BMR calculator

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 the equation in 1990 using 498 adults and measured resting energy expenditure. It is a population-derived estimate; an individual can differ from the prediction.

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 this calculator uses Mifflin-St Jeor

Harris-Benedict and Mifflin-St Jeor are population-derived equations for resting energy expenditure. Their performance depends on the population in which they are evaluated.

Frankenfield, Roth-Yousey & Compher (2005) reviewed validation studies of four commonly used equations. Mifflin-St Jeor performed better within a 10 % accuracy criterion in more of the included comparisons, but clinically important individual errors remained. This does not guarantee that every user falls within that band.

This calculator uses Mifflin-St Jeor because it needs readily available inputs. A measured resting metabolic rate may be more appropriate when an accurate individual assessment is needed.

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 15883556.

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

Body composition matters, but not all fat-free tissue has the same resting energy cost. Wang et al. (2010) evaluated an organ-and-tissue model, including a reference estimate of about 13 kcal per kilogram of skeletal muscle per day. This does not establish a fixed correction to Mifflin-St Jeor or validate Katch-McArdle for every muscular adult.

A lean-mass equation also depends on the accuracy of the body-composition estimate. A different equation is not automatically more accurate for you. Interpret both as estimates rather than adding a fixed muscle-related calorie correction.

Wang Z, Ying Z, Bosy-Westphal A, et al. Specific metabolic rates of major organs and tissues across adulthood: evaluation by mechanistic model of resting energy expenditure. Am J Clin Nutr 2010;92(6):1369–77. Study abstract.

limitations

Predictive equations can differ substantially from an individual’s measured resting expenditure. Error depends on the equation, population, body composition and measurement conditions; a fixed ±10–15 % band is not an individual guarantee.

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.

method notes

O’Neill et al. (2023, review) included 29 studies and 1,430 athletes and found substantial differences in accuracy and precision across equations. Fields et al. (2023, study) compared ten equations in 187 collegiate athletes; errors depended on equation and sex. Resting expenditure is only one component of total daily energy expenditure.

frequently asked

How accurate is the Mifflin-St Jeor BMR estimate?

Individual error can be substantial. Frankenfield, Roth-Yousey & Compher (2005, review) compared resting-metabolism equations and found Mifflin-St Jeor useful in the studied populations, but not uniformly accurate. This result is a starting estimate, not a measurement or a guaranteed 100–200 kcal error range.

BMR vs RMR — what's the difference?

BMR refers to measurements under stricter basal conditions, while RMR is measured under less restrictive resting conditions. Mifflin-St Jeor estimates resting energy expenditure even though this page uses the familiar BMR label. Neither includes all daily activity, and there is no universal percentage conversion between the two.

Should I use Mifflin-St Jeor or Katch-McArdle?

Mifflin-St Jeor uses weight, height, age and sex; Katch-McArdle uses an estimate of lean body mass. A body-fat measurement introduces its own uncertainty. Wang et al. (2010) studied tissue metabolism, not a comparison proving that Katch-McArdle is better for lifters.

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 two constant terms differ by 166 kcal/day. These are population regression coefficients, not a measured difference between any two individuals.

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.