How does Mifflin-St Jeor compare with Harris-Benedict?

The Harris-Benedict equation was originally developed in 1919 on a limited sample and revised in 1984. The Mifflin-St Jeor equation was derived in 1990 from a larger, more diverse, and more contemporary sample. Multiple validation studies, including a 2005 review by the American Dietetic Association, found that Mifflin-St Jeor often predicted resting metabolic rate more closely than several other common non-calorimetry equations.

What is the difference between BMR and RMR?

Basal Metabolic Rate (BMR) is measured under strict laboratory conditions — fasting, lying still, in a thermoneutral environment. Resting Metabolic Rate (RMR) is measured under less strict conditions and is typically 10-20% higher than BMR. The Mifflin-St Jeor equation technically estimates RMR, but the terms are commonly used interchangeably in practical nutrition planning.

Can I use Mifflin-St Jeor if I am very muscular or very obese?

For very muscular individuals, the Katch-McArdle or Cunningham equations may be more appropriate because they factor in lean body mass. For individuals with obesity (BMI > 35), all prediction equations lose accuracy, but Mifflin-St Jeor still performs better than most alternatives. In clinical settings for severe obesity, indirect calorimetry is preferred.

How do I use TDEE for weight loss?

A common starting deficit for weight loss is around 500-750 kcal below TDEE, which often corresponds to roughly 0.5-0.7 kg (1-1.5 lb) per week in many adults. Larger deficits may increase the risk of fatigue, muscle loss, or poor adherence, so individual tolerance and supervision matter.

How often should I recalculate my BMR?

Recalculate your BMR whenever your weight changes by 5 kg (11 lb) or more, after every birthday (since age is a factor), or every 3-6 months during an active diet or training program. Significant changes in activity level also warrant recalculation of your TDEE multiplier.

Does the Mifflin-St Jeor equation account for ethnicity?

No, the original Mifflin-St Jeor equation does not include an ethnicity variable. Some studies suggest it may overestimate BMR in Asian populations and underestimate it in African-American populations by 5-10%. If you fall into these groups, consider the result as a starting estimate and calibrate by tracking actual weight change.

What activity factor should I choose?

Sedentary (1.2) suits desk workers who rarely exercise. Lightly active (1.375) fits people who walk or do light exercise 1-3 days per week. Moderately active (1.55) applies to those exercising at moderate intensity 3-5 days per week. Very active (1.725) is for hard daily exercise, and extra active (1.9) is for athletes or people with extremely physical jobs. When in doubt, start with a lower factor and adjust upward.

Is the Mifflin-St Jeor equation suitable for children or teenagers?

The Mifflin-St Jeor equation was developed and validated primarily for adults aged 19-78. For children and adolescents, the Schofield equation or WHO/FAO/UNU equations are more appropriate, as they were specifically derived from pediatric data sets.

BMR Calculator — Mifflin-St Jeor Equation

Calculate your Basal Metabolic Rate using the Mifflin-St Jeor equation, a widely used BMR formula for the general population. Get TDEE estimates for standard activity levels.

Sex

Unit System

Height

Weight

Age

years

Basal Metabolic Rate (Mifflin-St Jeor)

1,748 kcal/day

7,314 kJ/day

Daily BMR

1,748 kcal

Energy at complete rest

Hourly Burn

72.8 kcal/hr

Resting rate

Weekly BMR

12,233 kcal

7-day resting total

Formula

Mifflin-St Jeor

1990 (Mifflin & St Jeor)

Estimated TDEE by Activity Level

Activity Level	Factor	kcal/day	kcal/week
Sedentary Little or no exercise, desk job	×1.2	2,097	14,679
Lightly Active Light exercise 1-3 days/week	×1.375	2,403	16,821
Moderately Active Moderate exercise 3-5 days/week	×1.55	2,709	18,963
Very Active Hard exercise 6-7 days/week	×1.725	3,014	21,098
Extra Active Very hard exercise, physical job	×1.9	3,320	23,240

Calorie Targets by Goal

Goal	Adjustment	Sedentary	Moderate
Aggressive Loss	−750 kcal	1,347	1,959
Moderate Loss	−500 kcal	1,597	2,209
Mild Loss	−250 kcal	1,847	2,459
Maintain	±0 kcal	2,097	2,709
Lean Gain	+250 kcal	2,347	2,959
Bulk	+500 kcal	2,597	3,209

Values are floored at 1,200 kcal/day for safety. Consult a professional before going below this threshold.

Calorie Ranges

BMR (at rest)1,748 kcal

Sedentary2,097 kcal

Lightly Active2,403 kcal

Moderately Active2,709 kcal

Very Active3,014 kcal

Extra Active3,320 kcal

This calculator provides estimates for educational purposes only. Results are not medical advice and should not be used for diagnosis or treatment. Consult a qualified healthcare professional for personal health assessments.

Planning notes, formulas, and examples

About the BMR Calculator — Mifflin-St Jeor Equation

The Mifflin-St Jeor equation, developed by MD Mifflin and ST St Jeor in 1990, is one of the most widely used basal metabolic rate (BMR) formulas for the general population. The American Dietetic Association (now the Academy of Nutrition and Dietetics) reviewed it favorably in 2005 for estimating resting energy expenditure in healthy adults. Compared with some older equations, Mifflin-St Jeor often performs well in contemporary adult samples, though it still remains an estimate rather than a direct measurement.

BMR represents the number of calories your body burns each day simply to maintain basic life-sustaining functions such as breathing, circulation, cell production, and temperature regulation. By multiplying your BMR by an activity factor, you obtain your Total Daily Energy Expenditure (TDEE), which is a practical estimate of total calories burned across a typical day.

