BMR Calculator - Basal Metabolic Rate (Mifflin-St Jeor Equation)

Find your exact Basal Metabolic Rate using the Mifflin-St Jeor equation and see calorie targets for every goal.

Unit System

Weight75

30 kg200 kg

Height175

120 cm220 cm

Age30

yrs

1899

Gender

Activity Level

Compare Mifflin-St Jeor (1990) and Harris-Benedict (1984) BMR estimates for your measurements.

BMR (Mifflin-St Jeor)

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TDEE (Maintenance)

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Activity Multiplier

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Fat Loss (-500 kcal)

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Lean Bulk (+400 kcal)

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Calorie Targets by Goal

Mifflin-St Jeor BMR

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Harris-Benedict BMR

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Difference

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Assessment

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🔥 What is the Mifflin-St Jeor BMR Equation?

Basal Metabolic Rate (BMR) is the number of calories your body needs to sustain essential physiological functions while at complete rest: breathing, blood circulation, cell repair, protein synthesis, temperature regulation, and continuous organ activity. BMR represents the minimum energy expenditure to keep you alive and makes up roughly 60 to 75 percent of your Total Daily Energy Expenditure (TDEE).

The Mifflin-St Jeor equation is the most widely validated formula for estimating BMR in the general adult population. Developed by Mifflin, St Jeor, and colleagues in 1990 and published in the American Journal of Clinical Nutrition, it was built on a sample of 498 healthy adults and has since been independently validated across multiple study populations. A landmark 2005 comparison study in the Journal of the American Dietetic Association found it predicted measured resting metabolic rate within 10% for 82% of subjects, outperforming the Harris-Benedict equation (72% accuracy) and making it the formula recommended by the Academy of Nutrition and Dietetics.

Once you have your BMR, you multiply it by an activity factor to get your TDEE. This is the number that drives all practical nutrition decisions: eat at TDEE to maintain weight, below TDEE to lose fat, and above TDEE to gain muscle. Without an accurate BMR baseline, every calorie target is guesswork. Common uses include setting a daily calorie budget for fat loss, calculating protein requirements relative to total energy, adjusting intake during training cycles, and comparing dietary strategies (deficit vs. surplus) in quantitative terms.

It is worth noting what BMR does not capture. It does not account for body composition directly (two people with the same weight but different muscle-to-fat ratios will have different actual metabolic rates). It does not adjust for thyroid disorders, hormonal imbalances, or medications that affect metabolism. And it is an estimate, not a measurement. For most healthy adults, however, Mifflin-St Jeor provides an excellent starting-point estimate that can be refined through 2 to 3 weeks of real-world calorie tracking and weight monitoring.

📐 Formula

Men: BMR = (10 × W) + (6.25 × H) − (5 × A) + 5

Women: BMR = (10 × W) + (6.25 × H) − (5 × A) − 161

W = Body weight in kilograms (kg)

H = Height in centimetres (cm)

A = Age in years

Sex constant = +5 for men, −161 for women

TDEE = BMR × Activity Factor (1.2 to 1.9)

Example (male, 75 kg, 175 cm, age 30): BMR = (10×75) + (6.25×175) − (5×30) + 5 = 750 + 1,093.75 − 150 + 5 = 1,699 kcal

Harris-Benedict (1984 revised) for comparison:

Men: BMR = 88.362 + (13.397 × W) + (4.799 × H) − (5.677 × A)

Women: BMR = 447.593 + (9.247 × W) + (3.098 × H) − (4.330 × A)

📖 How to Use This Calculator

Steps

Select your unit system - choose Metric (kg/cm) or Imperial (lbs/in) from the dropdown. The sliders adjust their ranges automatically when you switch units.

Enter weight, height, and age - type values directly or drag the sliders. The display label above each slider updates in real time.

Select your gender - Male or Female. The Mifflin-St Jeor formula applies a different sex constant (+5 or -161) to account for average differences in muscle mass between men and women.

Choose your activity level (BMR and Goals mode) - select the level that honestly describes your typical week. Most desk workers with 3 to 4 gym sessions per week are Lightly Active, not Moderately Active.

Click Calculate - see your BMR, TDEE, and the 6-goal calorie table. Switch to Compare Formulas tab to view Mifflin-St Jeor and Harris-Benedict results side by side for the same inputs.

