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

Quick Answer: For the general adult population, Mifflin-St Jeor is more accurate (±10% error) than Harris-Benedict. The original Harris-Benedict (1919) tends to overestimate BMR by 5–15% for modern sedentary adults. Use Mifflin-St Jeor as your default; use Katch-McArdle when you know your body fat percentage.

The two formulas, side by side

Mifflin-St Jeor (1990)

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

Harris-Benedict (revised 1984)

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)

Both predict basal metabolic rate from age, sex, height, and weight. The difference is in the coefficients — and those coefficients come from the populations they were derived in.

Origin and validation

Harris-Benedict (1919, revised 1984)

Developed by James Harris and Francis Benedict at the Carnegie Institution. The original sample was 239 mostly male, mostly young, mostly lean American adults measured by direct calorimetry over a few weeks. It was the first formula widely used in medicine and survived as the dietetic standard for decades.

The 1984 Roza-Shizgal revision recalibrated the coefficients using more recent data, but the underlying form (and the original sample's bias toward lean, young men) remained.

Mifflin-St Jeor (1990)

M.D. Mifflin, S.T. St Jeor, and colleagues developed this formula from a study of 498 healthy adults across a wider weight range, including obese individuals. It was specifically built to better predict BMR in modern populations who, on average, carry more body fat than the 1919 sample.

A 2005 systematic review in the Journal of the American Dietetic Association compared four BMR equations against indirect calorimetry. Mifflin-St Jeor had the smallest mean error (–1 kcal in non-obese, +1.5% in obese). Harris-Benedict overestimated BMR in both groups, with errors of +5 to +15%.

Where the formulas differ in practice

In every typical adult profile, Harris-Benedict predicts a slightly higher BMR than Mifflin-St Jeor. The gap widens for older, heavier, sedentary adults — exactly the population most likely to be on a weight-loss plan.

Real-world impact: the deficit example

Suppose you're a sedentary woman aiming to cut at –20% below TDEE:

Using Mifflin-St Jeor:

• BMR: 1,395
• TDEE (×1.2): 1,675
• Cutting target (–20%): 1,340 kcal/day

Using Harris-Benedict:

• BMR: 1,485
• TDEE (×1.2): 1,780
• Cutting target (–20%): 1,425 kcal/day

The Harris-Benedict cut target is 85 kcal/day higher. Over 8 weeks, that gap could translate to ~1.5 lb of missed fat loss if Harris-Benedict overestimated your true TDEE.

When does Harris-Benedict still get used?

Three places:

1. Older clinical references. Many published nutrition books still print Harris-Benedict as the primary formula. It's not wrong, just less accurate on average.
2. Cross-checking. If both formulas land within 50 kcal of each other, your prediction is well-anchored.
3. Hospital nutrition support. Some clinical protocols specify Harris-Benedict because it has a long validation track record. Newer protocols increasingly favor Mifflin-St Jeor or direct calorimetry.

For everyday weight management, Mifflin-St Jeor is the right default.

When neither formula is best: enter Katch-McArdle

Katch-McArdle: BMR = 370 + (21.6 × LBM in kg)

LBM = lean body mass = total weight × (1 − body fat fraction).

Because Katch-McArdle uses lean mass directly, it sidesteps the body-composition problem that breaks both Mifflin-St Jeor and Harris-Benedict at the extremes.

Use Katch-McArdle when:

• You know your body fat percentage (DEXA, Navy method, BodPod)
• You're notably lean for your weight (athletic, low body fat)
• You're notably high in body fat (Mifflin-St Jeor will overestimate BMR for very high BF%)

For a 175-lb man at 10% body fat (LBM = 71.5 kg):

• Mifflin-St Jeor BMR (sedentary): 1,755 kcal
• Katch-McArdle BMR: 1,914 kcal
• Difference: +159 kcal/day — significant for a lean athlete in a deficit

For a 175-lb man at 30% body fat (LBM = 55.6 kg):

• Mifflin-St Jeor BMR: 1,755 kcal
• Katch-McArdle BMR: 1,571 kcal
• Difference: −184 kcal/day — Mifflin-St Jeor is overestimating

Decision tree: which formula to use

Do you know your body fat %?
├── Yes → Use Katch-McArdle (most accurate for body-comp outliers)
└── No
    ├── Is your body composition typical for your demographic?
    │   ├── Yes → Use Mifflin-St Jeor (best for general population)
    │   └── No (very lean or very high BF%) → Get a body fat estimate (Navy method works) and switch to Katch-McArdle

The BMR calculator on this page runs all three formulas at once and recommends the best fit based on your inputs.

Other BMR formulas (quick reference)

Bottom line

• Default: Mifflin-St Jeor. It's the most accurate for adults across age, sex, and weight ranges.
• If you have body fat %: Katch-McArdle. More accurate for lean athletes and high-body-fat individuals.
• Cross-check tool: Harris-Benedict. Useful when you want a second opinion, but don't use it as the primary basis for your calorie target.

Try all three in the BMR calculator — see how your numbers compare side-by-side. The full BMR guide walks through factors that affect BMR beyond what any formula can predict.