BMR Calculator

What the BMR Calculator does

Basal metabolic rate is the energy your body uses at complete rest to run your heart, brain, lungs and cell repair. It accounts for roughly 60–70% of total daily calorie burn, which is why it is the foundation of any nutrition plan.

Formula

• Mifflin-St Jeor (male): 10×kg + 6.25×cm − 5×age + 5
• Mifflin-St Jeor (female): 10×kg + 6.25×cm − 5×age − 161
• Katch-McArdle: 370 + 21.6 × lean body mass (kg)

Inputs explained

How to use it

1. Choose Units and Sex.
2. Enter Weight, Height and Age.
3. Fill in the remaining inputs the form shows for your choice.
4. Select Calculate.

Worked example

A 30-year-old man, 80 kg, 180 cm.

Weight

80 kg

Height

180 cm

Age

30

Sex

Male

10(80) + 6.25(180) − 5(30) + 5 = 1,780 calories a day at rest.

Reading the result

• BMR is the energy your body uses at complete rest to run circulation, breathing and cell repair. It is a floor, not a daily calorie target.
• Your actual daily need is BMR multiplied by an activity factor — that figure is what the TDEE calculator produces.
• Eating at or below BMR for extended periods is not a faster route to weight loss; it tends to cost lean tissue.

Assumptions and limitations

• Every BMR equation is a population regression. Individual metabolic rate varies by roughly 10% either side of the prediction even when height, weight, age and sex all match.
• Mifflin-St Jeor is the modern default and is generally the most accurate for the general population. Harris-Benedict runs slightly high; Katch-McArdle is usually better if you have a reliable body-fat figure, because it works from lean mass.
• None of the equations account for thyroid conditions, medication, or metabolic adaptation after prolonged dieting.

Common mistakes

• Confusing BMR with TDEE and eating hundreds of calories below what the day actually requires.
• Using Katch-McArdle with a guessed body-fat percentage — a wrong lean-mass figure makes it less accurate than the simpler equations, not more.
• Recalculating only after large weight changes. BMR falls as weight falls, so a target set months ago drifts out of date.

Frequently asked questions

Which formula should I use?

Mifflin-St Jeor is the most accurate for the general population. If you know your body fat percentage reliably, Katch-McArdle is better because it works from lean mass.

Can I increase my BMR?

Building muscle helps, since lean tissue burns more at rest than fat. The effect is real but modest — roughly 13 calories per kg of muscle per day.

Method and sources

Method. Three published predictive equations, selected by the reader: Mifflin-St Jeor (the default), the Roza and Shizgal revision of Harris-Benedict, and Katch-McArdle, which predicts from lean body mass instead of height and age.

Assumptions

• The reader is a healthy non-pregnant adult. All three equations were derived from adult populations and none is validated for children.
• Katch-McArdle needs a body-fat percentage the reader supplies; its accuracy is bounded by how that figure was measured.

Limitations

• These are population regressions, not measurements. Individual resting expenditure commonly differs from the prediction by around ten per cent in either direction, and more at the extremes of body size.
• None of the equations accounts for thyroid function, medication, illness or recent dieting, all of which move resting metabolic rate.
• The three equations disagree with each other by design; comparing a figure from one against a target derived from another is not meaningful.

Sources

• A new predictive equation for resting energy expenditure in healthy individuals — The American Journal of Clinical Nutrition, 1990. The Mifflin-St Jeor coefficients (10 × kg, 6.25 × cm, −5 × age, +5 / −161).
• The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass — The American Journal of Clinical Nutrition, 1984. The revised Harris-Benedict coefficients (88.362 / 447.593 constants and their multipliers).
• Exercise Physiology: Nutrition, Energy, and Human Performance — Katch, McArdle and Katch (Lippincott Williams & Wilkins). The Katch-McArdle form, BMR = 370 + 21.6 × lean body mass in kilograms.

Related calculators

• TDEE Calculator
• Calorie Calculator
• Macro Calculator
• BMI Calculator