Predictive equations are estimates: a 2005 systematic review found Mifflin-St Jeor within 10 % of measured resting energy for most adults, but not all.
At rest your body uses about 1,649 kcal a day by Mifflin-St Jeor; at the “moderately active” level that comes to about 2,556 kcal a day to hold your weight steady. The 3 formulas span 1,580–1,696 kcal at rest.
BMR by formula
Daily calories by activity level Rows: 5
Activity level
Factor
Mifflin-St Jeor
Harris-Benedict (revised)
Katch-McArdle
Sedentary
1.2
1,979
2,035
1,896
Lightly active
1.375
2,267
2,332
2,172
Moderately active
1.55
2,556
2,628
2,448
Very active
1.725
2,844
2,925
2,725
Extra active
1.9
3,133
3,222
3,001
How it's calculated S
Inputs in kilograms, centimetres and years
w=70kg,h=175cm,a=30
Lean body mass from body fat
LBM=70×(1−10020)=56.00kg
BMR by Mifflin-St Jeor
BMR=10×70+6.25×175−5×30+5=1,648.75kcal/day
Multiply by the activity factor
TDEE=1,648.75×1.55=2,555.56kcal/day
Calories are displayed as whole numbers, rounded half-up.
About the BMR and TDEE calculator
Basal metabolic rate (BMR) is the energy the body uses at complete rest. Mifflin-St Jeor computes it as 10 × weight in kg + 6.25 × height in cm − 5 × age in years, plus 5 for men or minus 161 for women; the revised Harris-Benedict equation and the Katch-McArdle equation, which works from lean body mass, are shown beside it. Total daily energy expenditure (TDEE) multiplies BMR by an activity factor from 1.2 (sedentary) to 1.9 (extra active).
TDEE is the usual starting point for a calorie target to lose, hold or gain weight. A 30-year-old man weighing 70 kg at 175 cm has a Mifflin-St Jeor BMR of 1,649 kcal a day, and at the moderately active factor of 1.55 his TDEE is about 2,556 kcal.
Both numbers are population estimates. Mifflin-St Jeor was fitted to 498 adults aged 19 to 78, and the activity factors are conventional multipliers rather than measurements, so an individual's measured needs can differ by 10 % or more.
Maintenance calories by activity level
Maintenance calories are your total daily energy expenditure (TDEE): BMR times an activity factor from 1.2 to 1.9. By Mifflin-St Jeor, a 30-year-old man of 70 kg and 175 cm needs about 1,979 kcal a day if sedentary and 2,556 kcal if moderately active.
All three equations for the same man, in kcal a day. Harris-Benedict is Roza and Shizgal's 1984 revision, not the 1919 original, and Katch-McArdle uses his lean mass, 56 kg at 20 % body fat:
Activity level
Factor
Mifflin TDEE
Revised Harris TDEE
Katch TDEE
Sedentary
1.2
1979
2035
1896
Lightly active
1.375
2267
2332
2172
Moderately active
1.55
2556
2628
2448
Very active
1.725
2844
2925
2725
Extra active
1.9
3133
3222
3001
Each row multiplies the three BMRs by the same factor, so the gap between the equations grows with activity: 139 kcal a day at the sedentary level, 221 kcal at the extra-active one.
Eating only his BMR, 1,649 kcal, would put him 330 kcal a day below maintenance even if sedentary. For the body fat percentage that Katch-McArdle needs, use the body fat calculator.
How to calculate BMR by hand
Basal metabolic rate (BMR) by the Mifflin-St Jeor equation is 10 × weight in kg + 6.25 × height in cm − 5 × age, then +5 for men or −161 for women. A 52-year-old woman who weighs 68 kg and is 163 cm tall: 680 + 1,018.75 − 260 − 161 = 1,277.75 kcal a day.
Mifflin-St Jeor was fitted to adults aged 19 to 78. Here is the same woman, who has 32 % body fat, through the other two equations:
Harris-Benedict (revised, women): 447.593 + 9.247 × 68 + 3.098 × 163 − 4.330 × 52 = 447.593 + 628.796 + 504.974 − 225.160 = 1,356.203 kcal. For men the constants are 88.362, 13.397, 4.799 and 5.677.
Katch-McArdle: lean mass is 68 × (1 − 0.32) = 46.24 kg, so BMR = 370 + 21.6 × 46.24 = 1,368.784 kcal. Sex and age do not enter this equation.
From BMR to TDEE
Total daily energy expenditure (TDEE) is BMR times an activity factor. If she is lightly active, Mifflin-St Jeor gives 1,277.75 × 1.375 = 1,756.9, or 1,757 kcal a day.
The same factor gives 1,865 kcal from Harris-Benedict and 1,882 kcal from Katch-McArdle. The three BMRs span 91 kcal, 7.1 % of the Mifflin figure. Keep every decimal until the last step and round only the final answer.
Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle
Mifflin-St Jeor and Harris-Benedict were fitted to resting energy measured by indirect calorimetry, which works out heat output from the oxygen a person breathes in and the carbon dioxide they breathe out.
The three equations differ in what they ask for and in how well they have held up when tested on new people:
Equation
Inputs
Built from
How it performed in later tests
Mifflin-St Jeor (1990)
Weight, height, age, sex
498 adults aged 19 to 78, 234 of them obese
More than 10 % off in 22 % of 130 adults; under 50 % accurate in recreational athletes
Harris-Benedict, Roza-Shizgal revision (1984)
Weight, height, age, sex
The 1919 Harris-Benedict subjects plus 98 more from Benedict's later work
More than 10 % off in 33 % of the same 130 adults, and in 36 % of the obese ones
Katch-McArdle
Lean body mass only
Cunningham's 1991 review of lean-mass studies
A lean-mass equation of the same form was the accurate one in athletes
The 130-adult comparison is Frankenfield and colleagues (2003), whose volunteers had BMIs from 18.8 to 96.8. The Owen equation, tested alongside, missed by more than 10 % in 35 %.
