weight loss.

✓ Mifflin-St Jeor ✓ Harris-Benedict ✓ Katch-McArdle ✓ Imperial & Metric

Enter Your Details

Please enter a valid age (15–100).
Enter feet (3–8).
Enter inches (0–11).
Enter weight in lbs (50–700).
Enter body fat % (3–70).

Your BMR Results

ℹ️ BMR = calories burned at complete rest. Multiply by your activity level (see sidebar) to find your TDEE.

What Is a BMR Calculator?

A BMR calculator estimates the number of calories your body burns every day just to stay alive — no movement required. BMR stands for Basal Metabolic Rate, and it represents the energy your organs (brain, heart, liver, kidneys) consume at complete rest. Think of it as the "idle speed" of your metabolism.

Knowing how to calculate basal metabolic rate is the essential first step before setting any calorie target, whether your goal is weight loss, muscle gain, or simply maintaining a healthy body.

Why Your BMR Matters for Weight Loss

Your BMR sets the floor for how many calories you need. Eat fewer than your BMR for extended periods and your body enters a survival mode — muscle breaks down, metabolism slows, and long-term fat loss stalls. Eating slightly below your Total Daily Energy Expenditure (TDEE = BMR × activity factor) creates a safe, sustainable calorie deficit.

The standard evidence-based recommendation is a 300–500 kcal/day deficit, which translates to roughly 0.3–0.5 kg of fat loss per week — enough to produce real results without triggering metabolic adaptation.

Ready to find your full calorie target?

Use our TDEE calculator to include your activity level and get your complete daily calorie goal.

Calculate My TDEE →

The Three BMR Formulas Explained

1. Mifflin-St Jeor Equation (Recommended)

Developed in 1990, the Mifflin-St Jeor equation is the most widely validated formula for the general adult population. Multiple peer-reviewed studies confirm it outperforms the original Harris-Benedict equation in predicting resting energy expenditure.

Men: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

2. Harris-Benedict Equation (Revised 1984)

Originally published in 1919 and revised by Roza and Shizgal in 1984, the Harris-Benedict formula remains a robust reference. The revised version corrects for the slight over-prediction of the original and is still used in many clinical settings.

Men: BMR = (13.397 × kg) + (4.799 × cm) − (5.677 × age) + 88.362
Women: BMR = (9.247 × kg) + (3.098 × cm) − (4.330 × age) + 447.593

3. Katch-McArdle Equation

The Katch-McArdle formula is unique because it uses lean body mass rather than total body weight. This makes it the most accurate option for people who know their body-fat percentage — particularly athletes, bodybuilders, or anyone who has recently had a DEXA scan or body-composition test.

Lean Body Mass (LBM): LBM = weight in kg × (1 − body fat % ÷ 100)
BMR: 370 + (21.6 × LBM in kg)

How to Use the BMR Calculator: Step-by-Step

Step 1. Choose your unit system (Imperial or Metric).

Step 2. Select your biological sex — BMR differs significantly between males and females due to differences in muscle mass and hormones.

Step 3. Enter your age, height, and weight accurately. Even small errors in weight can shift results by 30–50 kcal.

Step 4. If you know your body-fat percentage, tick Katch-McArdle and enter it for a more personalised result.

Step 5. Click Calculate My BMR and compare results across all selected formulas.

Step 6. Multiply your BMR by the activity multiplier (see sidebar) to get your full TDEE — your real daily calorie target.

Frequently Asked Questions

What is a normal BMR for a woman? ▼
For most adult women, BMR falls between 1,200 and 1,800 kcal/day. The exact number depends on age, height, weight, and muscle mass. A 30-year-old woman at 165 cm and 65 kg will typically have a Mifflin-St Jeor BMR of approximately 1,430 kcal.
What is a normal BMR for a man? ▼
Most adult men have a BMR between 1,600 and 2,200 kcal/day. A 35-year-old man at 180 cm and 80 kg has a Mifflin-St Jeor BMR of roughly 1,854 kcal. Higher muscle mass drives a higher BMR.
Does BMR change as you age? ▼
Yes. BMR declines gradually with age — roughly 1–2% per decade after age 20, primarily because lean muscle mass decreases (sarcopenia). This is why resistance training becomes increasingly important after 30, as preserving muscle mass keeps metabolic rate higher.
Can I increase my basal metabolic rate? ▼
Yes. The most effective ways are: (1) building lean muscle through resistance training — each kg of muscle burns ~13 kcal/day at rest; (2) eating enough protein (1.6–2.2 g/kg) to prevent muscle loss during a cut; (3) avoiding extreme calorie restriction, which signals the body to down-regulate metabolism.
Is BMR the same as RMR? ▼
Nearly — but not exactly. BMR (Basal Metabolic Rate) is measured under strict clinical conditions (complete rest, fasted, thermoneutral environment). RMR (Resting Metabolic Rate) is measured at rest but without those strict conditions, so it's slightly higher (by ~10–15%). For practical calorie tracking, the difference is negligible and the terms are often used interchangeably.
How accurate are online BMR calculators? ▼
Predictive equations like Mifflin-St Jeor are accurate to within ±10% for most people. The Katch-McArdle formula reduces error further for lean individuals. Use your BMR result as a starting estimate, then track your actual weight for 2–3 weeks and adjust calories up or down based on real results.

BMR vs TDEE: What's the Difference?

BMR is what you burn doing nothing. TDEE (Total Daily Energy Expenditure) is what you actually burn in a real day — it adds the calories from walking, exercise, digestion (the thermic effect of food), and non-exercise activity thermogenesis (NEAT) like fidgeting, standing, and daily chores.

For most people, TDEE is 20–60% higher than BMR. A sedentary office worker multiplies their BMR by 1.2; a construction worker or serious athlete might multiply by 1.7–1.9. This is why two people of the same height and weight can have very different calorie needs.