💡 Example Calculations

Example 1 - Average Man, Moderately Active

Male, 75 kg, 175 cm, age 30, moderately active (gym 4 times per week)

Mifflin-St Jeor BMR = (10×75) + (6.25×175) − (5×30) + 5 = 750 + 1,093.75 − 150 + 5 = 1,699 kcal.

Moderately Active multiplier = 1.55. TDEE = 1,699 × 1.55 = 2,633 kcal.

Fat loss target = 2,633 − 500 = 2,133 kcal. Lean bulk target = 2,633 + 400 = 3,033 kcal.

BMR = 1,699 kcal | TDEE = 2,633 kcal/day

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Example 2 - Woman, Lightly Active

Female, 62 kg, 163 cm, age 28, lightly active (daily walks plus gym 2 times per week)

Mifflin-St Jeor BMR = (10×62) + (6.25×163) − (5×28) − 161 = 620 + 1,018.75 − 140 − 161 = 1,338 kcal.

Lightly Active multiplier = 1.375. TDEE = 1,338 × 1.375 = 1,840 kcal.

Fat loss target = 1,840 − 500 = 1,340 kcal. Since this is above the 1,200 kcal minimum for women, it is safe to sustain.

BMR = 1,338 kcal | TDEE = 1,840 kcal/day

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Example 3 - Comparing Mifflin-St Jeor vs Harris-Benedict

Female, 70 kg, 168 cm, age 45 - formula comparison

Mifflin-St Jeor BMR = (10×70) + (6.25×168) − (5×45) − 161 = 700 + 1,050 − 225 − 161 = 1,364 kcal.

Harris-Benedict BMR = 447.593 + (9.247×70) + (3.098×168) − (4.330×45) = 447.593 + 647.29 + 520.46 − 194.85 = 1,420 kcal.

Difference = 1,420 − 1,364 = 56 kcal. Harris-Benedict gives a higher estimate by 56 kcal for this individual.

Mifflin = 1,364 kcal | Harris-Benedict = 1,420 kcal | Difference = 56 kcal

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❓ Frequently Asked Questions

What is the Mifflin-St Jeor equation and why is it the recommended BMR formula?+

The Mifflin-St Jeor equation (1990) calculates Basal Metabolic Rate from weight, height, age, and sex. It is recommended by the Academy of Nutrition and Dietetics because it predicts measured resting metabolic rate within 10% for approximately 82% of adults, versus 72% for the older Harris-Benedict equation. It was developed on a sample of 498 healthy adults using multiple linear regression and has since been validated across additional populations.

How do I calculate BMR using the Mifflin-St Jeor formula manually?+

For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) + 5. For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age) - 161. Example for a 35-year-old man at 80 kg and 180 cm: BMR = (10 x 80) + (6.25 x 180) - (5 x 35) + 5 = 800 + 1,125 - 175 + 5 = 1,755 kcal per day.

What is the difference between Mifflin-St Jeor and Harris-Benedict BMR estimates?+

Both formulas estimate BMR from the same four inputs (weight, height, age, sex) but use different regression coefficients derived from different study populations and decades. On average, Mifflin-St Jeor yields BMR estimates 5 to 10% lower than Harris-Benedict for the same inputs in most adults. Research consistently shows Mifflin-St Jeor is more accurate against measured values, particularly for overweight and obese individuals where Harris-Benedict tends to overestimate.

What is a normal BMR for a 30-year-old man?+

For an average 30-year-old man (75 kg, 175 cm), the Mifflin-St Jeor formula produces a BMR of approximately 1,699 kcal per day. This accounts for breathing, circulation, organ function, cell repair, and temperature regulation while at complete rest. BMR typically ranges from 1,500 to 2,100 kcal for adult men depending on body size.

What is a normal BMR for a 30-year-old woman using the Mifflin-St Jeor equation?+

For an average 30-year-old woman (62 kg, 163 cm), Mifflin-St Jeor gives a BMR of approximately 1,338 kcal per day. Women have lower BMR than men at similar body weight primarily due to proportionally lower skeletal muscle mass. BMR for adult women typically ranges from 1,200 to 1,700 kcal per day.

How does BMR change with age according to the Mifflin-St Jeor formula?+

The Mifflin-St Jeor equation reduces BMR by 5 kcal for each year of age (the -5 x age term). A 60-year-old at the same weight and height as a 30-year-old has a formula-predicted BMR that is 150 kcal per day lower. In practice this reflects the gradual loss of lean muscle mass (sarcopenia) that begins in the 30s. Resistance training preserves lean mass and is the most effective way to counteract age-related BMR decline.

