BMR Calculator Guide

What This Calculator Does

BMR (Basal Metabolic Rate) describes energy used to support basic physiological functions under specific resting conditions. An online calculator cannot replace a controlled metabolic measurement, so this page compares three common equations, averages the available resting-energy estimates, and applies activity factors to derive TDEE (Total Daily Energy Expenditure).

The page shows Revised Harris–Benedict, Mifflin–St Jeor, optional Katch–McArdle, the available-formula average, and TDEE across five activity levels from sedentary to very active. It does not calculate a weight-loss or weight-gain target, read food logs, or model illness, medication, training cycles, or laboratory measurements.

When to Use It

• You want a first estimate of resting energy.
• You want to compare how common equations differ for the same inputs.
• You want to turn a resting estimate into TDEE under several activity assumptions.
• You need a starting number for a maintenance, fat-loss, or weight-gain plan that you can later calibrate.

The controls start at age 18, so this is intended as an adult planning reference. Do not rely on it alone for children or teens, pregnancy or breastfeeding, chronic illness, medication that affects appetite or metabolism, eating disorders, or unexplained weight change.

Inputs Explained

Sex

Revised Harris–Benedict and Mifflin–St Jeor use separate male and female coefficient sets, so the selection changes those outputs. It is a formula parameter, not a complete description of sex-related physiology, gender identity, or health status.

Age

Age is entered in years and affects both primary equations. The control accepts 18–100 years; that is a page range, not a claim that the equations fit every age or physiological stage equally well.

Height and Weight

Enter height in centimeters and weight in kilograms. The controls accept 100–250 cm and 30–200 kg. Use recent positive measurements; the page does not infer units, clothing weight, or measurement error.

Body Fat (Optional)

Body fat accepts 0–60%. When it is blank, the page calculates only Revised Harris–Benedict and Mifflin–St Jeor. When a positive value is supplied, it adds a Katch–McArdle reference based on lean mass. Error in a home-device or visual estimate carries directly into that result.

How the Calculation Works

Let weight be W kg, height be H cm, age be A years, and body fat be F percent.

Revised Harris–Benedict

• Male: BMR = 66.47 + 13.75 × W + 5.003 × H − 6.755 × A
• Female: BMR = 655.1 + 9.563 × W + 1.85 × H − 4.676 × A

Mifflin–St Jeor

• Male: BMR = 10 × W + 6.25 × H − 5 × A + 5
• Female: BMR = 10 × W + 6.25 × H − 5 × A − 161

Katch–McArdle (when body fat is entered)

• Lean body mass: LBM = W × (1 − F ÷ 100)
• Reference estimate: 370 + 21.6 × LBM

Katch–McArdle is a lean-mass-based resting-energy estimate and is conceptually closer to RDEE than a strict basal measurement. The page includes it as an extra formula reference, not as a promise that it is more accurate for every user. The page averages two outputs when body fat is blank and three when a valid positive body-fat value is supplied.

TDEE is calculated from the unrounded formula average using five factors: sedentary 1.2, light 1.375, moderate 1.55, active 1.725, and very active 1.9. Displayed BMR and TDEE values are rounded to whole kcal/day.

Example

Suppose the inputs are male, age 30, height 170 cm, weight 70 kg, with body fat left blank:

• Revised Harris–Benedict: 66.47 + 13.75 × 70 + 5.003 × 170 − 6.755 × 30 = 1676.83 kcal/day
• Mifflin–St Jeor: 10 × 70 + 6.25 × 170 − 5 × 30 + 5 = 1617.5 kcal/day
• Available-formula average: (1676.83 + 1617.5) ÷ 2 = 1647.165, displayed as about 1647 kcal/day
• Sedentary TDEE: 1647.165 × 1.2 ≈ 1977 kcal/day
• Moderate TDEE: 1647.165 × 1.55 ≈ 2553 kcal/day
• Very active TDEE: 1647.165 × 1.9 ≈ 3130 kcal/day

This demonstrates the page's arithmetic. It is not a guarantee of personal metabolism, and TDEE is not a fixed amount you must eat every day.

How to Understand the Result

Formula-Specific Results

Different equations produce different outputs because their coefficients and assumptions differ. Read them as an estimate range, not proof that one day’s metabolism has changed.

Available-Formula Estimate

This is a simple arithmetic mean of the currently available outputs. It is a convenient planning baseline, not a clinical standard or a measured “true BMR.”

TDEE

TDEE multiplies the average estimate by an activity factor and is closer to full-day energy use than BMR. The activity tier is still a simplified proxy: work, steps, training, sleep, illness, and tracking error can move real expenditure away from it.

Common Mistakes

• Treating BMR as total daily calorie needs.
• Treating TDEE as a fixed measurement every day.
• Assuming the average of three equations must be more accurate than one equation.
• Trusting Katch–McArdle when the body-fat input is unreliable.
• Choosing very active because of one occasional hard workout.
• Judging an equation from one day of scale change instead of several weeks of trend.
• Applying an adult estimate directly during adolescence, pregnancy, breastfeeding, illness, or an eating disorder.

FAQ

Which equation is the most accurate?

No equation is best for every person. A calculator converts population data into a starting estimate; this page’s average supports comparison and planning, not a measured or guaranteed value. Seek appropriate professional assessment when precision matters.

Are BMR, RMR, and TDEE the same?

No. Strict BMR measurements use more constrained resting conditions, while RMR/REE is often used for a broader resting-energy concept. TDEE adds daily activity. This page presents formula-based resting estimates and derives TDEE with activity factors.

Do I have to enter body fat?

No. Without it, the page still shows the two primary equations and their average. Katch–McArdle is most interpretable when body-fat data is reasonably trustworthy.

Can I use the result directly to set fat-loss calories?

Only as a first trial point, not as a prescription. This page does not model a deficit, minimum intake, or dynamic weight change; adjust from several weeks of trend, training, hunger, and professional guidance.

Notes

• These are equation-based estimates, not indirect calorimetry or another laboratory metabolic test.
• Averaging available equations is a page presentation choice, not a universal medical standard.
• Activity factors are rough proxies; TDEE cannot guarantee maintenance or a fixed rate of weight change.
• Body-fat error affects the lean-mass method, and the page does not model illness, medication, pregnancy, breastfeeding, training cycles, sleep, food logs, or metabolic adaptation.
• Use the result as an adult planning baseline. Children/teens, pregnancy/breastfeeding, chronic illness, eating disorders, or unexplained weight change call for a clinician or registered dietitian.