Basal Metabolic Rate (BMR) is the energy your body expends at complete rest to sustain vital functions like breathing and circulation.

Which BMR formula is best?

Mifflin–St Jeor is widely used today; Harris–Benedict (revised) is a classic reference; Katch–McArdle is great if you know your body-fat% because it uses lean mass.

How do I turn BMR into daily calories?

Multiply BMR by an activity factor (1.2–1.9) to estimate TDEE, then adjust calories up or down for your goal.

No, but if you have a reliable estimate, Katch–McArdle can personalize BMR using lean mass. Otherwise use Mifflin–St Jeor or Harris–Benedict.

BMR Calculator — Mifflin–St Jeor, Harris–Benedict (Revised) & Katch

BMR Calculator Guide: How It Works, Which Formula to Pick, and How to Use It

Table of Contents

What is BMR? How is it different from RMR?
The big three formulas (MSJ, HB-Revised, KMA)
Choosing the right formula for you
From BMR to TDEE: activity factors
How to use BMR/TDEE for goals
Accuracy tips & limitations
FAQs

1) What is BMR? How is it different from RMR?

Basal Metabolic Rate (BMR) is the energy your body uses at complete rest under very strict lab conditions. Resting Metabolic Rate (RMR) is similar but less strict, usually measured after waking, before food, in a calm setting. In practice, many online calculators use the terms interchangeably; just use one method consistently.

2) The big three formulas (MSJ, HB-Revised, KMA)

Mifflin–St Jeor (MSJ): modern, widely used. Men: 10×kg + 6.25×cm − 5×age + 5. Women: 10×kg + 6.25×cm − 5×age − 161.

Harris–Benedict (Revised): an updated version of an early 20th‑century equation—still popular for reference. Men: 88.362 + 13.397×kg + 4.799×cm − 5.677×age. Women: 447.593 + 9.247×kg + 3.098×cm − 4.330×age.

Katch–McArdle (KMA): 370 + 21.6 × LBM(kg). It needs body‑fat% to estimate lean body mass (LBM). Great if your BF% is measured fairly well.

3) Choosing the right formula for you

No body‑fat%? Start with MSJ (default) or HB (revised). They use height, weight, age, and sex.
Have a reliable BF%? Try KMA—it personalizes BMR using lean mass and can be more relevant for athletes.
Muscular/atypical body types: Cross‑check with KMA or a professional assessment.

4) From BMR to TDEE: activity factors

To estimate daily calories, multiply BMR by an activity factor (1.2–1.9). Sedentary ~1.2, Light ~1.375, Moderate ~1.55, Active ~1.725, Very Active ~1.9. This yields TDEE—then set a modest deficit/surplus for fat loss or muscle gain.

5) How to use BMR/TDEE for goals

After estimating TDEE, adjust calories by ~10–20% to lose or gain weight gradually. Track weekly averages (weight, measurements, progress photos, gym performance), and tweak calories/macros as needed.

6) Accuracy tips & limitations

These are estimates, not diagnoses. Real‑world results matter—measure and adjust.
Body‑fat% inputs can shift results; use consistent methods (DEXA, calipers, or a trusted device) at the same time of day.
Health conditions, medications, and genetics affect metabolism—work with a professional when needed.

7) FAQs

Why does my BMR seem “too low” or “too high”?

Different equations and inputs produce different values. Compare estimates, pick one approach, and calibrate with your weekly progress.

Is BMR the calories I should eat?

No—BMR is your resting energy use. For daily intake, estimate TDEE by applying an activity multiplier, then adjust for your goal.

How often should I recalculate?

Anytime weight changes by ~2–5%, or your activity pattern changes for a few weeks.

Disclaimer: Informational purposes only—always consult your healthcare provider or a registered dietitian for personalized guidance.

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