Mifflin-St Jeor vs. Harris-Benedict: Which TDEE Calorie Formula is Actually More Accurate?
If you have ever searched for a TDEE calculator, you have probably seen references to two competing formulas without a clear explanation of which one to use or why it matters. Here is the straightforward breakdown.
What TDEE Actually Means
Total Daily Energy Expenditure is the total number of calories your body burns in a 24-hour period. It includes your resting metabolic rate, the energy cost of digesting food, and the calories burned through physical activity. Knowing your TDEE gives you the only number that actually matters for weight management, the baseline above or below which calories produce muscle gain or fat loss.
The Harris-Benedict Equation
James Arthur Harris and Francis Gano Benedict developed the original formula in 1919, revised in 1984 by Roza and Shizgal. The 1984 version is what most older calculators use:
Harris-Benedict (Revised 1984):
- Men: 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) - (5.677 x age in years)
- Women: 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) - (4.330 x age in years)
The Mifflin-St Jeor Equation
Mark D. Mifflin and Sachiko T. St Jeor published a revised formula in 1990 after testing it against measured resting metabolic rates in 498 participants. The American Dietetic Association reviewed the research and determined that the Mifflin-St Jeor equation is the more accurate predictor for most people:
Mifflin-St Jeor:
- Men: (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5
- Women: (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161
Which Formula Is More Accurate?
Multiple independent studies have compared both formulas against indirect calorimetry, the scientific gold standard for measuring actual metabolic rate. The consistent finding is that Mifflin-St Jeor predicts measured BMR within 10% in the majority of subjects, outperforming Harris-Benedict for most body types and activity levels.
Harris-Benedict tends to overestimate BMR by about 5% on average, which means people using it may end up eating slightly more than they need for a true deficit.
Calculate My TDEE
When Harris-Benedict Might Perform Better
For older individuals and people who are significantly overweight or underweight, neither formula is especially precise. Some research suggests Harris-Benedict performs marginally better for elderly populations. At extreme ends of the body composition spectrum, both formulas are approximations and tracking actual intake against measured outcomes over several weeks remains the only reliable method.
The Activity Multiplier Matters Too
Both formulas calculate your Basal Metabolic Rate, what you burn at rest. To get TDEE, you multiply BMR by an activity factor ranging from 1.2 for sedentary to 1.9 for extremely active. This multiplier is estimated, not measured, and it introduces more variance than the formula choice itself. Most people underestimate their activity level, which is why their calculated TDEE ends up higher than what they actually need.
Start with the Mifflin-St Jeor calculated value, eat at that level for two weeks, and adjust based on actual observed changes in weight. Real-world feedback is always more accurate than any formula.