Mifflin-St Jeor Equation: BMR Formula & Examples

The Mifflin-St Jeor equation estimates your basal metabolic rate (BMR), the calories your body burns at complete rest. For men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. For women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age − 161. It is the BMR formula dietitians use by default, because a 2005 systematic review found it was more likely than other common equations to land within 10% of measured metabolic rate.

That one number underpins almost every calorie target you will ever see. TDEE calculators, macro calculators, and weight loss apps all start with BMR and build from there. If the starting point is off, everything downstream is off too.

This guide covers the formula itself, worked examples in both metric and imperial units, how the Mifflin-St Jeor equation stacks up against Harris-Benedict and Katch-McArdle, what the accuracy research actually says, and how to go from BMR to total daily calories. It also covers why your step count is a better way to do that last step than an activity dropdown.

Want the number without the math? Plug your stats into the BMR calculator, which runs Mifflin-St Jeor alongside the other two major formulas so you can see the spread.

What Is the Mifflin-St Jeor Equation?

The Mifflin-St Jeor equation is a prediction formula for resting energy expenditure. It was published in 1990 in the American Journal of Clinical Nutrition by Mark Mifflin, Sachiko St Jeor, and colleagues, in a paper titled "A new predictive equation for resting energy expenditure in healthy individuals."

The researchers measured the resting metabolism of 498 healthy adults (251 men and 247 women) using indirect calorimetry, which calculates energy use from the oxygen you breathe in and the carbon dioxide you breathe out. Participants were 19 to 78 years old, and the group included both normal-weight (264) and obese (234) people. That mix matters: the older Harris-Benedict equation was built on a smaller, younger, leaner group in the 1910s.

From that data, they derived a simple equation using four inputs: weight, height, age, and sex. In the same paper, they reported that the original Harris-Benedict equation overestimated measured resting metabolism by about 5% in their sample.

BMR vs RMR: Does the Difference Matter?

Strictly speaking, Mifflin-St Jeor predicts resting metabolic rate (RMR), not basal metabolic rate. True BMR is measured under strict lab conditions: overnight fast, just after waking, lying still in a temperature-controlled room. RMR is measured under looser conditions and runs slightly higher.

In practice the gap is small, and nearly every calculator (ours included) uses the terms interchangeably. If you want the full picture of how BMR fits with your other daily calorie burns, see BMR vs TDEE.

The Mifflin-St Jeor Equation for Men and Women

The formula is identical for both sexes except for the final constant.

Metric version (kg, cm):

Men:   BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age) − 161

Imperial version (lb, inches):

Men:   BMR = (4.536 × weight in lb) + (15.88 × height in inches) − (5 × age) + 5
Women: BMR = (4.536 × weight in lb) + (15.88 × height in inches) − (5 × age) − 161

The imperial coefficients are just the metric ones converted: 10 per kilogram becomes 4.536 per pound, and 6.25 per centimeter becomes about 15.88 per inch. Both versions give the same answer.

The 166-calorie gap between the male (+5) and female (−161) constants reflects the fact that, at the same weight and height, women typically carry more fat mass and less lean mass, and lean mass is what drives resting metabolism.

Input	Effect on BMR
Each extra kg of body weight	+10 calories
Each extra lb of body weight	about +4.5 calories
Each extra cm of height	+6.25 calories
Each extra inch of height	about +15.9 calories
Each extra year of age	−5 calories
Male vs female (same size and age)	+166 calories

Worked Example: Mifflin-St Jeor in kg and cm

A 35-year-old woman, 70 kg, 165 cm tall:

Weight: 10 × 70 = 700
Height: 6.25 × 165 = 1,031.25
Age: 5 × 35 = 175
Combine: 700 + 1,031.25 − 175 − 161 = 1,395 calories per day

So her body burns roughly 1,395 calories a day just keeping her alive: breathing, circulating blood, maintaining body temperature, and running her organs. A large share of that happens overnight, which is why calories burned sleeping track so closely with BMR.

Worked Example: Mifflin-St Jeor in Pounds and Inches

A 40-year-old man, 180 lb, 5 ft 10 in (70 inches) tall:

Weight: 4.536 × 180 = 816.5
Height: 15.88 × 70 = 1,111.6
Age: 5 × 40 = 200
Combine: 816.5 + 1,111.6 − 200 + 5 = about 1,733 calories per day

Run the same man through the metric version (81.6 kg, 177.8 cm) and you get the same 1,733. We will use both of these people for the comparisons below.

Mifflin-St Jeor vs Harris-Benedict vs Katch-McArdle

There are three BMR formulas you will see on most calculators. Here is what each one does.

Harris-Benedict Equation (Original, 1918–1919)

The Harris-Benedict equation was the clinical standard for most of the 20th century. It was developed by James Harris and Francis Benedict at the Carnegie Institution using a group of mostly young, healthy, normal-weight adults.

