Whether you are checking a nutrition assignment, building a spreadsheet, or comparing calorie calculators, three questions come up repeatedly: How is the Mifflin–St Jeor equation calculated step by step? Which activity multiplier (1.2 to 1.9) should I choose without double-counting exercise? And why doesn’t a fixed daily calorie deficit produce linear weight loss?

This guide breaks down the Mifflin–St Jeor equations (Mifflin et al., 1990), traces a complete worked example (age 30, 175 cm, 70 kg), compares the 5-tier activity multipliers against Japan’s Physical Activity Levels (PAL), provides an age-by-sex BMR & TDEE lookup table (ages 20–60), and explains the dynamic energy-balance limits highlighted by the NIH/NIDDK Body Weight Planner.

Key Takeaways: Mifflin–St Jeor Equations & TDEE Formula
  • Male Equation (BMR/REE Estimate): 10 × Weight (kg) + 6.25 × Height (cm) − 5 × Age (years) + 5 (kcal/day)
  • Female Equation (BMR/REE Estimate): 10 × Weight (kg) + 6.25 × Height (cm) − 5 × Age (years) − 161 (kcal/day)
  • Total Daily Energy Expenditure (TDEE): BMR Estimate × Activity Factor (1.2 / 1.375 / 1.55 / 1.725 / 1.9)
Calculate Your BMR & TDEE Instantly in Your Browser

Select your equation, age, height (cm), weight (kg), and activity level to compute your resting energy estimate (BMR) and total daily calorie expenditure (TDEE). All calculations run locally on your device.

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1. Inside the Mifflin–St Jeor Equation: Variable Sensitivity & BMR vs. REE

Derived from indirect calorimetry measurements of 498 healthy adults in Mifflin et al. (1990), the Mifflin–St Jeor equation estimates adult resting energy expenditure in kilocalories per day ($\text{kcal/day}$):

Male Equation (kcal/day)=10W+6.25H−5A+5Female Equation (kcal/day)=10W+6.25H−5A−161\begin{aligned} \text{Male Equation (kcal/day)} &= 10W + 6.25H - 5A + 5 \\ \text{Female Equation (kcal/day)} &= 10W + 6.25H - 5A - 161 \end{aligned}

Here $W$ is body weight in kilograms ($\text{kg}$), $H$ is height in centimeters ($\text{cm}$), and $A$ is age in years. Unlike the BMI formula—where height must be converted to meters and squared (see the BMI Calculation Guide)—the Mifflin–St Jeor equation takes height directly in centimeters (for unit conversions, see the Unit Conversion Guide).

Term / Variable Male Equation Female Equation Marginal Sensitivity (Change per Unit) Calculation & Interpretation Note
Weight Term ($10W$) $+10 \times \text{Weight (kg)}$ $+10 \times \text{Weight (kg)}$ +10 kcal/day per +1 kg of body weight Scales linearly with total mass without separating fat-free mass from fat mass
Height Term ($6.25H$) $+6.25 \times \text{Height (cm)}$ $+6.25 \times \text{Height (cm)}$ +6.25 kcal/day per +1 cm of height Enter height in centimeters (cm), not meters
Age Term ($-5A$) $-5 \times \text{Age (years)}$ $-5 \times \text{Age (years)}$ −5 kcal/day per +1 year (−50 kcal per decade) Reflects average age-related decline in resting metabolic rate across adults
Sex Constant $+5$ $-161$ 166 kcal/day difference at identical $W, H, A$ Approximates average population differences in lean muscle proportion
Terminology Note: Basal Metabolic Rate (BMR) vs. Resting Energy Expenditure (REE)

Strictly speaking, Basal Metabolic Rate (BMR) is measured in the early morning after a 12–14 hour overnight fast under thermoneutral, supine rest. Mifflin et al. measured Resting Energy Expenditure (REE) under slightly less restrictive resting conditions. Like most nutrition calculators, our Calorie Calculator labels this output "BMR" by convention, but you should interpret and report it as a predictive resting-energy estimate, not a direct calorimetry measurement.

2. Worked Example in 3 Steps: Age 30, 175 cm, 70 kg (Factor 1.375)

Let’s trace the calculation for a 30-year-old who is 175 cm tall, weighs 70 kg, and selects the male equation with Light Activity (factor 1.375):

Step 1
Compute the weight, height, and age terms

Multiply each input by its coefficient:
• Weight term: 10 × 70 kg = 700
• Height term: 6.25 × 175 cm = 1,093.75
• Age term: 5 × 30 years = 150

Step 2
Apply the sex constant (+5 for the male equation) to get unrounded BMR

700 + 1,093.75 − 150 + 5 = 1,648.75 kcal/day
*(Using the female equation with constant −161 for the same inputs gives 1,648.75 − 166 = 1,482.75 kcal/day.)* Our Calorie Calculator rounds the displayed BMR to the nearest integer (1,649 kcal/day).