This calculator implements the Mifflin-St Jeor equation with sex-specific formulas, supports both metric and imperial units, and provides TDEE estimates across five standard activity levels. The results are best treated as a starting point for calorie planning that can be adjusted based on your actual weight trend, appetite, training load, and day-to-day response.

When This Page Helps

The Mifflin-St Jeor equation is one of the most commonly used BMR estimates in nutrition practice. Studies suggest it predicts resting metabolic rate reasonably well for many healthy adults and often performs better than some older generalized equations. If you want a practical starting number to base calorie targets on, it is a reasonable first formula and it only requires sex, age, height, and weight.

How to Use the Inputs

Select your biological sex (male or female) as the formula uses different constants for each.
Choose your preferred unit system — metric (cm, kg) or imperial (ft/in, lb).
Enter your current height accurately, including fractional inches if using imperial.
Enter your current body weight as measured on a consistent scale.
Enter your age in years.
View your BMR result in kilocalories per day plus kilojoules.
Review the TDEE table to find the calorie level matching your typical activity.
Use the visual comparison bars to understand how activity level affects daily calorie needs.

Formula used

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

TDEE = BMR × Activity Factor
Sedentary: ×1.2 | Lightly Active: ×1.375 | Moderately Active: ×1.55 | Very Active: ×1.725 | Extra Active: ×1.9

Example Calculation

Result: 1,743 kcal/day

For a 30-year-old male who is 175 cm tall and weighs 78 kg: BMR = 10 × 78 + 6.25 × 175 − 5 × 30 + 5 = 780 + 1,093.75 − 150 + 5 = 1,728.75 ≈ 1,729 kcal/day. At a moderate activity level (×1.55), his TDEE would be approximately 2,680 kcal/day.

Tips & Best Practices

The Mifflin-St Jeor equation is generally used for healthy adults aged 19-78 and tends to perform best in people without very unusual body composition or major metabolic disruption.
Weigh yourself in the morning after using the bathroom and before eating for the most consistent input.
If you carry significant muscle mass, consider the Katch-McArdle equation instead, which uses lean body mass.
BMR naturally declines with age — roughly 1-2% per decade after age 20 — so recalculate periodically.
Your TDEE is an estimate; track your weight over 2-4 weeks and adjust calories by 250-500 kcal if weight isn't changing as expected.
The difference between sedentary and very active TDEE can be 700-1,200+ calories per day.
Body composition changes (gaining muscle, losing fat) may require recalculation even if scale weight stays the same.

The Science Behind Mifflin-St Jeor

MD Mifflin and ST St Jeor published their equation in the American Journal of Clinical Nutrition in 1990 after studying 498 healthy adults (247 female, 251 male) ranging from 19 to 78 years old. Their goal was to create a practical prediction equation for modern populations, since the widely used Harris-Benedict equation was derived from data collected in the early 1900s when average body compositions were quite different from today.

How It Compares to Other BMR Formulas

A 2005 evidence analysis by the American Dietetic Association compared five commonly used BMR prediction equations: Harris-Benedict (original and revised), Mifflin-St Jeor, Owen, and WHO/FAO/UNU. In that review, Mifflin-St Jeor performed well across both normal-weight and obese subjects. Harris-Benedict tended to overestimate in many individuals, while the Owen equation tended to underestimate.

Practical Applications for Nutrition Planning

Once you know your BMR and TDEE, you can sketch out a calorie plan aligned with your goals. For weight maintenance, many people start near their estimated TDEE. For fat loss, a moderate deficit is a common starting approach, while muscle-gain plans often start from a smaller calorie surplus. Macronutrient distribution also matters, and protein intake is often increased during calorie restriction to help preserve lean mass.

Limitations and When to Seek Professional Help

No prediction equation is perfect. Factors such as genetics, thyroid function, medications, menstrual cycle phase, and recent dieting history can all shift your actual metabolic rate away from predicted values. If you have been dieting for an extended period, your metabolic rate may be lower than predicted due to adaptive thermogenesis. In these cases, a registered dietitian or sports nutritionist using indirect calorimetry may provide a more precise estimate than any standard formula.

Sources & Methodology

Last updated: March 28, 2026

Methodology

This page applies the original Mifflin-St Jeor 1990 equations, using sex-specific constants together with the entered weight, height, and age to estimate resting energy expenditure in kilocalories per day. It then multiplies that BMR estimate by the selected activity factor to show practical TDEE planning ranges.

The result is a prediction equation, not a direct metabolic measurement. The activity table uses conventional lifestyle multipliers as worksheet assumptions, so the output should be treated as a starting estimate and then calibrated against real intake, weight, and training trends.

Sources

A new predictive equation for resting energy expenditure in healthy individuals (PubMed / American Journal of Clinical Nutrition) — Original Mifflin-St Jeor 1990 equation.
Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review (PubMed / Journal of the American Dietetic Association) — Review describing practical accuracy of the Mifflin-St Jeor and other common equations.

Frequently Asked Questions

The Harris-Benedict equation was originally developed in 1919 on a limited sample and revised in 1984. The Mifflin-St Jeor equation was derived in 1990 from a larger, more diverse, and more contemporary sample. Multiple validation studies, including a 2005 review by the American Dietetic Association, found that Mifflin-St Jeor often predicted resting metabolic rate more closely than several other common non-calorimetry equations.
Sedentary (1.2) suits desk workers who rarely exercise. Lightly active (1.375) fits people who walk or do light exercise 1-3 days per week. Moderately active (1.55) applies to those exercising at moderate intensity 3-5 days per week. Very active (1.725) is for hard daily exercise, and extra active (1.9) is for athletes or people with extremely physical jobs. When in doubt, start with a lower factor and adjust upward.