How do I use my BMR to set a calorie target for fat loss?+

First multiply your BMR by the appropriate activity factor to get TDEE. Then subtract 300 to 500 kcal from TDEE to create a moderate daily deficit. A 500 kcal/day deficit produces approximately 0.5 kg of fat loss per week. Never drop below 1,200 kcal per day (women) or 1,500 kcal per day (men) without medical supervision. Reassess your TDEE every 4 to 6 weeks as weight changes.

Is the Mifflin-St Jeor formula accurate for people with obesity?+

Mifflin-St Jeor performs better for overweight individuals than Harris-Benedict and is the preferred formula for people with obesity per most nutrition guidelines. It may still overestimate BMR in people with very high body fat percentage because excess fat tissue is metabolically less active than lean tissue, but the formula does not distinguish between them. For BMI over 35, the Katch-McArdle formula (using lean body mass) may be more precise if body composition data is available.

What activity level multiplier should I choose for TDEE calculation?+

Sedentary (1.2x): office job with little movement and no formal exercise. Lightly Active (1.375x): office job plus 1 to 3 days per week of gym or cardio. Moderately Active (1.55x): office job plus 3 to 5 days of moderate training, or an active job. Very Active (1.725x): hard exercise 6 to 7 days per week or a physically demanding job. Extra Active (1.9x): very hard daily training plus physical labor, or twice-daily training. Most gym-goers overestimate their level by one category.

Does BMR change when I lose weight?+

Yes. As body weight decreases, BMR decreases because there is less body mass requiring energy to maintain. Losing 5 kg typically reduces BMR by 50 to 100 kcal per day. This is called metabolic adaptation and is why calorie targets must be recalculated every 4 to 6 weeks during a sustained fat-loss phase. Preserving lean muscle through adequate protein intake and resistance training minimizes the BMR drop per kg of weight lost.

What is the difference between BMR and TDEE?+

BMR is the calories burned at complete rest to sustain basic physiological functions. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor that accounts for all daily movement: exercise, walking, household activity, work tasks, and non-exercise fidgeting. TDEE is the actionable number for nutrition planning. Eating at TDEE maintains weight; eating below TDEE creates a deficit for fat loss; eating above TDEE supports muscle gain.

Why does the formula give different results for men and women at the same weight?+

The sex constant (+5 for men, -161 for women) captures the average 166 kcal per day difference in BMR between males and females at the same weight, height, and age. This difference exists because men typically carry proportionally more skeletal muscle mass and less adipose tissue than women. Muscle tissue burns approximately 13 kcal per kg per day at rest, versus 4.5 kcal per kg for fat tissue. Higher muscle mass directly translates to a higher resting metabolic rate.

🔗 Related Calculators

What is the Mifflin-St Jeor equation for BMR?

The Mifflin-St Jeor equation (1990) calculates BMR as follows. For men: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) + 5. For women: BMR = (10 x weight in kg) + (6.25 x height in cm) - (5 x age in years) - 161. The only difference between the formulas is the sex constant: +5 for men and -161 for women.

How accurate is the Mifflin-St Jeor BMR formula?

A 2005 study in the Journal of the American Dietetic Association found that the Mifflin-St Jeor equation predicted resting metabolic rate within 10% for approximately 82% of subjects, compared to 72% for the Harris-Benedict equation. It performs best for non-obese adults aged 18 to 65. For individuals with very high or very low body fat percentages, actual metabolic rate may deviate by 10 to 20% from the formula estimate.

What is the difference between Mifflin-St Jeor and Harris-Benedict BMR?

Both formulas estimate Basal Metabolic Rate from weight, height, age, and sex, but they use different coefficients. Mifflin-St Jeor (1990) was developed on a more recent population sample and uses simpler linear coefficients. Harris-Benedict (revised 1984) uses different base constants and weight coefficients. On average, Mifflin-St Jeor yields slightly lower BMR estimates than Harris-Benedict for most adults. Most nutrition organizations now recommend Mifflin-St Jeor as the default.

What is a normal BMR for a 30-year-old man using Mifflin-St Jeor?

For an average 30-year-old man (75 kg, 175 cm), the Mifflin-St Jeor formula gives a BMR of approximately 1,699 kcal per day. At a moderately active level (1.55x multiplier), his TDEE would be about 2,633 kcal per day. BMR typically ranges from 1,500 to 2,100 kcal for adult men, depending on body size.

What is a normal BMR for a 30-year-old woman using Mifflin-St Jeor?

