What Is the Mifflin-St Jeor Equation?

Published in 1990 by Mifflin, St Jeor, and colleagues, this equation estimates resting energy expenditure (REE/BMR) from weight, height, age, and sex. It was derived from indirect calorimetry in 498 healthy adults and is widely used as a default BMR formula in nutrition software and clinical references. Frankenfield et al. (2005) found it within ~10% of measured RMR for roughly 82% of non-obese adults and ~70% of obese adults — better than many older equations, though still a population estimate, not your measured metabolic rate.

The Mifflin-St Jeor Formula

Mifflin-St Jeor (1990)

Male:
BMR = (10 × kg) + (6.25 × cm)
    − (5 × age) + 5

Female:
BMR = (10 × kg) + (6.25 × cm)
    − (5 × age) − 161
kg
Body weight in kilograms
cm
Height in centimeters
age
Age in years

Every variable is required: weight and height scale resting metabolism, age captures gradual decline, and the sex constant (+5 men / −161 women) reflects average body-composition differences at the population level.

How the Formula Works

Term

10 × weight (kg)

Effect on BMR

Larger bodies need more energy

Note

Largest positive driver for most adults

Term

6.25 × height (cm)

Effect on BMR

Taller frames add REE

Note

Reflects organ and surface-area scaling

Term

−5 × age

Effect on BMR

Gradual decline with age

Note

Partly reflects lean-mass changes

Term

Sex constant

Effect on BMR

+5 (men) / −161 (women)

Note

Population average, not individual destiny

Your calculator results show these contributions as bars — useful for understanding how weight, height, age, and sex combine in your estimate.

Worked Examples

Adult male: 35 years, 180 cm, 80 kg

Standard Mifflin-St Jeor.

  1. BMR = (10 × 80) + (6.25 × 180) − (5 × 35) + 5
  2. BMR = 800 + 1,125 − 175 + 5 = 1,755 kcal/day

Result: Estimated BMR ≈ 1,755 kcal/day

Adult female: 30 years, 165 cm, 62 kg

Standard Mifflin-St Jeor.

  1. BMR = (10 × 62) + (6.25 × 165) − (5 × 30) − 161
  2. BMR = 620 + 1,031 − 150 − 161 = 1,340 kcal/day

Result: Estimated BMR ≈ 1,340 kcal/day

BMR vs RMR vs TDEE

Metric

BMR

What it measures

Resting energy under strict conditions

Best use

Baseline; Mifflin estimates this

Metric

RMR

What it measures

Resting energy, less strict protocol

Best use

Often 3–10% higher than BMR in labs

Metric

TDEE

What it measures

Total daily energy (BMR × activity factor)

Best use

Daily calorie planning; multipliers embed typical activity + TEF

Activity Multipliers

TDEE ≈ BMR × activity factor. Standard multipliers (1.2–1.9) are simplified planning values that approximate activity, NEAT, and typical thermic effect of food — not a separate TEF add-on. Pick the level that matches an average week — not your most active day. When unsure, use the Activity Level Quiz for a precise multiplier.

Level

Sedentary

Factor

1.2

Real-life example

Desk job, little formal exercise

Level

Lightly Active

Factor

1.375

Real-life example

Light exercise 1–3 days/week

Level

Moderately Active

Factor

1.55

Real-life example

Moderate exercise 3–5 days/week

Level

Very Active

Factor

1.725

Real-life example

Hard training 6–7 days/week

Level

Extra Active

Factor

1.9

Real-life example

Physical job + daily hard training

Mifflin-St Jeor vs Harris-Benedict

Aspect

Year / population

Mifflin-St Jeor

1990; 498 healthy adults

Harris-Benedict (1984)

1984 revision of 1919 equation

Aspect

Typical accuracy

Mifflin-St Jeor

Within ~10% for many adults (Frankenfield 2005)

Harris-Benedict (1984)

Often slightly higher; useful cross-check

Aspect

Best use

Mifflin-St Jeor

Default when BF% unknown

Harris-Benedict (1984)

Comparison when formulas diverge >100 kcal

Aspect

Limitation

Mifflin-St Jeor

Does not use body composition

Harris-Benedict (1984)

Same — total weight only

Mifflin-St Jeor vs Katch-McArdle

Katch-McArdle uses lean body mass (from body fat %) and can be more appropriate when composition is far from average — but only with a reliable body-fat measurement.

Katch-McArdle

Lean mass (kg) = weight (kg)
    × (1 − body fat % / 100)

BMR = 370 + (21.6 × lean mass kg)
kg
Body weight in kilograms
BF%
Body fat percentage (required)

Shown in results only when you enter body fat %.