Men:   BMR = 66.5 + (13.75 × kg) + (5.003 × cm) − (6.755 × age)
Women: BMR = 655.1 + (9.563 × kg) + (1.850 × cm) − (4.676 × age)

Revised Harris-Benedict Equation (Roza and Shizgal, 1984)

In 1984, Roza and Shizgal re-fit the Harris-Benedict equation using the original data plus newer measurements. This revised version is what most "Harris-Benedict" calculators actually use today.

Men:   BMR = 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age)
Women: BMR = 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age)

Katch-McArdle Formula

Katch-McArdle ignores sex, height, and age entirely. It uses only your lean body mass (your weight minus your fat mass):

BMR = 370 + (21.6 × lean body mass in kg)

Because lean tissue is what burns most of your resting calories, this formula can be the most accurate of the three for lean or muscular people. The catch: it needs a reasonably good body fat percentage, and a bad estimate gives a bad answer. The body fat calculator can give you a starting estimate from tape measurements.

Side-by-Side Comparison

Here are our two example people run through all four equations. For Katch-McArdle, we assume 30% body fat for the woman and 20% for the man.

Formula	Woman (35, 70 kg, 165 cm)	Man (40, 180 lb, 5'10")
Mifflin-St Jeor (1990)	1,395	1,733
Harris-Benedict, original	1,466	1,809
Harris-Benedict, revised	1,455	1,808
Katch-McArdle	1,428	1,781

The pattern is typical: both Harris-Benedict versions come out 60 to 75 calories higher than Mifflin-St Jeor for average adults, consistent with the roughly 5% overestimate reported in the 1990 paper. Multiply that by an activity factor of 1.5 or so and the gap grows to about 100 calories a day, which adds up over months of dieting.

	Mifflin-St Jeor	Harris-Benedict	Katch-McArdle
Inputs	Weight, height, age, sex	Weight, height, age, sex	Lean body mass only
Study population	498 adults incl. obese, ages 19–78	Small, young, mostly lean group	Varies by source
Tends to	Be the most reliable for most adults	Run slightly high	Be best for lean, muscular people
Needs body fat %?	No	No	Yes

How Accurate Is the Mifflin-St Jeor Equation?

The strongest evidence comes from a 2005 systematic review in the Journal of the American Dietetic Association by Frankenfield, Roth-Yousey, and Compher. The review compared the four equations most used in clinical practice (Harris-Benedict, Mifflin-St Jeor, Owen, and WHO/FAO/UNU) against measured resting metabolic rate in healthy non-obese and obese adults.

Its conclusion: the Mifflin-St Jeor equation was more likely than the other equations to predict resting metabolic rate within 10% of the measured value. That finding is the main reason the Academy of Nutrition and Dietetics (formerly the American Dietetic Association) and most modern calculators default to Mifflin-St Jeor.

The same review was clear about the limits:

Individual errors still happen. "Most likely to be within 10%" is not "always within 10%." Some people will be off by more than that in either direction.
Some groups were underrepresented. Older adults and US ethnic minorities were underrepresented in both the development and validation of these equations, so accuracy for those groups is less certain.
Measurement beats prediction when it matters. For clinical cases where the formula clearly fails someone, the authors pointed to indirect calorimetry as the better tool.

For a 1,700-calorie BMR, a 10% error is about 170 calories a day. That is why any BMR formula should be treated as a starting estimate, then adjusted based on what your weight actually does over 2 to 4 weeks.

When Mifflin-St Jeor Is Less Accurate

Very muscular people and athletes. More lean mass per kilogram means a higher real BMR than the formula predicts. Katch-McArdle is usually the better choice here.
Very high body fat. The formula can overestimate, since it treats each kilogram as roughly equal regardless of whether it is fat or muscle.
Pregnancy, illness, injury, and some medications. All of these change energy needs in ways four simple inputs cannot capture.

Activity Factor Chart: From BMR to TDEE

BMR only covers the calories you burn at rest. To get your total daily energy expenditure (TDEE), the calories you burn including all movement, you multiply BMR by an activity factor. These are the standard multipliers used by most calculators, including our TDEE calculator:

Activity Level	Description	Activity Factor
Sedentary	Desk job, little or no exercise	1.2
Lightly active	Light exercise 1–3 days per week	1.375
Moderately active	Moderate exercise 3–5 days per week	1.55
Very active	Hard exercise 6–7 days per week	1.725
Extremely active	Physical job or twice-daily training	1.9

Applied to our two Mifflin-St Jeor results:

Activity Level	Woman (BMR 1,395)	Man (BMR 1,733)
Sedentary (1.2)	1,674	2,080
Lightly active (1.375)	1,918	2,383
Moderately active (1.55)	2,162	2,686
Very active (1.725)	2,406	2,989
Extremely active (1.9)	2,650	3,293

For a deeper look at what TDEE includes, read what is TDEE.

