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BMR Calculator

Calculate your Basal Metabolic Rate — the calories your body burns at complete rest.

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Enter your details to see your BMR

Basal Metabolic Rate — the calories your body burns at complete rest. Roughly 60–70% of your total daily burn.

How to use this calculator

  1. 1

    Pick your units

    Imperial (lb / ft / in) or metric (kg / cm). The form swaps over instantly.

  2. 2

    Fill in your stats

    Enter your sex, age, weight, and height. These are all the formula needs to estimate your at-rest calorie burn.

  3. 3

    Optional: add body fat %

    If you know your body fat %, enter it for a more accurate estimate — the calculation can use your lean body mass directly via the Katch-McArdle formula.

  4. 4

    Read your results

    Your BMR appears with a ±5% honest range. Compare across all four supported formulas to see how different equations agree.

What is BMR?

Your Basal Metabolic Rate is the number of calories your body burns when you're completely at rest — lying still, awake, not digesting food, in a thermally neutral environment.

BMR is what your body needs just to keep the lights on: breathing, blood circulation, brain function, cellular maintenance. For most people it accounts for 60–70% of total daily calorie burn.

What affects BMR

  • Body size — bigger bodies burn more (more cells to maintain)
  • Lean mass — muscle is metabolically active; fat is mostly not. Two people of the same weight can have meaningfully different BMRs if body composition differs.
  • Age — BMR drops about 1–2% per decade after 30
  • Sex — males typically have higher BMR per kg due to higher average lean mass
  • Genetics — there's a ~15–25% inter-individual variance even among people with identical measurable inputs
  • Thyroid function — hyper/hypothyroidism shifts BMR significantly
  • Diet history — sustained calorie restriction can suppress BMR via adaptive thermogenesis

How is BMR calculated?

Several equations exist for estimating BMR. They take different inputs and were validated on different populations — which is why our calculator supports four of them.

Mifflin-St Jeor (1990) — default

The current standard recommended by the Academy of Nutrition and Dietetics. In published meta-analyses it's generally validated as among the most accurate predictors for the general adult population (ages 19–78).

Men: BMR = 10W + 6.25H − 5A + 5

Women: BMR = 10W + 6.25H − 5A − 161

W = weight (kg), H = height (cm), A = age

Note: the female constant is −161, per the original 1990 paper.

Katch-McArdle (1996) — generally most accurate when body fat is known

Uses lean body mass directly. Generally the most accurate option when you have a reliable body composition measurement, because it skips the indirect proxy of weight + height + sex.

BMR = 370 + 21.6 × LBM

LBM = lean body mass (kg) = weight × (1 − bodyfat%)

Henry / Oxford (2005) and Revised Harris-Benedict (1984)

Two alternatives available under Advanced options. Henry/Oxford is derived from a larger and more diverse dataset than Mifflin's original; Revised Harris-Benedict is the classic equation still widely used. Both produce results within a few percent of Mifflin in most cases.

How accurate is the result?

Mifflin-St Jeor predicts BMR within ±10% of indirect-calorimetry measurements in roughly 82% of non-obese and 70% of obese adults. We display a ±5% range as a conservative honest interval; individual variance can be wider.

Factors not captured by the equation include thyroid status, certain medications (beta-blockers lower BMR ~5–10%), pregnancy/lactation, and recent weight-loss history.

In practice

BMR is your body's baseline calorie burn at rest — it's the foundation, not the full picture. To estimate your total daily calorie burn including activity, use the TDEE calculator.

Frequently asked questions

Sources & references

Studies, equations, and clinical guidance behind the calculations.

  • Mifflin-St Jeor (1990). Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr 51(2):241–7. PubMed
  • Henry / Oxford (2005). Henry CJK. Basal metabolic rate studies in humans: measurement and development of new equations. Public Health Nutr 8(7A):1133–52. PubMed
  • Revised Harris-Benedict (1984). Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr 40(1):168–82. PubMed
  • Katch-McArdle (1996). McArdle WD, Katch FI, Katch VL. Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins. (Textbook — no online link.)
  • Academy of Nutrition and Dietetics. Adult Weight Management Evidence-Based Nutrition Practice Guideline. EAL Guideline

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