Profile

General population, BF% unknown

Often better starting point

Mifflin-St Jeor

Profile

Lean / muscular athlete with known BF%

Often better starting point

Consider Katch-McArdle

Profile

Higher body fat, BF% from DEXA or reliable method

Often better starting point

Katch may reduce overestimate from fat mass

Profile

Guessed body fat %

Often better starting point

Stick with Mifflin — bad BF% hurts Katch

Accuracy & Error Sources

TDEE estimate error comes from two stacked layers — and the second is usually bigger in practice.

Layer 1: BMR formula error

Mifflin-St Jeor predicts resting metabolic rate within ~10% for roughly 82% of non-obese adults and ~70% of obese adults (Frankenfield et al., 2005). That is ±150–200 kcal for many people.

Layer 2: Activity multiplier error

Picking one activity bucket too high adds ~200–400 kcal/day. Most people remember gym time but underestimate desk hours. Take our Activity Level Quiz if unsure.

  • Individual thyroid, medication, and illness effects are not modeled.
  • Activity self-report is often a larger error source than the BMR equation itself.
  • Recalculate after ~5–10 kg (10–15 lb) weight change or every 4–6 weeks.

Factors Affecting BMR

  • Age — gradual decline; captured by the −5 × age term.
  • Body size & composition — more lean mass generally means higher REE.
  • Sex — population constant; individual variation still large.
  • Genetics & hormones — not in the equation; part of individual spread.
  • Sleep, stress, illness — can shift expenditure temporarily.
  • Diet history — prolonged very-low intake may affect measured REE over time.

Supporting Metabolic Health

No food or habit permanently "fixes" a slow metabolism in the way marketing often claims. Evidence-supported habits that help maintain lean mass and daily expenditure include:

  • Resistance training to preserve muscle during fat loss.
  • Adequate protein (often ~1.6–2.2 g/kg/day for many active adults — see macro tool).
  • Regular daily movement (NEAT) beyond structured gym sessions.
  • Consistent sleep and recovery.
  • Hydration and balanced energy intake over crash dieting.

Common Mistakes

Myth

BMR is my daily calorie target.

Evidence-based view

Most people need TDEE (BMR × activity) or higher. Eating at BMR alone is usually below maintenance.

Myth

Pick the highest activity level to avoid under-eating.

Evidence-based view

Overestimating activity adds 200–400+ kcal/day. Start conservative and adjust from weight trends.

Myth

The formula should be exact.

Evidence-based view

±10% individual variation is normal. Use 2–3 weeks of tracking to calibrate.

Myth

Mifflin works perfectly for every body.

Evidence-based view

Very high BMI, older adults, and atypical composition may need Katch-McArdle or trend-based verification.

How to Interpret Your Results

From BMR to actionable planning numbers.

Output

BMR

Meaning

Resting energy estimate

Next step

Multiply by activity for TDEE

Output

TDEE table

Meaning

Maintenance at each activity tier

Next step

Pick realistic level; use quiz if unsure

Output

Goal calories

Meaning

TDEE adjusted for deficit/surplus

Next step

Hand off to macro or deficit tools

Output

BMI band

Meaning

Weight-for-height context

Next step

Informational only — not a prescription

Safety & Limitations

Suggested next steps

TDEE Calculator

Full pipeline with macros

Maintenance Calculator

Focused maintenance estimate

Deficit Calculator

Compare deficit options

Macro Calculator

Protein, fat, carb grams

BMR Calculator

Multi-formula comparison tool

Methodology

All coefficients and sources

Research & References

Each citation below supports a specific claim on this page. We explain relevance so you can verify the science yourself.

  1. National Academies of Sciences, Engineering, and Medicine — Factors Affecting Energy Expenditure and Requirements. Dietary Reference Intakes for Energy — NCBI Bookshelf, 2023.Defines TDEE components (REE, TEF, PAEE) and explains why population equations cannot capture individual metabolic variation.
  2. Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO — A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr. 1990;51(2):241-247, 1990.DOI: 10.1093/ajcn/51.2.241Primary source for the Mifflin-St Jeor BMR equation used as the default in this calculator.
  3. Roza AM, Shizgal HM — The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. Am J Clin Nutr. 1984;40(1):168-182, 1984.DOI: 10.1093/ajcn/40.1.168Source for the revised Harris-Benedict coefficients offered as a comparison formula.
  4. McArdle WD, Katch FI, Katch VL — Exercise Physiology: Energy, Nutrition, and Human Performance. Lippincott Williams & Wilkins, 7th edition, 2010.Textbook reference for the lean-body-mass-based Katch-McArdle resting energy estimate.
  5. Frankenfield D, Roth-Yousey L, Compher C — Comparison of Predictive Equations for Resting Metabolic Rate in Healthy Nonobese and Obese Adults. J Am Diet Assoc. 2005;105(5):775-789, 2005.DOI: 10.1016/j.jada.2005.02.005Meta-analysis showing Mifflin-St Jeor within ~10% of measured RMR for ~82% of non-obese and ~70% of obese adults — supports honest accuracy framing.

Frequently Asked Questions

Common questions about the mifflin-st jeor calculator.