Their abstract does not name the Harris-Benedict version tested; the athlete study below used the 1984 revision.
Ten Haaf and Weijs (2014) measured 90 recreational athletes training about nine hours a week. Mifflin-St Jeor, Harris-Benedict, WHO, Schofield and Owen each predicted fewer than half of them within 10 %.
Cunningham's lean-mass equation, 500 + 22 × lean mass in kg, did so for 85 % of the men and 78 % of the women. Katch-McArdle, 370 + 21.6 × lean mass, has the same structure.
Its constants are the ones Cunningham proposed in a 1991 review, where lean mass explained 65 to 90 % of the variation in resting energy.
Cunningham (1980) had reanalyzed 223 of Harris and Benedict's original subjects. Lean body mass alone predicted their basal metabolic rate, and sex and age added little once it was known.
In practice, start with Mifflin-St Jeor, which did best in the 130-adult comparison. Switch to Katch-McArdle if you are muscular or train hard and have a body fat figure from a reliable method.
TDEE activity multipliers
An activity factor is the ratio of total daily energy use to BMR. The FAO/WHO/UNU expert consultation calls the same ratio the physical activity level (PAL), and its 2004 report on human energy requirements gives measured ranges for it.
The last column places each factor in those ranges. The TDEE figures are for the woman above.
Activity level
Factor
Description
TDEE (Mifflin)
FAO/WHO/UNU lifestyle band
Sedentary
1.2
Desk job, little or no exercise
1,533 kcal
Below the lowest band (1.40)
Lightly active
1.375
Light exercise 1–3 days a week
1,757 kcal
Below the lowest band
Moderately active
1.55
Moderate exercise 3–5 days a week
1,981 kcal
Sedentary or light, 1.40 to 1.69
Very active
1.725
Hard exercise 6–7 days a week
2,204 kcal
Active or moderately active, 1.70 to 1.99
Extra active
1.9
Physical job or training twice a day
2,428 kcal
Active or moderately active, 1.70 to 1.99
The two lowest factors are conservative. A meta-analysis the report cites found a typical PAL of 1.60 in 411 adults with a mostly sedentary Western lifestyle, and an obesity task force suggested 1.50 to 1.55 for sedentary people.
For the woman above, the gap between the sedentary factor and a PAL of 1.60 is 511 kcal a day. The report's sedentary examples, office workers who drive and rarely exercise, start at 1.40, above the lightly active factor.
The report treats a PAL of 1.21, close to the sedentary factor, as a short-term survival figure for totally inactive, dependent people. Its vigorous band runs from 2.00 to 2.40.
An hour a day of jogging, cycling or similar exercise raises PAL from about 1.55 to 1.75.
What BMR measures and what TDEE adds
Basal metabolic rate is measured awake and lying down, after 10 to 12 hours without food and 8 hours of physical rest, relaxed, at a room temperature that neither chills nor warms you.
Mifflin-St Jeor was fitted to resting energy expenditure (REE, also called RMR), though most sources still call its result BMR.
A guessed body fat in Katch-McArdle. Each 5 percentage points shifts this woman's lean mass by 3.4 kg and her BMR by 73 kcal.
Choosing the level from gym sessions alone. The FAO bands describe a whole lifestyle, including work and getting around.
Treating the number as exact. Even with Mifflin-St Jeor, one person in five was more than 10 % off in Frankenfield's test. At 1,757 kcal, 10 % is 176 kcal a day.
Using it outside the fitted range. Mifflin-St Jeor was built on adults up to 78.
Check the estimate against your weight trend
The most reliable check is your own weight. If it holds steady for two or three weeks on a known intake, that intake is your real TDEE.
BMR is the energy used at complete rest to keep the body running; TDEE adds the energy spent moving and digesting food. TDEE is BMR times an activity factor: 1.2 for sedentary, 1.375 lightly active, 1.55 moderately active, 1.725 very active and 1.9 extra active. A BMR of 1,649 kcal becomes 1,979 kcal a day at the sedentary factor and 2,556 kcal at 1.55.
Which BMR formula is most accurate?
For most adults, Mifflin-St Jeor. A 2005 systematic review for the American Dietetic Association (Frankenfield and colleagues) found it predicted resting metabolic rate within 10 % of the measured value in more non-obese and obese people than the Harris-Benedict, Owen or WHO/FAO/UNU equations, with the narrowest error range. Katch-McArdle works from lean mass instead, so its accuracy depends on the body fat figure entered.
Does BMR go down with age?
Yes. In the Mifflin-St Jeor equation BMR falls by 5 kcal a day for each year of age at the same weight and height, so a 70 kg, 175 cm man drops from 1,649 kcal at 30 to 1,549 kcal at 50. Much of the fall reflects loss of lean mass: Mifflin and colleagues found fat-free mass the best single predictor of resting energy expenditure (R² = 0.64).
Why is Harris-Benedict higher than Mifflin-St Jeor?
Harris-Benedict was fitted in 1919 to 239 people, and Mifflin and colleagues found in 1990 that it overestimated measured resting energy by 5 %. Roza and Shizgal's 1984 revision, used here, refitted the data with 98 more subjects and reports a precision of ±14 %. For the default 30-year-old man it gives 1,696 kcal, 2.8 % above Mifflin-St Jeor's 1,649 kcal.
For information only, not medical advice. These formulas describe populations, not you; talk to a clinician before acting on a result.
Checked against references
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