Harris-Benedict vs. Mifflin-St Jeor: What the Research Actually Shows

Medically reviewed for accuracy against peer-reviewed nutrition research. Last updated: August 2026.

If you've compared calorie calculators online, you've probably noticed the numbers don't always match. Plug the same age, weight, and height into two different tools, and one might hand you a Harris-Benedict result while the other quietly runs Mifflin-St Jeor in the background — and the two totals can differ by 50 to 150 calories a day. That gap isn't a bug. It's the result of two different research teams, working seven decades apart, building two different formulas from two different groups of people.

This guide breaks down what actually separates Harris-Benedict from Mifflin-St Jeor, what the research says about which one predicts your metabolism more accurately, and — importantly — where that answer changes depending on your age and body composition.

The Short Answer

For most healthy adults, Mifflin-St Jeor is the more accurate default. It was built in 1990 using a larger, more representative sample than Harris-Benedict's original 1919 dataset, and multiple validation studies have found it predicts resting metabolic rate closer to lab-measured values on average.

But "more accurate on average" isn't the same as "always right for you" — and recent research on older adults complicates the usual advice. Here's the comparison at a glance:

How Each Formula Actually Works

Both formulas ask for the same four numbers — weight, height, age, and sex — and both spit out an estimated Basal Metabolic Rate (BMR) in calories per day. The difference is entirely in the coefficients.

The Mifflin-St Jeor Formula

Developed by Dr. Mark Mifflin and Dr. Sachiko St Jeor and published in the American Journal of Clinical Nutrition in 1990.

For men:

BMR = (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years) + 5

For women:

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

The Harris-Benedict Formula (Revised)

Originally published in 1919, then revised in 1984 using updated data. Always use the revised version — the original consistently overestimates BMR by 5–15% for modern populations.

For men:

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

For women:

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

Once you have a BMR from either formula, the next step is the same: multiply by an activity factor to get your TDEE (Total Daily Energy Expenditure). Neither formula changes how that second step works.

What the Research Actually Shows

This is where most comparison articles stop at "Mifflin-St Jeor is more accurate" and move on. The research is more layered than that, and the layers matter if you're actually trying to hit a calorie target.

At a group level, Mifflin-St Jeor edges out Harris-Benedict. The most-cited reference here is a 2005 systematic review by Frankenfield, Roth-Yousey, and Compher in the Journal of the American Dietetic Association.

The review found Mifflin-St Jeor was more likely than older equations, including Harris-Benedict, to predict resting metabolic rate within 10% of values measured by indirect calorimetry — the lab-standard method that measures metabolism directly from oxygen consumption.

But at an individual level, both formulas have real error margins. A 2008 study published in the Indian Journal of Medical Sciences compared both equations against indirect calorimetry in 60 hospitalized patients.

The study found no statistically significant difference between them as a group — but wide limits of agreement for both formulas individually, meaning either one could be off by a clinically meaningful amount for any single person, regardless of which formula was used. The researchers' conclusion was blunt: Harris-Benedict works fine at a group level, but neither formula should be trusted precisely for one specific individual.

Body weight changes the accuracy, too. A 2013 study in Clinical Nutrition tracked 337 ambulatory adults and found Mifflin-St Jeor was accurate (within 10% of measured RMR) for about 82% of participants overall.

That accuracy rate dropped to roughly 75% in people with obesity, compared to about 87% in non-obese participants. The formula doesn't fail in higher-weight individuals, but its margin for error widens.

And here's the finding almost no other comparison article mentions: the 2005 systematic review flagged older adults as underrepresented in the original validation research for both formulas — meaning nobody had tested, with much confidence, which formula actually works better once you're past 60.

A 2025 undergraduate research poster from Miami University (Hudak, mentored by Dr. Kyle Timmerman) set out to close that exact gap, measuring resting metabolic rate via indirect calorimetry in 48 adults ages 58 to 78 (average age 64).

