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Free online BMR calculator

BMR (basal metabolic rate) is the calories your body burns just to stay alive at rest. This calculator estimates yours from age, sex, height, and weight.

Units
BMR (Mifflin-St Jeor)
—
kcal / day
About this calculator

How to use

  1. Choose Imperial or Metric with the toggle.
  2. Select a formula from the dropdown — Mifflin-St Jeor is the default.
  3. Enter sex, age, weight, and height. If using Katch-McArdle, also enter body fat %.
  4. Your BMR in kcal/day appears, labeled with the formula used.

The three formulas

Mifflin-St Jeor (1990) — recommended:

Men:   10W + 6.25H − 5A + 5
Women: 10W + 6.25H − 5A − 161

Harris-Benedict revised (Roza & Shizgal, 1984):

Men:   88.362 + 13.397W + 4.799H − 5.677A
Women: 447.593 + 9.247W + 3.098H − 4.330A

Katch-McArdle:

BMR = 370 + 21.6 × LBM
LBM = W × (1 − body fat% / 100)

Where W = kg, H = cm, A = years.

Worked example

Male, 30 years, 80 kg, 180 cm:

  • Mifflin-St Jeor: 10(80) + 6.25(180) − 5(30) + 5 = 800 + 1125 − 150 + 5 = 1,780 kcal
  • Harris-Benedict: 88.362 + 13.397(80) + 4.799(180) − 5.677(30) ≈ 1,934 kcal
  • Katch-McArdle (at 15% body fat, LBM = 68 kg): 370 + 21.6(68) ≈ 1,839 kcal

Notes

  • Sources: Mifflin (1990) Am J Clin Nutr 51:241-247; Roza & Shizgal (1984) Am J Clin Nutr 40:168-182.
  • BMR applies to adults. Children, pregnant women, and those with metabolic conditions should consult a clinician.

Frequently asked

Which BMR formula should I use?
Mifflin-St Jeor is recommended for most people — it's the most validated formula for general adults and is preferred by the Academy of Nutrition and Dietetics. Harris-Benedict (revised) is slightly older. Katch-McArdle is most accurate for people who know their body fat percentage, since it uses lean body mass rather than total weight.
What is BMR?
Basal Metabolic Rate is the number of calories your body burns in 24 hours at complete rest — no movement, digestion, or activity. It represents the minimum energy needed to maintain basic functions like breathing, circulation, and cell repair.
What's the difference between BMR and TDEE?
BMR is the resting baseline. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to account for exercise, work, and daily movement. Use the TDEE calculator once you have your BMR.
Why does the Katch-McArdle formula need body fat percentage?
Katch-McArdle calculates BMR from lean body mass (LBM = weight × (1 − body fat%)) rather than total weight. This makes it more accurate for people with above-average muscle mass or very low body fat, where weight-based formulas underestimate needs.
How accurate is BMR?
Mifflin-St Jeor predicts measured BMR within about ±10% for most healthy adults. Accuracy decreases at extreme body compositions. These are population-level equations; individual metabolism varies.