BMR calculator
Basal metabolic rate via Mifflin-St Jeor. The floor your body burns at rest, before training is added.
What you'll get: Your basal metabolic rate (BMR) in kcal per day — the energy your body uses at complete rest. Formula: Mifflin-St Jeor (Mifflin et al. 1990, PMID 2305711). Mifflin has the lowest error band among predictive BMR formulas for healthy adults (Frankenfield et al. 2005, PMID 16183355). For trained athletes the picture is harsher: O'Neill et al. 2023 (Sports Medicine, PMID 37632665) pooled 29 studies of 1 430 athletes and found Mifflin-St Jeor predicted only 45–56 % of male athletes within ±10 % of measured RMR; Fields et al. 2023 (Eur J Sport Sci, PMID 36168819) measured the mean error at ~400 kcal/day in male collegiate athletes. Individual variation is ±10–15 % even in non-athletes; for daily calorie targets that include training, use the TDEE calculator instead.
your BMR
what is BMR?
BMR (Basal Metabolic Rate) is the energy your body spends staying alive at complete rest — heart, lungs, brain, kidneys, cellular maintenance, body temperature. It excludes digestion, daily movement, and exercise. Typical adult BMR is 1300–2000 kcal/day; lifters with above-average muscle mass sit at the higher end of that range.
A related term, RMR (Resting Metabolic Rate), is measured under slightly less strict conditions and runs ~10 % higher than BMR. Most predictive equations — including Mifflin-St Jeor — technically predict RMR but are labelled BMR by convention. The gap sits inside their error band and doesn't change how you use the number.
Mifflin-St Jeor formula
The equation LiftGauge uses:
BMR (male) = 10·kg + 6.25·cm − 5·age + 5
BMR (female) = 10·kg + 6.25·cm − 5·age − 161
Mifflin and colleagues published it in 1990 using a sample of 498 adults, calibrated against indirect calorimetry. It replaced the older Harris-Benedict equation (1919) in most clinical and sports-science use after Frankenfield et al. 2005 tested four predictive equations against measured REE and found Mifflin had the smallest error band.
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):241–7. PMID 2305711.
why Mifflin beats Harris-Benedict
Harris-Benedict (1919) was the dominant BMR equation for most of the 20th century. The original sample was small and skewed toward young men; Roza & Shizgal's 1984 revision narrowed the gap but didn't fix the underlying bias.
Frankenfield, Roth-Yousey & Compher tested four predictive equations against indirect calorimetry. Mifflin-St Jeor predicted within 10 % of measured REE in about 70 % of healthy adults — Harris-Benedict managed 64 %. Mifflin also showed less bias in the obese subgroup, where Harris-Benedict systematically overpredicts.
For healthy adults of any weight, Mifflin-St Jeor is the modern default.
Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. J Am Diet Assoc 2005;105(5):775–89. PMID 16183355.
what BMR doesn't tell you
BMR is your resting floor. It does not include:
- Digestion (≈ 10 % of total intake, the thermic effect of food)
- Daily activity — steps, household, fidgeting (NEAT)
- Training (sets, conditioning, sport)
- Exercise recovery
A 90 kg lifter with a BMR of ~1900 kcal might burn 2700–3000 kcal on a real training day. To get the number you actually eat, multiply BMR by an activity factor (1.20–1.9 depending on weekly hours of training and job type). That number is TDEE — see the standalone TDEE calculator.
BMR for muscular adults
Lifters have more muscle than the population Mifflin-St Jeor was calibrated on. Lean body mass is the largest single driver of BMR — Wang et al. 2010 measured ~13 kcal/day per kg of skeletal muscle in resting metabolism. A lifter with 10 kg more lean mass than the Mifflin reference subject therefore burns ~130 kcal/day more than the equation predicts.
If you know your body-fat percent (DEXA, BodPod, or calibrated skinfold), the Katch-McArdle equation works directly from lean body mass and is more accurate for high-FFMI lifters. If you don't, Mifflin-St Jeor is the better default — it uses inputs everyone has (kg, cm, age, sex) and the under-prediction for muscular adults is typically smaller than the day-to-day variance of any predictive formula.
Wang Z, Heshka S, Heymsfield SB, Shen W, Gallagher D. Specific metabolic rates of major organs and tissues: a unified system. Am J Clin Nutr 2010;92(6):1369–77. PMID 20962155.
limitations
Predictive BMR equations have a measurement-error band of ±10–15 % against indirect calorimetry (ACSM GETP 11e, 2022, Ch. 7). Two adults with identical kg/cm/age can have BMRs that differ by 200–300 kcal/day from thyroid function, body composition, genetics, sleep, and chronic stress.
Use the calculator's output as a starting point. If you're using it as the base for a cut or bulk plan, eat at your predicted TDEE for 14 days, weigh in 5+ times per week, and adjust calories ±150 kcal if the trend doesn't match expectations.
Full provenance for every formula on this page is at /method §8.
frequently asked
- How accurate is the Mifflin-St Jeor BMR estimate?
- Within 10 % of measured resting energy expenditure for about 70 % of healthy adults (Frankenfield, Roth-Yousey & Compher 2005, PMID 16183355). The remaining 30 % fall outside ±10 % from thyroid, body composition, illness, or genetics. For most lifters, Mifflin is within 100–200 kcal/day of measured BMR — accurate enough as a starting point, but not a clinical reading.
- BMR vs RMR — what's the difference?
- BMR is measured after an overnight fast in a thermoneutral environment, lying still — the absolute resting floor. RMR uses slightly less strict conditions and runs ~10 % higher. Most predictive equations (Mifflin-St Jeor, Harris-Benedict) technically predict RMR even though they're labelled BMR; the gap sits inside their error band and doesn't change practical use.
- Should I use Mifflin-St Jeor or Katch-McArdle?
- If you know your body-fat percent (DEXA, BodPod, or a calibrated skinfold), Katch-McArdle uses lean body mass directly and is more accurate for muscular adults (Wang et al. 2010, PMID 20962155 shows LBM is the dominant BMR driver). If you don't have a body-fat measurement, Mifflin-St Jeor is the better default — it uses inputs you already have and is well-validated.
- What's the BMR formula for women vs men?
- Mifflin-St Jeor uses the same structure for both, with a sex offset: BMR (male) = 10·kg + 6.25·cm − 5·age + 5; BMR (female) = 10·kg + 6.25·cm − 5·age − 161. The 166-kcal gap captures average differences in lean body mass at the same height and weight. A muscular woman or smaller man will sit closer to the opposite-sex prediction.
- Why does my BMR drop when I lose weight?
- BMR scales with bodyweight in the Mifflin equation — every 5 kg lost drops predicted BMR by ~50 kcal/day. There's also a smaller separate effect called adaptive thermogenesis, where the body further reduces metabolic rate during prolonged calorie deficits (typically 50–100 kcal/day below the linear prediction after a long cut; Rosenbaum & Leibel 2010, Int J Obes 34:S47–55, PMID 20935667). Re-run the calculator every 4–6 weeks or after a bodyweight shift greater than 3 kg.
- Is BMR the number I should eat?
- No. BMR is the calories your body burns at complete rest. Eating at your BMR creates a large deficit for anyone who moves or trains — typically 600–1000+ kcal/day below maintenance. To get the number you should actually eat, multiply BMR by an activity factor — that's TDEE. Use the standalone TDEE calculator for that.