The result ran counter to the usual advice: Harris-Benedict correlated more closely with measured RMR (r = 0.445) than Mifflin-St Jeor did (r = 0.39) in this older-adult group, even though both formulas slightly overestimated the measured rate. It's a single, relatively small study — not enough to overturn the broader research on its own — but it's a direct, recent answer to a gap the field had openly acknowledged, and it suggests the "Mifflin is always more accurate" rule of thumb may not hold as cleanly for older adults.

Worked Example: Same Person, Two Formulas

Take a 45-year-old woman who weighs 70 kg and is 165 cm tall.

Mifflin-St Jeor:

BMR = (10 × 70) + (6.25 × 165) − (5 × 45) − 161
BMR = 700 + 1,031.25 − 225 − 161
BMR = 1,345 calories/day

Harris-Benedict (revised):

BMR = 447.593 + (9.247 × 70) + (3.098 × 165) − (4.330 × 45)
BMR = 447.593 + 647.29 + 511.17 − 194.85
BMR = 1,411 calories/day

The two formulas land about 66 calories apart for this profile. That's a modest gap on its own, but once it's multiplied by an activity factor to calculate TDEE — and then tracked across weeks of a calorie deficit or surplus — a consistent 66-calorie difference adds up to roughly 460 calories a week, or close to two extra days of unaccounted intake over a month.

Want your own numbers instead of doing the math by hand? Our Mifflin-St Jeor calculator runs the formula for you in seconds.

Does Body Type or Age Change Which Formula Wins?

Based on what the research actually shows, the honest answer is: sometimes, yes.

• Average-weight adults under 60: Mifflin-St Jeor has the stronger overall track record and is the reasonable default.
• Adults with obesity: Mifflin-St Jeor is still the better-supported choice, but expect a wider margin of error than in normal-weight individuals — treat the result as a rougher estimate and lean more heavily on 2–3 weeks of real-world tracking to fine-tune it.
• Adults over 60: The evidence here is thinner and more mixed than most articles let on. The 2025 Miami University data suggests Harris-Benedict may track measured RMR at least as well, if not better, in this age group — worth knowing if your Mifflin-St Jeor number feels consistently off.
• Athletes with a known body fat percentage: Neither formula accounts for lean body mass directly. If you've had a DEXA scan or similar measurement, the Katch-McArdle formula is generally a better fit than either Mifflin-St Jeor or Harris-Benedict.

Which One Should You Actually Use?

For the vast majority of people reading this, Mifflin-St Jeor remains the right starting point — it has the broadest and most consistent research support across the general adult population, and it's the formula recommended by the Academy of Nutrition and Dietetics for healthy adults. Our BMR calculator uses it by default for exactly that reason.

That said, treat any BMR number — from either formula — as a starting estimate, not a locked-in fact. Eat at your calculated TDEE for two to three weeks, watch what actually happens to your weight, and adjust from there. Real-world tracking will always out-perform any formula, because it's measuring you specifically instead of a population average.

Frequently Asked Questions

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

Not always. On average, across the general adult population, yes — but individual-level accuracy varies for both formulas, and at least one recent study on older adults found Harris-Benedict correlated more closely with measured metabolic rate in that specific age group.

How different are the results between the two formulas?

Usually 50–150 calories per day for the same person. The gap tends to widen for people at the extremes of body weight or age, where both formulas' error margins increase.

Which formula should I use if I'm over 60?

Mifflin-St Jeor is still a reasonable starting point, but don't be surprised if it runs a bit high or low. Given the limited and mixed research specific to older adults, cross-checking against Harris-Benedict and adjusting based on 2–3 weeks of real-world weight tracking is a sensible approach.

Does body weight affect which formula is more accurate?

Yes. Mifflin-St Jeor's accuracy is highest in non-obese adults (roughly 87% of people within 10% of measured values in one 2013 study) and somewhat lower in adults with obesity (roughly 75% in the same study) — still the better-supported option, just with a wider margin.

Should I just use both formulas and average them?

It's a reasonable cross-check rather than a rule. If both formulas land within 100–150 calories of each other, starting from the lower number is a sensible way to avoid overestimating your calorie needs.