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

BMR

What it measures

Calories at complete rest (strict conditions)

Best use

Research baseline; calculator estimates

Metric

RMR

What it measures

Resting energy under less strict conditions

Best use

Often 3–10% higher than BMR in lab settings

Metric

TDEE

What it measures

BMR × activity + digestion (TEF)

Best use

Daily calorie planning and deficits

How This Calculator Works

Four steps — all running locally in your browser.

1

Inputs

Age, sex, height, weight

2

Formula

Mifflin-St Jeor default

3

Compare

Side-by-side formula spread

4

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.

For a body-fat-first lean-mass workflow with Navy estimation, use the Katch-McArdle Calculator. When you already have measured lean mass, the Cunningham RMR Calculator supports direct LBM entry. For age-specific WHO BMR from infancy through older adults (weight-only), use the Schofield Calculator. For the simplest adult weight-only Owen RMR (1986/1987), use the Owen Calculator. To compare all seven equations with auto-select, TDEE, and goals, use the REE Calculator or RMR Calculator.

Worked Examples

Example: 35-year-old man, 180 cm, 80 kg

Using Mifflin-St Jeor.

  1. BMR = (10 × 80) + (6.25 × 180) − (5 × 35) + 5
  2. 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.

  1. BMR = (10 × 62) + (6.25 × 165) − (5 × 30) − 161
  2. 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

Within ±10% band

What it means

Typical accuracy for population equations

Next step

Multiply by activity factor for TDEE

Your BMR range

Formula spread >150 kcal

What it means

Equations disagree — normal for your inputs

Next step

Pick one formula; calibrate from trends

Your BMR range

BMR seems low/high

What it means

Individual variation exists beyond formulas

Next step

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

Suggested next steps

BEE Calculator

Basal energy + auto-select across 7 equations

Fat-Free Mass Calculator

FFM from body fat % before Katch/Cunningham

Lean Body Mass Calculator

Anthropometric LBM when BF% unknown

RMR Calculator

RMR hub, fixed kcal goals & macro preview

REE Calculator

All 7 equations, auto-select, TDEE & goals

Full TDEE Calculator

Add activity and goal to your BMR estimate

Maintenance Calculator

Maintenance calories from BMR + activity

Activity Level Quiz

Get a realistic activity multiplier

Calorie Surplus Calculator

Bulking presets from your BMR estimate

Harris-Benedict Calculator

Original (1919) and revised (1984) BMR equations

Methodology

Every formula and coefficient with sources

Frequently Asked Questions

Common questions about the bmr calculator.

What is BMR?
BMR (Basal Metabolic Rate) estimates calories your body uses at complete rest to maintain basic functions like breathing, circulation, and cell repair. It is typically the largest single component of total daily energy use — often 60–75% for sedentary adults.
How is BMR different from TDEE?
BMR is resting energy only. TDEE adds activity (NEAT, exercise) and the thermic effect of food on top of BMR. For calorie planning, TDEE is the more complete starting point.
Which BMR formula should I use?
Mifflin-St Jeor is the default for most adults and performs well in comparative research. Katch-McArdle works when you have a reliable body fat percentage. Harris-Benedict is useful as a cross-check.
How accurate is a BMR calculator?
BMR equations are population-level estimates that may vary ±10–15% from measured values for any individual. Frankenfield et al. (2005) found Mifflin-St Jeor within ~10% for roughly 82% of adults in lower body weight ranges.
Does BMR change with weight loss?
Yes. As body weight decreases, estimated BMR typically decreases as well because a smaller body requires less energy. Recalculate when your weight changes by more than ~5 kg (10 lb).
Should I eat at my BMR?
Most people need more than BMR because daily life and activity add energy needs. BMR is a baseline for understanding metabolism, not a full-day eating target.
Does age affect BMR?
Yes. BMR formulas include age because resting metabolic rate tends to decline gradually over the lifespan, partly due to changes in body composition and organ metabolism.
Is BMR the same as resting metabolic rate?
They are closely related but not identical. RMR is measured under less strict conditions than BMR and is often slightly higher — typically by 3–10% in research settings.
Can I use BMR for weight loss?
BMR alone is not enough for planning intake. Use TDEE (BMR plus activity) as a more complete starting point, then apply a deficit below maintenance if fat loss is your goal.
Does this calculator store my data?
No. All calculations run locally in your browser. Nothing you enter is sent to a server.
Why do different formulas give different BMR?
Each formula was derived from different study populations and inputs, so results can differ by 100–300 calories. Compare formulas side-by-side in your results, pick one, and calibrate from weight trends.
How do I convert BMR to TDEE?
Multiply BMR by an activity factor (1.2 sedentary through 1.9 extra active) or use our full TDEE Calculator on the homepage for goal calories and macros.

