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BMR Calculator

Calculate your Basal Metabolic Rate — the calories your body burns at complete rest — using the Mifflin-St Jeor formula, with a Harris-Benedict comparison, in metric or imperial units.

Understanding the BMR Calculator

The BMR Calculator estimates your Basal Metabolic Rate — the number of calories your body burns at complete rest just to stay alive, powering your brain, heart, lungs, and other organs. BMR usually makes up 60–70% of the total calories you burn each day, making it the foundation of any calorie or weight-management plan. Enter your sex, age, height, and weight in metric or imperial units, and the tool returns your resting calories using the Mifflin-St Jeor equation, the formula most clinicians and dietitians consider the most accurate for the general population. It also shows the revised Harris-Benedict result so you can compare both widely used methods at a glance.

How it works

You choose your sex and units, then enter age, weight, and height. The calculator converts imperial inputs to metric (pounds to kilograms, feet and inches to centimetres) and applies the Mifflin-St Jeor equation: for men, BMR = 10×kg + 6.25×cm − 5×age + 5; for women the constant is −161 instead of +5. It also computes the revised Harris-Benedict estimate for comparison. The result is your resting calorie burn per day. Because BMR ignores movement, it is only the starting point — multiplying it by an activity factor gives your TDEE (Total Daily Energy Expenditure), the calories you actually burn. Inputs are validated gently (age 14–100, positive height and weight) and nothing is sent to a server.

Mifflin-St Jeor (primary): Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161 Harris-Benedict, revised (shown for comparison): Men: BMR = 88.362 + 13.397 × weight(kg) + 4.799 × height(cm) − 5.677 × age Women: BMR = 447.593 + 9.247 × weight(kg) + 3.098 × height(cm) − 4.330 × age Then: TDEE = BMR × activity factor (1.2 sedentary to 1.9 extra active).

Worked example

A 30-year-old woman who is 165 cm tall and weighs 65 kg gets: BMR = 10×65 + 6.25×165 − 5×30 − 161 = 650 + 1031.25 − 150 − 161 ≈ 1,370 calories per day at rest. If she is moderately active (factor 1.55), her TDEE is about 1,370 × 1.55 ≈ 2,124 calories per day to maintain her weight.

Tips & common mistakes

  • BMR is your resting baseline only — multiply it by an activity factor (use the TDEE calculator) to estimate the calories you actually burn in a day.
  • Mifflin-St Jeor is generally the most accurate for most adults; treat the Harris-Benedict figure as a sanity check, not a second opinion.
  • Measure weight in the morning before eating for a consistent input, and re-run the numbers whenever your weight changes by a few kilograms.
  • BMR naturally declines with age and is lower with less muscle mass — strength training that builds muscle can modestly raise it.
  • These equations don't account for body composition, so very muscular or very lean people may see less accurate estimates.
  • Use BMR as a planning guide, not a target — never eat below your BMR for long without guidance from a doctor or dietitian.

Sources & methodology

  • • Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition, 1990.
  • • Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. American Journal of Clinical Nutrition, 1984.

Related tools

TDEE CalculatorCalculate your daily calorie needs (TDEE) and BMR from age, weight, height, and activity.Macro CalculatorSplit your daily calories into protein, carbs, and fat for your goal.BMI CalculatorCalculate your Body Mass Index from height and weight, with your healthy-weight range — metric or imperial.Body Fat CalculatorEstimate your body fat percentage using the U.S. Navy method from a few body measurements.

Reviewed by the TopOpenTools editorial team · Last updated June 2026. These tools provide general estimates for educational purposes only and are not financial, tax, insurance, investment, or medical advice. Verify important decisions with a qualified professional.

How to Use This Calculator

  1. 1Choose your sex and units, then enter your age, weight, and height.
  2. 2Click Calculate BMR to see your resting calories from both formulas.
  3. 3Multiply by your activity level with the TDEE calculator to get your full daily calorie needs.

Frequently Asked Questions

What is BMR?

BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest just to stay alive — powering your brain, heart, lungs, and other organs. It typically accounts for 60–70% of the calories you burn each day.

Which formula is used?

This calculator uses the Mifflin-St Jeor equation as its primary estimate, which is widely regarded as one of the most accurate for the general population. It also shows the revised Harris-Benedict result so you can compare the two.

How is BMR different from TDEE?

BMR is the calories you burn at rest. TDEE (Total Daily Energy Expenditure) is your BMR multiplied by an activity factor that accounts for movement and exercise — so TDEE = BMR × your activity level.