Step 3
Multiply the unrounded BMR by the activity factor (1.375) to get TDEE

1,648.75 kcal/day × 1.375 = 2,267.03125 kcal/day
Rounding to the nearest whole number yields 2,267 kcal/day. Always keep full precision during intermediate steps and round only at the end (see the Significant Figures & Rounding Guide).

Workflow diagram of the Mifflin–St Jeor BMR equation and 5-tier activity multipliers producing Total Daily Energy Expenditure (TDEE) for age 30, 175 cm, 70 kg
Figure 1: Step-by-step Mifflin–St Jeor BMR calculation (1,648.75 kcal/day for age 30, 175 cm, 70 kg) and TDEE scaling across the five activity multipliers.

3. Choosing an Activity Factor (1.2 to 1.9) & Avoiding Double-Counting

For the exact same BMR estimate ($1,648.75\text{ kcal/day}$), switching from 1.2 to 1.9 shifts estimated TDEE from 1,978.5 kcal/day to 3,132.6 kcal/day—a spread of more than 1,150 kcal/day.

Calculator Activity Level Multiplier Typical Weekly Activity Pattern Worked Example TDEE (Unrounded → Displayed) Common Selection Pitfall
Sedentary (little or no exercise) 1.2 Desk job, commuting, everyday household tasks without structured workouts 1,978.50 kcal → 1,979 kcal/day Best baseline if you sit 8+ hours/day and do not exercise regularly
Lightly active (1–3 days/week) 1.375 Light jogging, strength training 1–3 days/week, or high daily step count 2,267.03 kcal → 2,267 kcal/day One short weekend workout with a sedentary week is often closer to 1.2–1.3
Moderately active (3–5 days/week) 1.55 Structured aerobic or resistance training 3–5 days/week 2,555.56 kcal → 2,556 kcal/day Do not add smartwatch workout calories on top of this multiplier
Very active (6–7 days/week) 1.725 Hard training or vigorous sports nearly every day 2,844.09 kcal → 2,844 kcal/day Frequently overestimated by recreational gym-goers
Extra active (very hard exercise/job) 1.9 Manual labor (construction, agriculture) or twice-daily athletic training 3,132.63 kcal → 3,133 kcal/day Rarely applicable outside competitive endurance sports or heavy labor
Important: Tool Multipliers vs. Japan's Dietary Reference Intakes (PAL)

Do not equate the five multipliers above (`1.2` to `1.9`) one-to-one with the Physical Activity Levels (PAL) in Japan's Dietary Reference Intakes (MHLW). The Japanese public standard uses three PAL tiers (Level I Low = 1.50, Level II Normal = 1.75, Level III High = 2.00 for ages 18–64) paired with Japanese reference basal metabolic rate tables rather than the Mifflin–St Jeor equation. Always follow the specific protocol required by your course or study.

4. Age & Sex Reference Matrix (Ages 20–60)

Because the age term is $-5A$, predicted BMR decreases by 50 kcal/day per decade when height and weight remain constant. The table below shows reference outputs for two representative adult profiles: Male equation at 170 cm, 65 kg and Female equation at 158 cm, 52 kg.

Equation & Stature Age BMR Estimate (kcal/day) TDEE: Sedentary (×1.2) TDEE: Light (×1.375) TDEE: Moderate (×1.55)
Male Equation
170 cm / 65 kg		 20 yrs 1,617.5 (displays 1,618) 1,941 kcal/day 2,224 kcal/day 2,507 kcal/day
Male Equation
170 cm / 65 kg		 30 yrs 1,567.5 (displays 1,568) 1,881 kcal/day 2,155 kcal/day 2,430 kcal/day
Male Equation
170 cm / 65 kg		 40 yrs 1,517.5 (displays 1,518) 1,821 kcal/day 2,087 kcal/day 2,352 kcal/day
Male Equation
170 cm / 65 kg		 50 yrs 1,467.5 (displays 1,468) 1,761 kcal/day 2,018 kcal/day 2,275 kcal/day
Male Equation
170 cm / 65 kg		 60 yrs 1,417.5 (displays 1,418) 1,701 kcal/day 1,949 kcal/day 2,197 kcal/day
Female Equation
158 cm / 52 kg		 20 yrs 1,246.5 (displays 1,247) 1,496 kcal/day 1,714 kcal/day 1,932 kcal/day
Female Equation
158 cm / 52 kg		 30 yrs 1,196.5 (displays 1,197) 1,436 kcal/day 1,645 kcal/day 1,855 kcal/day
Female Equation
158 cm / 52 kg		 40 yrs 1,146.5 (displays 1,147) 1,376 kcal/day 1,576 kcal/day 1,777 kcal/day
Female Equation
158 cm / 52 kg		 50 yrs 1,096.5 (displays 1,097) 1,316 kcal/day 1,508 kcal/day 1,700 kcal/day
Female Equation
158 cm / 52 kg		 60 yrs 1,046.5 (displays 1,047) 1,256 kcal/day 1,439 kcal/day 1,622 kcal/day

