What are the exact coefficients used in the Mifflin-St Jeor equation?

The engine computes (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years), then adds 5 for males or subtracts 161 for females. These coefficients match the original 1990 Mifflin-St Jeor paper and are applied exactly as written in the calculator's source code.

How accurate is the Mifflin-St Jeor equation in practice?

Studies comparing the equation against measured resting energy expenditure find it accurate to within roughly 10 percent for most healthy adults of average body composition, but individual variation can exceed that range — particularly for people with high muscle mass, older adults, or those with metabolic conditions. It is a screening estimate, not a clinical measurement.

Should I use BMR or TDEE when planning calories?

TDEE is the more useful daily target because it accounts for your activity level, whereas BMR assumes you are completely at rest. Use BMR to understand your resting baseline; use TDEE as the starting point for your daily intake estimate, then adjust based on your own weight trend over several weeks.

Is this article or the calculator medical advice?

No. Both are screening tools that produce population-level estimates from a formula. They are not medical, nutritional, or dietary advice. For guidance tailored to your health, goals, and circumstances, consult a doctor or registered dietitian.

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How does the Mifflin-St Jeor equation estimate your daily calories?

By CalorieLab · Published June 10, 2026 · Updated June 10, 2026

The Mifflin-St Jeor equation calculates resting calorie use as (10 × weight in kg) + (6.25 × height in cm) − (5 × age) + 5 for males or − 161 for females — for a 35-year-old male at 80 kg and 178 cm that produces a BMR of 1,743 kcal/day, which scales to 2,701 kcal at a moderate activity level.

The equation and its four inputs

The Mifflin-St Jeor equation was published in 1990 and remains the formula most commonly cited in dietetic practice for estimating resting calorie burn. It takes four measured values — weight in kilograms, height in centimetres, age in years, and biological sex — and combines them into a single number called the basal metabolic rate (BMR). No equipment is needed; the four measurements can be entered directly into the calculator.

The arithmetic is straightforward: multiply weight by 10, height by 6.25, and age by 5, then add those three terms together. For males the equation adds 5 to that sum; for females it subtracts 161. Those sex constants were fitted to measured resting energy expenditure data in the original study and reflect average differences in lean mass distribution. The engine in this calculator uses exactly these coefficients: base = (10 × weightKg) + (6.25 × heightCm) − (5 × age), then BMR = base + 5 for males or base − 161 for females.

A worked example computed by the engine

Consider a 35-year-old male weighing 80 kg and standing 178 cm tall. Applying the equation: (10 × 80) + (6.25 × 178) − (5 × 35) = 800 + 1,112.5 − 175 = 1,737.5, then add 5 for male sex, giving 1,742.5 kcal/day. The engine rounds to the nearest whole number, producing a BMR of 1,743 kcal/day. Running the same profile through the calculator with a moderate activity level (multiplier 1.55) yields a Total Daily Energy Expenditure of 2,701 kcal/day.

For comparison, a 28-year-old female weighing 65 kg and standing 165 cm produces a BMR of 1,380 kcal/day — computed as (10 × 65) + (6.25 × 165) − (5 × 28) − 161 = 650 + 1,031.25 − 140 − 161 = 1,380.25, rounded to 1,380. At the same moderate activity level, her TDEE is 2,139 kcal/day. These two profiles show how the sex constant and the four personal inputs combine to produce meaningfully different resting baselines for different people.

From BMR to TDEE — what the activity multiplier adds

BMR measures only resting burn — the energy needed to keep the heart beating, lungs breathing, and body temperature regulated while the body is completely still. Nobody's actual day looks like that, so the calculator scales BMR by an activity multiplier to reach Total Daily Energy Expenditure (TDEE): the estimated calories burned across a full day including movement, exercise, and the thermic effect of food. For the male example above, the five available multipliers produce TDEEs ranging from approximately 2,092 kcal/day at sedentary (1.2×) to 3,312 kcal/day at very active (1.9×) — a span of over 1,200 kcal driven by activity choice alone.

The five multiplier levels used in this calculator are: sedentary 1.2, lightly active 1.375, moderately active 1.55, very active 1.725, and extremely active 1.9. These are standard factors drawn from the Harris-Benedict revision lineage and are the same values the Mifflin-St Jeor paper assumed when converting BMR into population-level expenditure estimates. Choosing the wrong level — for example selecting "very active" when most days are a desk routine — is the single largest source of error in any multiplier-based TDEE estimate.

Goal adjustments — what the offset numbers mean

Once the calculator has a TDEE, it applies a flat daily offset for the chosen goal. Maintenance leaves TDEE unchanged: the 35-year-old male example at moderate activity stays at 2,701 kcal/day. The weight-loss offset subtracts 500 kcal/day — at light activity (multiplier 1.375, TDEE 2,396) the engine returns a target of 1,896 kcal/day. The muscle-gain offset adds 300 kcal/day — at active level (multiplier 1.725, TDEE 3,006) the engine returns 3,306 kcal/day. These are the exact values produced by the engine for that profile.

A 500 kcal daily deficit corresponds to roughly 3,500 kcal per week, which is the commonly cited energy equivalent of approximately 0.45 kilograms of body mass. The 300 kcal surplus for muscle gain is a conservative default intended to supply building energy while limiting concurrent fat accumulation. Both offsets are fixed population-level assumptions, not tailored prescriptions, and they do not adjust automatically for age-related metabolic slowdown, medication effects, or unusual body composition.

Why the equation is a population estimate, not a personal measurement

The Mifflin-St Jeor equation was derived from regression analysis of a group of adults, which means it minimises error across a population, not for any single individual. Someone with an unusually high proportion of lean muscle mass will burn more than the equation predicts because muscle is metabolically more active than fat, yet both individuals with very different body compositions could have the same weight, height, age, and sex. Older adults often see a larger gap between predicted and measured BMR because lean mass declines with age in ways the equation does not directly capture.

Medical conditions that affect metabolic rate — including thyroid disorders, adrenal conditions, and certain medications — can shift actual energy needs well outside the equation's output, sometimes by hundreds of kilocalories per day. Because this calculator runs a formula rather than a metabolic measurement, it cannot detect any of these factors. The result is a general screening estimate useful as a planning reference or a starting point for a conversation with a clinician or registered dietitian, not a substitute for that conversation. Always consult a qualified healthcare professional before making changes to your diet, especially if you have a health condition, are pregnant, or are taking medication.

Questions

What are the exact coefficients used in the Mifflin-St Jeor equation?: The engine computes (10 × weight in kg) + (6.25 × height in cm) − (5 × age in years), then adds 5 for males or subtracts 161 for females. These coefficients match the original 1990 Mifflin-St Jeor paper and are applied exactly as written in the calculator's source code.
How accurate is the Mifflin-St Jeor equation in practice?: Studies comparing the equation against measured resting energy expenditure find it accurate to within roughly 10 percent for most healthy adults of average body composition, but individual variation can exceed that range — particularly for people with high muscle mass, older adults, or those with metabolic conditions. It is a screening estimate, not a clinical measurement.
Should I use BMR or TDEE when planning calories?: TDEE is the more useful daily target because it accounts for your activity level, whereas BMR assumes you are completely at rest. Use BMR to understand your resting baseline; use TDEE as the starting point for your daily intake estimate, then adjust based on your own weight trend over several weeks.
Is this article or the calculator medical advice?: No. Both are screening tools that produce population-level estimates from a formula. They are not medical, nutritional, or dietary advice. For guidance tailored to your health, goals, and circumstances, consult a doctor or registered dietitian.