FormaGet FormaA resting estimate
Both equations predict resting energy from height, weight, age, and a published sex constant. Neither measures your oxygen consumption or body composition, and this is not a laboratory measurement.
Free BMR calculator
Calculate BMR with two published equations, side by side.
Most BMR calculators show one number from one equation. This one shows the Mifflin-St Jeor and revised Harris-Benedict estimates together, so you can see how much two well-known equations disagree for your inputs.
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Estimate BMR
Choose the units and published equation constants that fit the calculation.
This calculation runs locally and sends no data.
Mifflin-St Jeor
Revised Harris-Benedict
Difference
Formulas: Mifflin-St Jeor = 10 × weight in kg + 6.25 × height in cm − 5 × age, plus 5 with the male constant or minus 161 with the female constant. Revised Harris-Benedict (Roza and Shizgal, 1984) = 88.362 + 13.397 × kg + 4.799 × cm − 5.677 × age with the male constants, or 447.593 + 9.247 × kg + 3.098 × cm − 4.330 × age with the female constants.
What this result means
A visible disagreement
The difference between the two numbers is a reminder that equation choice alone can move an estimate. Treat the range as context, not as a confidence interval for your body.
A starting point
Resting energy is only part of daily expenditure. Use the TDEE calculator for an activity scenario, then compare it with repeated intake and bodyweight observations.
Which BMR equation is more accurate?
Mifflin-St Jeor
A 2005 systematic review of the four equations most used in clinical practice found Mifflin-St Jeor estimated resting metabolic rate within 10% of measured values in more nonobese and obese adults than the others, with the narrowest error range. It also found older adults and U.S. ethnic minorities underrepresented in the validation work.
Harris-Benedict
Roza and Shizgal re-derived the Harris-Benedict equations in 1984 and reported a precision of about 14% for normally nourished adults. A 2023 appraisal of five models against 353 individual measurements found the classic Harris-Benedict model closest to measured values in white adults.
What to take from both
The research does not name one equation that is right for everyone. Both papers report meaningful individual error, so a calculated BMR is a planning estimate to check against what your logs show over several weeks.
Public calculator, private product model
This tool intentionally uses two published equations and direct arithmetic. It does not reproduce Forma’s adaptive TDEE system. Forma can update an in-app estimate from logged calorie intake and smoothed bodyweight change, but its equations, coefficients, thresholds, confidence logic, and recommendation rules remain proprietary. Read the public methodology and limitations, the TDEE guide, and the calculator-accuracy guide.
Sources
Mifflin et al., 1990
The original Mifflin-St Jeor resting-energy prediction equation.
Roza and Shizgal, 1984
A re-evaluation of the Harris-Benedict equations reporting about 14% precision in normally nourished adults and poor reliability in malnourished patients.
Frankenfield et al., 2005
A systematic review comparing Harris-Benedict, Mifflin-St Jeor, Owen, and WHO/FAO/UNU equations against measured resting metabolic rate.
Westerterp, 2023
A critical appraisal comparing five prediction models with 353 individual resting energy measurements from 14 studies.
Sources last checked October 12, 2026. The coefficients above are the published values; results are rounded to the nearest kilocalorie.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy the body uses at complete rest to sustain basic functions. Calculators estimate it from body measurements with a prediction equation. They do not measure it.
Is BMR the same as RMR?
Not exactly. BMR is defined under strict basal conditions, while resting metabolic rate or resting energy expenditure is measured under less strict resting conditions. The equations on this page were developed and validated against resting measurements, so their results are best read as resting energy estimates.
Which BMR equation is most accurate?
No equation is accurate for every person. A 2005 systematic review found Mifflin-St Jeor estimated resting metabolic rate within 10% of measured values in more nonobese and obese adults than the other common equations it reviewed. A 2023 appraisal found the classic Harris-Benedict model closest to measured values in white adults. Both papers report meaningful individual error.
How do I get from BMR to daily calories?
Daily energy expenditure adds activity, digestion, and other movement on top of resting energy. The Forma TDEE calculator applies a visible activity multiplier to a Mifflin-St Jeor estimate. Repeated intake and bodyweight observations are a better guide than any single equation.
Check the estimate against your own record.
Track meals, calories, macros, steps, bodyweight trends, and training in Forma. For medical conditions, pregnancy, eating-disorder concerns, or individualized nutrition care, consult a qualified clinician.
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