Calorie Calculator

What Is Your BMR? Find Out With Our Free BMR Calculator

Have you ever wondered exactly how many calories your body needs just to function at rest? This number is your Basal Metabolic Rate, or BMR, and understanding it is a powerful first step in achieving your health and fitness goals. Whether you're looking to manage your weight, build muscle, or simply live a healthier life, knowing your BMR helps you create a personalized plan that really works. Ready to find yours? Use our simple, trusted BMR calculator below to get your personalized results in seconds and start your journey with confidence.

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Tell Us About Yourself

Units

We’ll only use the fields that match the selected unit system.

Basic Information
Activity Level (for TDEE)

We multiply your BMR by this factor to estimate TDEE.

Height & Weight

Prefer one system? Fill only that set. We’ll ignore the other.

Optional / Advanced

We calculate BMR via Mifflin–St Jeor by default. If you provide body-fat %, we use Katch–McArdle. TDEE = BMR × activity factor. Estimates only—not medical advice.

Understanding Your BMR (Basal Metabolic Rate)

Basal Metabolic Rate (BMR) is one of the most important numbers in nutrition and fitness. It’s the baseline energy your body needs every day to keep you alive—before workouts, steps, chores, and everything else. Whether your goal is fat loss, muscle gain, or maintenance, understanding BMR gives you the foundation for setting realistic calorie targets that work in the real world.

On this page you’ll find a complete, friendly walkthrough of what BMR is, how we calculate it, how it relates to TDEE (Total Daily Energy Expenditure), and how to use your results to eat and train with confidence.

BMR Calculator Tool

The calculator above uses research-backed equations to estimate your daily energy needs at rest. For most people, we default to Mifflin–St Jeor due to its strong accuracy in modern populations. If you provide body-fat percentage, we can use Katch–McArdle to personalize the estimate based on lean mass.

Inputs: age, sex, height, weight, and activity level (to estimate TDEE). Optional: body-fat %.

Outputs: BMR, TDEE, and suggested calorie targets for maintenance, weight loss, and muscle gain.

How to Use the BMR Calculator

  1. Select your preferred units (U.S. or metric).
  2. Enter age, sex, height, and weight carefully for best accuracy.
  3. Pick your activity level (sedentary to very active) to estimate TDEE.
  4. Optional: add body-fat % if you know it to enable Katch–McArdle.
  5. Press Calculate to see BMR, TDEE, and daily calorie targets.

Example: A moderately active 35-year-old woman at 5′6″ and 150 lb might see ~1,420 cal/day BMR and ~2,200 cal/day TDEE, with a weight-loss target near ~1,700 cal/day (a ~500-cal deficit).

Understanding Your Results

You’ll see two key numbers—BMR (calories at rest) and TDEE (your total daily burn including activity)—plus suggested intakes for maintenance, a healthy deficit, or a lean bulk.

BMR vs. TDEE (Total Daily Energy Expenditure)

MetricMeaningWhat It Represents
BMRBasal Metabolic RateCalories your body uses at complete rest to sustain life
TDEETotal Daily Energy ExpenditureBMR multiplied by an activity factor; includes daily movement and exercise

If you want to maintain weight, aim near your TDEE. For fat loss, eat fewer calories than TDEE. For muscle gain, add a modest surplus above TDEE.

Calculating Your Daily Calorie Needs

  • Maintenance: Eat approximately your TDEE.
  • Weight Loss: TDEE minus 250–500 calories/day (about 0.5–1.0 lb/week).
  • Muscle Gain: TDEE plus 250–500 calories/day (lean, sustainable surplus).

Quick tip: Extreme deficits often backfire. Smaller, sustainable changes preserve energy, training quality, and lean mass—especially when combined with adequate protein and resistance training.

Factors That Influence BMR

BMR isn’t static—it responds to your biology, habits, and environment. Here are the biggest drivers:

  • Age: BMR tends to decline with age, largely due to lean-mass loss and hormonal changes.
  • Sex: Men generally have higher BMRs than women due to more lean mass.
  • Body Composition: Muscle is metabolically active—more lean mass usually means higher BMR.
  • Genetics: Some people naturally run “hotter” or “cooler,” metabolically speaking.
  • Hormones: Thyroid function (T3, T4), cortisol, and sex hormones affect metabolic rate.
  • Environment: Cold exposure, altitude, and chronic stress can nudge metabolism up or down.
  • Diet Composition: Protein has a higher thermic effect; adequate protein supports lean mass.

Common BMR Formulas Explained

All BMR equations consider height, weight, age, and sex—but they weigh those factors differently. Below are the three most cited approaches, with a quick note on when each shines.

Mifflin–St Jeor Equation

Often the best choice for most adults today.

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

Developed in the 1990s and validated in modern cohorts, Mifflin–St Jeor typically tracks reality better than older formulas for the general population.

Harris–Benedict Equation

A classic formula that may slightly overestimate for some people.

Men:    BMR = 66.5 + 13.75 × weight(kg) + 5.003 × height(cm) − 6.755 × age
Women:  BMR = 655.1 + 9.563 × weight(kg) + 1.850 × height(cm) − 4.676 × age

Still widely used for historical continuity. Good for comparison, but many users will prefer Mifflin–St Jeor.

Katch–McArdle Equation

Ideal if you know your body-fat percentage.

BMR = 370 + (21.6 × Lean Body Mass in kg)
LBM = Weight(kg) × (1 − Body Fat % / 100)

Because it’s based on lean mass, Katch–McArdle can be very accurate for athletes or anyone who tracks body composition closely.

How to Increase Your BMR

  • Build and keep lean muscle: Prioritize resistance training 2–4×/week.
  • Move more across the day: NEAT (steps, standing, fidgeting) meaningfully raises daily burn.
  • Eat enough protein: Aim for ~1.6–2.2 g/kg body weight if you train; protein also boosts TEF.
  • Sleep well: Poor sleep disrupts appetite and thyroid-related hormones.
  • Manage stress: Chronically high cortisol can suppress thyroid activity and training quality.
  • Hydrate: Dehydration can reduce metabolic efficiency and performance.
  • Avoid extreme deficits: Prolonged very-low-calorie diets can depress metabolic rate over time.

Limitations of BMR Calculators

Online tools are estimates, not diagnoses. Expect a typical margin of error around 5–10% from lab-grade measurements. Real-world outcomes also depend on tracking accuracy, food choices, sleep, stress, and training consistency. Treat your BMR and TDEE as a smart starting point, then adjust intake based on your trend over several weeks.

Frequently Asked Questions

How accurate is this BMR calculator?

Quite accurate for most adults, especially using Mifflin–St Jeor or Katch–McArdle with reliable body-fat data. Plan on a practical error band of 5–10% and fine-tune based on your progress.

Should I eat my exact BMR to lose weight?

No. BMR is your resting requirement. Use your TDEE (BMR × activity) and create a moderate deficit below that—typically 250–500 calories/day for steady, sustainable fat loss.

What’s the difference between BMR and RMR?

BMR is measured under strict lab conditions. RMR (Resting Metabolic Rate) is more practical and slightly higher, reflecting a relaxed waking state. The terms are often used interchangeably outside research.

How often should I recalculate?

Re-check whenever your body weight changes by 5–10%, your training volume shifts meaningfully, or your job/lifestyle activity changes.

What if I have a thyroid issue?

Talk to your healthcare provider. Calculators can’t diagnose or adjust for clinical conditions. If your outcomes don’t line up with expectations despite careful tracking, medical guidance is the best next step.

Helpful Next Steps