Mifflin-St Jeor vs Harris-Benedict: Which Calorie Formula Is More Accurate?

If you've ever used a calorie calculator online, it almost certainly used one of two formulas: Mifflin-St Jeor or Harris-Benedict. They're both trying to answer the same question — how many calories does your body burn at rest? — but they were developed decades apart, and their accuracy differs meaningfully.

Here's what the research actually says.

What are these formulas calculating?

Both formulas estimate your Basal Metabolic Rate (BMR) — the number of calories your body needs to maintain basic functions (breathing, circulation, cell repair) if you did absolutely nothing all day.

BMR is the foundation of TDEE (Total Daily Energy Expenditure) — your actual daily calorie needs once activity is factored in.

Getting your BMR right matters because even a 10% error compounds over time. If your calculator overestimates your BMR by 200 calories and you eat to that number, you'd gain roughly one kilogram of fat every 5 weeks without realising it.

The Harris-Benedict Equation (1919, revised 1984)

The original Harris-Benedict equation was published in 1919 — over 100 years ago — based on data from 239 subjects. It was revised by Roza and Shizgal in 1984.

Revised Harris-Benedict formulas:

Men:
BMR = 88.362 + (13.397 × weight in kg) + (4.799 × height in cm) − (5.677 × age)

Women:
BMR = 447.593 + (9.247 × weight in kg) + (3.098 × height in cm) − (4.330 × age)

The 1919 dataset was small, not representative of modern populations, and collected before contemporary body composition research. The 1984 revision improved it somewhat, but the underlying dataset remained limited.

The Mifflin-St Jeor Equation (1990)

The Mifflin-St Jeor equation was published in 1990 by Mark D. Mifflin and Sachiko T. St Jeor, based on data from 498 subjects — more than twice the Harris-Benedict dataset — and collected under controlled metabolic conditions.

Mifflin-St Jeor formulas:

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

The formula is simpler, more recent, and was derived from a more rigorous methodology.

What does the research say about accuracy?

This is where the comparison becomes clear.

A landmark study published in the Journal of the American Dietetic Association (Frankenfield et al., 2005) compared four common BMR equations against indirect calorimetry (the gold standard for measuring actual metabolic rate) in 199 subjects.

The results:

• Mifflin-St Jeor: Accurate within 10% in 82% of subjects — the best performance of any formula tested
• Harris-Benedict (revised): Accurate within 10% in 68% of subjects
• Harris-Benedict (original 1919): Consistently overestimated BMR by 5–15%

The conclusion was unambiguous: Mifflin-St Jeor is the most accurate of the standard prediction equations for estimating BMR in healthy, non-obese adults.

This is why the Academy of Nutrition and Dietetics and most clinical guidelines now recommend Mifflin-St Jeor as the preferred equation.

Where Harris-Benedict still gets used

Despite being less accurate, Harris-Benedict remains common because:

1. It was the standard for decades and many tools haven't been updated
2. Both formulas are close enough for rough estimates that the difference doesn't matter to most users
3. Some software and apps were built before the research clearly favoured Mifflin-St Jeor

If a calorie calculator doesn't specify which formula it uses, there's a reasonable chance it's still using Harris-Benedict — or a proprietary version that's not validated at all.

The activity multiplier problem

Both formulas require multiplying your BMR by an activity factor to get TDEE. The standard multipliers used by most calculators:

These multipliers are the weakest part of any TDEE estimate. Most people overestimate their activity level, which leads to overestimating their calorie needs. Research suggests the "moderately active" category is where most people who think they're "very active" actually fall.

A good calculator lets you specify your actual exercise frequency and type, rather than asking you to self-select a vague category.

Which formula should you use?

Use Mifflin-St Jeor. The evidence is consistent and the formula is recommended by clinical dietetics organisations. There's no scenario where Harris-Benedict is more accurate for a healthy adult.

That said, both formulas are estimates. Your actual BMR can vary by ±10% from any prediction formula due to individual differences in body composition, thyroid function, and genetics. The most accurate way to know your true BMR is indirect calorimetry in a lab setting.

For practical purposes, use Mifflin-St Jeor as your starting point, track your actual weight change over 2–3 weeks at a given calorie intake, and adjust from there.

What about other formulas?

• Katch-McArdle: Uses lean body mass instead of total body weight, which makes it more accurate if you know your body fat percentage. Good option if you have a DEXA scan or reliable body composition measurement.
• Schofield: Used by some international health organisations; similar accuracy to Mifflin-St Jeor but less widely validated in modern Western populations.
• WHO/FAO/UNU: Population-level formula used for public health work; less precise for individuals.

For most people, Mifflin-St Jeor is the best balance of accuracy and accessibility.

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References:
Mifflin MD, St Jeor ST, et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990.
Frankenfield D, Roth-Yousey L, Compher C. Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults. J Am Diet Assoc. 2005.
Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr. 1984.