The Mifflin-St Jeor Equation: Formula, Examples, and Limits
July 23, 2026
You want one number: how many calories your body actually burns. But every calculator online seems to spit out something different, and none of them explain their math.
Here's the thing. Most serious calorie calculators run on the same engine under the hood: the Mifflin-St Jeor equation.
It's the formula the Academy of Nutrition and Dietetics recommends for estimating resting metabolism in healthy adults. It's what our free calorie calculator uses too.
This article shows you the exact formula, why it beats the older alternatives, how to run the numbers yourself, and where it can be off.
The Mifflin-St Jeor Formula
The equation estimates your BMR: Basal Metabolic Rate, the calories you burn per day at complete rest.
It uses metric inputs, so convert first: pounds ÷ 2.2 = kg, and inches × 2.54 = cm.
For men:
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
For women:
BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
Notice the two versions differ only in the last term: +5 for men, −161 for women. That gap reflects average body-composition differences. Men typically carry more muscle at the same weight, and muscle burns more energy at rest than fat.
What each term tells you
| Term | Effect on BMR |
|---|---|
| 10 × weight (kg) | Every kg of body weight adds 10 calories/day |
| 6.25 × height (cm) | Taller bodies have more tissue to run |
| −5 × age | BMR drops about 5 calories/day per year of age |
| +5 / −161 | The sex adjustment |
The age term is worth pausing on. Your resting burn drifts down roughly 50 calories per decade by this formula. It's not dramatic, but it's one reason the eating habits of your 20s stop working in your 40s.
Why It's the Best-Validated Formula for Modern Adults
The Mifflin-St Jeor equation was published in 1990 by MD Mifflin, ST St Jeor, and colleagues. It was fitted to measurements of about 500 adults using indirect calorimetry (measuring actual oxygen consumption).
That publication date matters more than it sounds. The older Harris-Benedict equation dates to 1919. People measured in the 1910s were leaner and more physically active than people today. Formulas fit to those bodies tend to overestimate the resting burn of modern adults.
Mifflin-St Jeor was built on a modern population, including overweight subjects. In validation studies since, it has predicted measured BMR within 10% for more people than any other common formula. That's why the Academy of Nutrition and Dietetics names it the preferred equation for healthy adults.
In practice: for most people reading this, Harris-Benedict runs about 5% high. Mifflin-St Jeor lands closer to the truth.
Worked Examples
Let's calculate two real cases, step by step.
Example 1: a woman, 34, 150 lb, 5'4"
Convert first: 150 lb ≈ 68 kg, and 5'4" = 64 in ≈ 163 cm.
BMR = 10 × 68 + 6.25 × 163 − 5 × 34 − 161
BMR = 680 + 1,019 − 170 − 161 = 1,368 calories/day
That's her burn at complete rest. Nobody lies in bed all day, so her real daily burn is higher (more on that below).
Example 2: a man, 45, 210 lb, 6'0"
Convert: 210 lb ≈ 95 kg, and 6'0" = 72 in ≈ 183 cm.
BMR = 10 × 95 + 6.25 × 183 − 5 × 45 + 5
BMR = 950 + 1,144 − 225 + 5 = 1,874 calories/day
From BMR to your real daily target
BMR alone isn't your eating target. To get your Total Daily Energy Expenditure (TDEE), multiply BMR by an activity factor:
| Activity level | Multiplier |
|---|---|
| Sedentary (desk job, little exercise) | 1.2 |
| Lightly active (1-3 sessions/week) | 1.375 |
| Moderately active (3-5 sessions/week) | 1.55 |
| Very active (6-7 sessions/week) | 1.725 |
| Extremely active (physical job + training) | 1.9 |
Our example woman, lightly active: 1,368 × 1.375 ≈ 1,881 calories/day to maintain her weight.
Our example man, moderately active: 1,874 × 1.55 ≈ 2,905 calories/day.
To lose weight, you'd eat below that TDEE. A 550-calorie daily deficit works out to about 1 lb (0.5 kg) per week. That's because a pound of fat stores roughly 3,500 calories (~7,700 per kg).
Converting units and picking multipliers sounds tedious? The free calorie calculator runs the full Mifflin-St Jeor calculation and hands you a maintenance number plus a deficit target.
The Limitations (Read Before You Trust Any Number)
No formula reads your body directly. Mifflin-St Jeor is the best of the common options, but it's still an estimate with real limits.
It's accurate to about ±10%. For a true BMR of 1,500, the formula might say anywhere from roughly 1,350 to 1,650. That's a 300-calorie window. Good enough to start; not gospel.
It doesn't see body composition. Two people at 180 lb (82 kg) get the same result. That holds even if one is a lean lifter and the other carries little muscle. Muscular people burn more than the formula predicts; people with low muscle mass burn less.
It was validated on healthy adults. It's less reliable for athletes at extremes, older seniors, and people with thyroid conditions. Same for anyone at very high or very low body weight.
The activity multiplier is the weak link. The BMR part is decent science. The multiplier is a self-assessed guess, and most people guess high. When a calculated TDEE misses, the activity factor is usually why.
How to handle the error bar
Simple: treat the number as a hypothesis, then test it.
Eat at your calculated target for 2-3 weeks and track your weight. Losing at the expected pace? The estimate was good. Not moving? Your true burn is lower than predicted, so trim intake by 100-200 calories and reassess. Losing too fast, feeling wrecked? Add some back.
Your own scale data beats any formula. The equation just gives you an intelligent starting point instead of a blind guess.
FAQ
Is the Mifflin-St Jeor equation the same as a TDEE calculator?
It's the core of one. Mifflin-St Jeor gives you BMR (resting burn). A TDEE calculator multiplies that BMR by an activity factor to estimate your full daily burn. Most quality calorie calculators do both steps for you.
Which is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor, for most modern adults. Harris-Benedict was derived in 1919 from a leaner, more active population and tends to overestimate by around 5% today. Validation research consistently favors Mifflin-St Jeor for the general population.
Can I use the formula if I'm very muscular or very overweight?
You can, but expect more error. The formula only sees weight, height, age, and sex, not body composition. Very muscular people usually burn more than predicted. In both cases, use the result as a starting point and adjust based on 2-3 weeks of real-world results.
This is general information, not medical advice. If you have a medical condition, talk to your doctor or a registered dietitian before changing your diet.