Why Step-Based TDEE Beats Activity Multipliers

Look at the man's column above. Moving from "lightly active" to "moderately active" adds about 300 calories a day, and the only thing deciding which row he picks is his own guess. Is a teacher who is on her feet all day "lightly" or "moderately" active? What about someone who walks the dog twice a day but never goes to a gym? The labels are vague, and people tend to overrate their own activity.

If you walk for most of your exercise, you already have a better input: your daily step count. The method:

Calculate BMR with the Mifflin-St Jeor equation.
Multiply by the sedentary factor of 1.2 only.
Add calories from your average daily steps: steps × weight (kg) × 0.0005.
Add any non-walking exercise (cycling, swimming, lifting) separately.

Here is how it plays out for our 180 lb (81.6 kg) man with a sedentary baseline of 2,080 calories:

Average Daily Steps	Calories From Steps	Step-Based TDEE
3,000	122	2,202
5,000	204	2,284
8,000	327	2,406
10,000	408	2,488
12,000	490	2,569
15,000	612	2,692

Instead of jumping in 300-calorie blocks, the estimate moves smoothly with what you actually did. It also adjusts on its own: a 4,000-step rainy week and a 12,000-step vacation week get different numbers, while a fixed multiplier would treat them the same.

Two rules keep this honest:

Never stack steps on a higher multiplier. Using 1.55 and then adding step calories counts your walking twice.
Calorie estimates are still estimates. Treadmill consoles and watches all use models of their own. Our look at whether treadmill calories are accurate shows how far those numbers can drift.

The full walkthrough, including the double-counting trap and how to handle other workouts, is in how to calculate TDEE with steps. To convert your own step count for your exact weight, use the steps to calories calculator.

Using Your Mifflin-St Jeor Result for Weight Loss

Once you have a TDEE from the Mifflin-St Jeor equation, setting a calorie target is simple subtraction:

Mild deficit: TDEE minus 250 calories, roughly 0.5 lb per week
Moderate deficit: TDEE minus 500 calories, roughly 1 lb per week
Aggressive deficit: TDEE minus 750 to 1,000 calories, roughly 1.5 to 2 lb per week, best kept short

Avoid eating below your BMR for long stretches. It makes the diet harder to stick to and increases muscle loss. The calorie deficit calculator builds these targets for you and flags plans that go too low.

Then watch the scale for 2 to 4 weeks. If your weekly average is not moving at the rate you expected, your real TDEE is different from the prediction. Adjust by 100 to 200 calories and reassess. Your body's actual response always beats any formula.

Frequently Asked Questions

What is the Mifflin-St Jeor equation?

It is a formula for estimating resting metabolic rate, published in 1990. For men: 10 × weight (kg) + 6.25 × height (cm) − 5 × age + 5. For women: the same, but subtract 161 instead of adding 5. It is the BMR formula most dietitians and calorie calculators use by default.

Is Mifflin-St Jeor more accurate than Harris-Benedict?

For most adults, yes. A 2005 systematic review in the Journal of the American Dietetic Association found Mifflin-St Jeor was more likely than Harris-Benedict, Owen, or WHO/FAO/UNU to predict resting metabolic rate within 10% of measured values. Harris-Benedict tends to run about 5% high.

What is the Mifflin-St Jeor equation in pounds and inches?

Men: 4.536 × weight (lb) + 15.88 × height (in) − 5 × age + 5. Women: 4.536 × weight (lb) + 15.88 × height (in) − 5 × age − 161. These give the same result as the metric version.

Does the Mifflin-St Jeor equation give BMR or TDEE?

BMR (technically resting metabolic rate). To get TDEE, multiply the result by an activity factor between 1.2 and 1.9, or use the sedentary 1.2 factor and add calories from your daily steps.

Which BMR formula is best for athletes?

Katch-McArdle, as long as you have a reasonable body fat estimate. Because it is based on lean body mass, it accounts for extra muscle that the Mifflin-St Jeor equation would miss.

How accurate is the Mifflin-St Jeor equation for older adults?

Less certain than for younger adults. The 2005 review noted that older adults were underrepresented in the studies used to build and validate these equations. Treat the result as a starting point and adjust based on real weight trends.

Why is my BMR lower than I expected?

BMR is only the energy needed at complete rest, so it is usually much lower than people guess, often 1,300 to 1,800 calories for average adults. Most of your extra daily burn comes from movement, which is why your activity level or step count matters so much for TDEE.

Get Your Numbers and Put Them to Work

The Mifflin-St Jeor equation is the best general-purpose BMR formula available without a lab: simple, well-validated, and within 10% for most people. Calculate your BMR, multiply by 1.2, add your real daily steps instead of guessing an activity level, and adjust after a few weeks of real-world data.

Start with the BMR calculator to see Mifflin-St Jeor next to Harris-Benedict and Katch-McArdle, then use the TDEE calculator to turn it into a daily calorie target.

Ready to replace the activity guesswork with real data? Download Steps