For an average 30-year-old woman (62 kg, 163 cm), the Mifflin-St Jeor formula gives a BMR of approximately 1,338 kcal per day. At a lightly active level (1.375x), her TDEE would be about 1,840 kcal. Women consistently have lower BMR than men at similar body weight because they carry proportionally less lean muscle mass.

How do I calculate TDEE from BMR using Mifflin-St Jeor?

Multiply your Mifflin-St Jeor BMR by the activity factor that matches your typical week. Sedentary (little or no exercise): 1.2x. Lightly Active (1 to 3 days per week exercise): 1.375x. Moderately Active (3 to 5 days): 1.55x. Very Active (6 to 7 days hard training): 1.725x. Extra Active (physical job plus hard daily training): 1.9x. The result is your Total Daily Energy Expenditure (TDEE), your maintenance calorie level.

Why does the Mifflin-St Jeor formula give different results for men and women?

The sex constant (+5 for men, -161 for women) captures the average difference in Basal Metabolic Rate due to body composition. Men have proportionally more skeletal muscle mass and less fat mass than women at equal body weight. Since muscle tissue burns more calories at rest than fat tissue, men have a higher BMR for the same weight and height. The 166 kcal gap reflects this population-average body composition difference.

Does BMR change as I lose weight?

Yes. As body weight decreases, BMR falls because there is less mass to maintain. A meaningful weight loss of 5 to 10 kg typically reduces BMR by 100 to 200 kcal per day. This is why calorie targets should be recalculated every 4 to 6 weeks during a weight-loss program. Losing lean muscle during a deficit accelerates the BMR drop, which is why adequate protein intake and resistance training are important during fat loss.

Is Mifflin-St Jeor accurate for obese individuals?

Mifflin-St Jeor performs reasonably well for overweight individuals but may slightly overestimate BMR in severely obese individuals because the formula does not distinguish between fat mass and lean mass. For people with obesity (BMI over 35), the Katch-McArdle formula (which uses lean body mass) can provide a more accurate estimate if body fat percentage is known. For most users, Mifflin-St Jeor remains the best general-purpose formula.

Can I use Mifflin-St Jeor BMR to calculate how many calories I need to lose weight?

Yes. Calculate your TDEE using BMR x activity factor. Then subtract 300 to 500 kcal from TDEE to create a moderate deficit. A 500 kcal/day deficit produces roughly 0.5 kg of fat loss per week. Never eat below 1,200 kcal (women) or 1,500 kcal (men) without medical supervision. Adjust your intake if actual weight change does not match the expected rate after 2 to 3 weeks of tracking.

How does age affect BMR according to the Mifflin-St Jeor formula?

In the Mifflin-St Jeor equation, each year of age reduces BMR by 5 kcal (because of the -5 x age term). For a 70-year-old versus a 30-year-old at the same weight and height, the older person's BMR is 200 kcal per day lower. In practice, this reflects the gradual loss of lean muscle mass (sarcopenia) that occurs with aging. Regular resistance training significantly slows this decline.

What is the difference between BMR and RMR?

Basal Metabolic Rate (BMR) is technically measured under highly controlled conditions: complete rest, thermoneutral environment, post-absorptive state (no food for 12 hours). Resting Metabolic Rate (RMR) is measured under less strict conditions and is typically 10 to 20% higher than true BMR. In practice, the terms are used interchangeably in nutrition software and online calculators. The Mifflin-St Jeor formula estimates BMR but is often used as an RMR proxy.

📌 Quick Tips

💡The Mifflin-St Jeor equation is the most accurate BMR formula for the general population, predicting within 10% of measured metabolic rate for about 82% of adults, versus 72% for Harris-Benedict.

💡BMR accounts for roughly 60 to 75 percent of your total daily energy expenditure. Even on complete rest days, you burn the majority of your calories keeping your organs running.

💡Activity level is the single largest variable in your TDEE estimate. Most people who exercise 3 to 4 days per week fall into the Lightly Active category (1.375x), not Moderately Active (1.55x). Overestimating activity level is the most common TDEE mistake.

💡BMR declines gradually with age (roughly 1 to 2 percent per decade after 30) because lean muscle mass decreases. Strength training is the most effective way to slow this decline and keep metabolic rate higher as you age.

💡If your actual weight change does not match what the calorie target predicts after 2 to 3 weeks, adjust by 100 to 200 kcal in the appropriate direction. All formulas are estimates within a range, not exact measurements.