Research & References

Each citation below supports a specific claim on this page. We explain relevance so you can verify the science yourself.

  1. 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.
  2. 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.Primary source for the Mifflin-St Jeor BMR equation used as the default in this calculator.
  3. 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.Source for the revised Harris-Benedict coefficients — default equation on this calculator page.
  4. 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.
  5. 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.Meta-analysis showing Mifflin-St Jeor within ~10% of measured RMR for ~82% of non-obese and ~70% of obese adults — supports honest accuracy framing.
  6. Frankenfield DC, Rowe WA, Smith JS, Cooney RN — Validation of several established equations for resting metabolic rate in obese and nonobese people. J Am Diet Assoc. 2003;103(9):1152-1159, 2003.Direct validation showing standard Harris-Benedict within ±10% of measured RMR in ~67% of adults vs ~78% for Mifflin-St Jeor in the same cohort.
  7. Harris JA, Benedict FG — A Biometric Study of Basal Metabolism in Man. Carnegie Institution of Washington Publication No. 279, 1919.Original Harris-Benedict basal metabolism equations (1919) — historical baseline superseded by the 1984 revision for most modern adults.
  8. O'Neill JER, Corish CA, Horner K — Accuracy of Resting Metabolic Rate Prediction Equations in Athletes: A Systematic Review with Meta-analysis. Sports Med. 2023;53(12):2373-2398, 2023.Athlete systematic review and meta-analysis — several common equations including Mifflin-St Jeor and Owen differed significantly from measured RMR in pooled athlete data; lean-mass equations (e.g., Cunningham 1980) and Ten-Haaf performed differently by population, with no single best equation for all athletes.
  9. Cunningham JJ — A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr. 1980;33(11):2372-2374, 1980.Primary source for the Cunningham equation (500 + 22 × lean body mass kg). Cunningham’s paper labels the output BMR; the 1980 reanalysis of Harris-Benedict (1919) data found LBM as the single predictor, with sex and age adding little once LBM was included.
  10. Schofield WN — Predicting basal metabolic rate, new standards and review of previous work. Hum Nutr Clin Nutr. 1985;39 Suppl 1:5-41, 1985.Primary source for the Schofield age- and sex-specific BMR predictive equations (weight-only kcal/day form retained in FAO/WHO Table 5.2).
  11. Owen OE, Kavle EC, Owen RS, Polansky M, Caprio S, Mozzoli MA, Kendrick ZV, Bushman MC, Boden G — A reappraisal of caloric requirements in healthy women. Am J Clin Nutr. 1986;44(1):1-19, 1986.Primary source for Owen female RMR equations — non-athlete (795 + 7.18 × weight kg) and athlete (50.4 + 21.1 × weight kg) variants.
  12. Owen OE, Holup JL, D'Alessio DA, Craig ES, Polansky M, Smalley KJ, Kavle EC, Bushman MC, Owen LR, Mozzoli MA, Kendrick ZV, Boden G — A reappraisal of the caloric requirements of men. Am J Clin Nutr. 1987;46(6):875-885, 1987.Primary source for Owen male RMR equation (879 + 10.2 × weight kg) in men 18–82 years; found weight alone predicted RMR with age effect trivial.