5. Why a Fixed Calorie Deficit Does Not Guarantee Linear Weight Loss

As explained in the NIH/NIDDK Body Weight Planner, multiplying a fixed daily calorie deficit by the number of days does not accurately predict an individual’s weight trajectory:

  1. Dynamic metabolic adaptation: Losing weight lowers both the $10W$ mass term and adaptive thermogenesis (including non-exercise activity thermogenesis, or NEAT), progressively narrowing the net energy deficit over time.
  2. Glycogen and extracellular water shifts: Early weight changes over days or weeks largely reflect glycogen stores and bound water rather than pure adipose tissue change.
  3. Body composition differences: Because the Mifflin–St Jeor equation uses total weight rather than fat-free mass, two individuals at 175 cm and 70 kg with very different muscle-to-fat ratios receive the same arithmetic BMR estimate.
  4. Population exclusions: This adult equation should not be used alone to prescribe energy intake for children, adolescents under 18, pregnant or lactating individuals, or patients managing metabolic, endocrine, or renal conditions.

6. How to Reproduce the Example in the Calorie Calculator

To verify the worked example in the Calorie Calculator:

  1. Select Sex Equation: Choose Male (applies the +5 constant).
  2. Enter Age, Height, and Weight: Type Age 30 (integer 18–120), Height 175 (100–250 cm), and Weight 70 (20–300 kg).
  3. Select Activity Level: Choose Lightly active (light exercise 1-3 days/week) (1.375) and click Calculate.
  4. Verify the outputs:
    • Basal Metabolic Rate (BMR): 1,649 kcal/day (1,648.75 rounded to integer)
    • Total Daily Energy Expenditure (TDEE): 2,267 kcal/day (2,267.03125 rounded to integer)
Combine Your Energy Estimate with a BMI & Reference Weight Check

Test different activity multipliers in the Calorie Calculator, then check your BMI and BMI-22 reference weight in the BMI Calculator.

Open Calorie Calculator → Open BMI Calculator →

7. Related Tools & Further Reading

Verification & Update Log

On November 9, 2026, we verified the equations and interpretation notes against Mifflin et al. (1990), the NIDDK Body Weight Planner, and Japan’s Dietary Reference Intakes, adding the variable sensitivity table, PAL comparison, and ages 20–60 reference matrix.

FAQ

What are the BMR and TDEE for age 30, 175 cm, and 70 kg using the male equation and 1.375 activity factor?

Substituting into the male Mifflin–St Jeor equation gives BMR = 10(70) + 6.25(175) − 5(30) + 5 = 700 + 1,093.75 − 150 + 5 = 1,648.75 kcal/day (rounded to 1,649 kcal/day in the calculator). Multiplying the unrounded BMR by 1.375 (light activity) yields TDEE = 1,648.75 × 1.375 = 2,267.03125 kcal/day (displayed as 2,267 kcal/day).

Should I add smartwatch exercise calories on top of my TDEE?

Generally no. Activity multipliers (such as 1.375 for light exercise 1–3 days/week or 1.55 for moderate exercise 3–5 days/week) already average weekly exercise energy expenditure across all seven days. Adding exercise calories separately on top of an activity-adjusted TDEE double-counts physical activity.

How do the tool's 5 activity factors differ from Japan's Physical Activity Levels (PAL)?

Our calculator uses the five standard international multipliers (1.2, 1.375, 1.55, 1.725, 1.9) paired with the Mifflin–St Jeor equation. Japan's Dietary Reference Intakes instead multiply age-specific Japanese reference basal metabolic standards by three Physical Activity Levels (PAL I = 1.50, PAL II = 1.75, PAL III = 2.00 for ages 18–64). When completing academic coursework or clinical protocols, always use the specific definitions required by your reference source.

Why doesn't a fixed 500 kcal/day deficit produce linear weight loss forever?

Static rules (such as equating 3,500 kcal to 1 lb or ~7,200 kcal to 1 kg of fat) ignore metabolic adaptation and changing body mass. As weight decreases, resting energy expenditure and non-exercise activity thermogenesis (NEAT) decline, shrinking the actual energy deficit. Short-term scale weight also fluctuates with glycogen and extracellular water, as documented by the NIH/NIDDK Body Weight Planner.