What Is BMR?
Basal Metabolic Rate (BMR) estimates calories burned at complete rest — breathing, circulation, cell repair. It is closely related to Resting Metabolic Rate (RMR), which uses slightly less strict measurement conditions and is often a few percent higher. For a deep dive on the Mifflin-St Jeor equation specifically — including TDEE tables and goal calories — see our dedicated calculator. The National Academies energy framework describes resting energy as the largest component of total daily expenditure for most adults.
BMR vs RMR vs TDEE
Metric
What it measures
Best use
Metric
What it measures
Best use
Metric
What it measures
Best use
| Metric | What it measures | Best use |
|---|---|---|
| BMR | Calories at complete rest (strict conditions) | Research baseline; calculator estimates |
| RMR | Resting energy under less strict conditions | Often 3–10% higher than BMR in lab settings |
| TDEE | BMR × activity + digestion (TEF) | Daily calorie planning and deficits |
How This Calculator Works
Four steps — all running locally in your browser.
Inputs
Age, sex, height, weight
Formula
Mifflin-St Jeor default
Compare
Side-by-side formula spread
Interpret
Range + TDEE conversion
Formula Comparison
Frankenfield et al. (2005) found Mifflin-St Jeor within ~10% of measured RMR for roughly 82% of normal-weight adults. Formulas can differ by 100–300 kcal — pick one and calibrate from weight trends.
Mifflin-St Jeor (default)
Male:
BMR = (10 × kg) + (6.25 × cm)
− (5 × age) + 5
Female:
BMR = (10 × kg) + (6.25 × cm)
− (5 × age) − 161- kg
- Body weight in kilograms
- cm
- Height in centimeters
- age
- Age in years
Revised Harris-Benedict
Male:
BMR = 88.362 + (13.397 × kg)
+ (4.799 × cm) − (5.677 × age)
Female:
BMR = 447.593 + (9.247 × kg)
+ (3.098 × cm) − (4.330 × age)- kg
- Body weight in kilograms
- cm
- Height in centimeters
- age
- Age in years
May run slightly higher on average — useful as a cross-check.
Katch-McArdle
Lean mass (kg) = weight (kg)
× (1 − body fat % / 100)
BMR = 370 + (21.6 × lean mass kg)- kg
- Body weight in kilograms
- BF%
- Body fat percentage (required)
Requires reliable body fat %. Skip if BF% is guessed.
Worked Examples
Example: 35-year-old man, 180 cm, 80 kg
Using Mifflin-St Jeor.
- BMR = (10 × 80) + (6.25 × 180) − (5 × 35) + 5
- BMR = 800 + 1,125 − 175 + 5 = 1,755 kcal/day
Result: Estimated BMR ≈ 1,755 kcal/day (±10% practical range in results)
Example: 30-year-old woman, 165 cm, 62 kg
Using Mifflin-St Jeor.
- BMR = (10 × 62) + (6.25 × 165) − (5 × 30) − 161
- BMR = 620 + 1,031 − 150 − 161 = 1,340 kcal/day
Result: Estimated BMR ≈ 1,340 kcal/day
How to Interpret Your BMR
What your result means and what to do next.
Your BMR range
What it means
Next step
Your BMR range
What it means
Next step
Your BMR range
What it means
Next step
| Your BMR range | What it means | Next step |
|---|---|---|
| Within ±10% band | Typical accuracy for population equations | Multiply by activity factor for TDEE |
| Formula spread >150 kcal | Equations disagree — normal for your inputs | Pick one formula; calibrate from trends |
| BMR seems low/high | Individual variation exists beyond formulas | Use 2–3 week weight trend as ground truth |
Accuracy & Limitations
TDEE estimate error comes from two stacked layers — and the second is usually bigger in practice.
Layer 1: BMR formula error
Mifflin-St Jeor predicts resting metabolic rate within ~10% for roughly 82% of non-obese adults and ~70% of obese adults (Frankenfield et al., 2005). That is ±150–200 kcal for many people.
Layer 2: Activity multiplier error
Picking one activity bucket too high adds ~200–400 kcal/day. Most people remember gym time but underestimate desk hours. Take our Activity Level Quiz if unsure.
Common Mistakes
- Eating at BMR only — most people need more once daily activity is included.
- Using Katch-McArdle with guessed body fat — inaccurate BF% can make this worse than Mifflin-St Jeor.
- Expecting BMR to stay fixed — recalculate when weight changes by ~5 kg (10 lb).
- Picking the highest formula — formula spread is usually smaller than activity error.
- Ignoring age effects — BMR tends to decline gradually; formulas account for this.
- Confusing BMR with TDEE — use the full TDEE calculator for daily planning.
Myths vs Facts
Myth
Lower BMR means you are broken or in starvation mode.
Evidence-based view
BMR changes with weight, age, and muscle mass. A smaller body generally needs fewer calories — that is expected.
Myth
The formula with the highest number is most accurate for you.
Evidence-based view
Pick one formula, then calibrate from 2–3 weeks of weight trends. Formula spread is usually smaller than activity error.
Myth
BMR and RMR are identical.
Evidence-based view
RMR is measured under less strict conditions and is often slightly higher than BMR.
Myth
You should eat exactly at your BMR to lose fat.
Evidence-based view
Fat loss requires a deficit below TDEE (maintenance), not necessarily at BMR. Very low targets may be harder to sustain — consider a smaller deficit.
Safety & Limitations
Research & References
Each citation below supports a specific claim on this page. We explain relevance so you can verify the science yourself.
- National Academies of Sciences, Engineering, and Medicine — Factors Affecting Energy Expenditure and Requirements. Dietary Reference Intakes for Energy — NCBI Bookshelf, 2023.Defines TDEE components (REE, TEF, PAEE) and explains why population equations cannot capture individual metabolic variation.
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247, 1990.DOI: 10.1093/ajcn/51.2.241Primary source for the Mifflin-St Jeor BMR equation used as the default in this calculator.
- Roza AM, Shizgal HM — The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182, 1984.DOI: 10.1093/ajcn/40.1.168Source for the revised Harris-Benedict coefficients offered as a comparison formula.
- McArdle WD, Katch FI, Katch VL — Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins, 7th edition, 2010.Textbook reference for the lean-body-mass-based Katch-McArdle resting energy estimate.
- Frankenfield D, Roth-Yousey L, Compher C — Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. J Am Diet Assoc. 2005;105(5):775-789, 2005.DOI: 10.1016/j.jada.2005.02.005Meta-analysis showing Mifflin-St Jeor within ~10% of measured RMR for ~82% of non-obese and ~70% of obese adults — supports honest accuracy framing.
Frequently Asked Questions
Common questions about the bmr calculator.