BMR Calculator
Calculate your Basal Metabolic Rate — the calories your body burns at complete rest.
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
Pick your units
Imperial (lb / ft / in) or metric (kg / cm). The form swaps over instantly.
- 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
Want more precision? Open Advanced
Add your body fat % and switch to a body-composition formula (Katch-McArdle or Cunningham), better for lean or muscular bodies where weight-based equations under-predict.
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Read your results
Your BMR appears with a ±5% range. Switch between the five supported formulas in Advanced to see how different equations compare.
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 roughly 10–15% 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 five of them.
Mifflin-St Jeor (1990)
The default formula and the Academy of Nutrition and Dietetics' recommended equation for non-critically-ill adults. Frankenfield's 2005 meta-analysis (the AND Evidence Analysis Library basis) placed it within ±10% of measured RMR in 82% of non-obese and ~70% of obese adults, the highest hit rate among the predictive equations tested. Validated for 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) / Cunningham (1991) — body-fat-based path
Katch-McArdle and Cunningham are algebraically identical; both are listed because they cite different validation populations. They use lean body mass directly and perform best in lean and trained populations where fat-free mass (FFM) dominates BMR. In mixed-BMI general populations, FFM-based equations can systematically underestimate BMR (Kfir et al. 2023, Nutrients 15(4):805, n=3,001 with mean BMI 28.5, reported −16.6% mean bias for Cunningham across the cohort), so this path is opt-in for users who specifically want a body-composition estimate.
BMR = 370 + 21.6 × LBM
LBM = lean body mass (kg) = weight × (1 − bodyfat% / 100)
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 a 1984 revision of 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. The ±5% range we display is a deliberately tight, illustrative band; true individual error is wider, roughly ±10%, so your real BMR can fall outside it.
Factors not captured by the equation include thyroid status, certain medications (beta-blockers lower BMR ~5–10%), pregnancy/lactation, and recent weight-loss history.