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● Metabolism & diet

Your Basal Metabolic Rate from two formulas.

BMR is the number of calories your body burns at complete rest. This calculator computes it using both Harris-Benedict (1984) and Mifflin-St Jeor (1990) side by side, so you can see how the estimates compare.

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BMR — Basal Metabolic Rate
Harris-Benedict vs. Mifflin-St Jeor — calories burned at rest per day
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Your data

yrs
in
lb
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Your BMR

— kcal/day
Mifflin-St Jeor
Formula comparison
Mifflin
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H-Benedict
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Mifflin-St Jeor BMRrecommended for most people—
Harris-Benedict BMRrevised 1984 formula—
DifferenceHarris-Benedict minus Mifflin—
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How it's calculated

Two equations, one goal: your resting calorie burn

The BMR (Basal Metabolic Rate) calculator computes the calories your body needs at complete rest using two validated equations. For a 30-year-old male, 175 cm, 70 kg: Mifflin BMR ≈ 1,695 kcal/day; Harris-Benedict BMR ≈ 1,725 kcal/day. Mifflin-St Jeor (1990) is generally considered more accurate for modern populations.

BMR represents the energy consumed by vital functions — heartbeat, breathing, kidney filtration, cell maintenance — with no physical activity. Both formulas use sex, age, height and weight. They differ in their constants: Mifflin-St Jeor was derived in 1990 on a population closer to today's average; Harris-Benedict was revised in 1984 from a 1919 study.

Mifflin-St Jeor
Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5
Women: BMR = (10 × kg) + (6.25 × cm) − (5 × age) − 161

Harris-Benedict (1984)
Men: BMR = (13.397 × kg) + (4.799 × cm) − (5.677 × age) + 88.362
Women: BMR = (9.247 × kg) + (3.098 × cm) − (4.330 × age) + 447.593
  1. 1
    Convert inputs to metric (kg and cm)
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  2. 2
    Apply Mifflin-St Jeor formula
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  3. 3
    Apply Harris-Benedict (revised 1984) formula
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  4. 4
    Compare both estimates
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Understand the terms

BMR (Basal Metabolic Rate)
Calories burned per day at complete rest — no digestion, no movement. Represents the minimum energy the body needs to sustain vital functions.
TDEE (Total Daily Energy Expenditure)
BMR multiplied by an activity factor (1.2–1.9). TDEE is the calorie target you eat at to maintain your current weight.
Mifflin-St Jeor equation
Published in 1990 by Mifflin et al. Generally the most accurate formula for predicting resting metabolic rate in modern adults. Preferred by most dietitians.
Harris-Benedict equation
Originally from 1919, revised by Roza & Shizgal in 1984. Tends to overestimate BMR slightly in overweight populations.
Lean mass
Body mass minus fat — muscle, bone, organs, water. Higher lean mass means a higher BMR, since muscle burns more calories than fat at rest.
See the full glossary →
Disclaimer: estimation tool for informational and planning purposes, using Mifflin-St Jeor (1990) and Harris-Benedict (revised 1984) formulas. Actual BMR may vary by ±10–15% depending on body composition, genetics and hormonal status. Does not replace assessment by a registered dietitian or physician.
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Frequently asked questions — BMR

What is BMR (Basal Metabolic Rate)?
BMR is the number of calories your body burns at complete rest over 24 hours to maintain vital functions — breathing, circulation, cell repair, and temperature regulation. It accounts for roughly 60–70% of your total daily energy expenditure and is the foundation for any calorie-based nutrition plan.
Which BMR formula is more accurate — Harris-Benedict or Mifflin-St Jeor?
The Mifflin-St Jeor equation (1990) is generally considered more accurate for modern populations. Studies show it predicts resting metabolic rate within about 10% for most adults. Harris-Benedict (revised 1984) tends to overestimate BMR slightly, especially in overweight individuals. Most registered dietitians prefer Mifflin-St Jeor as the starting point.
How do I use my BMR to set a calorie goal?
Multiply your BMR by an activity factor to get your TDEE (Total Daily Energy Expenditure): 1.2 for sedentary (desk job, little exercise), 1.375 for light activity (1–3 days/week), 1.55 for moderate (3–5 days/week), 1.725 for very active (6–7 days/week), 1.9 for extremely active (physical job + training). To lose weight, eat 500–750 kcal below your TDEE. To gain muscle, eat 200–500 kcal above it.
Does BMR change with age?
Yes. BMR typically decreases with age, primarily due to loss of lean muscle mass (sarcopenia). After age 30, BMR can decline by about 1–2% per decade. Strength training and adequate protein intake help preserve muscle mass and slow this decline. The formulas already incorporate age as a variable to account for this.
What factors affect BMR?
The main factors are: body size (height and weight), body composition (muscle burns more calories than fat at rest), age (declines with age), sex (men generally have higher BMR due to more muscle mass), genetics, thyroid hormones (hyperthyroidism raises BMR; hypothyroidism lowers it), and ambient temperature (cold environments increase BMR slightly). The standard formulas capture sex, age, height and weight — they do not account for body composition differences.

📚 Learn more — official sources

🔬 Study Mifflin et al. (1990) — A new predictive equation for resting energy expenditure Original publication of the Mifflin-St Jeor equation in The American Journal of Clinical Nutrition, validated against indirect calorimetry. See on PubMed → 🔬 Study Roza & Shizgal (1984) — The Harris-Benedict equation reevaluated Revised Harris-Benedict constants used today, correcting the original 1919 study using more precise calorimetry methods. See on PubMed → 🏛️ Organization NIH — Weight management and energy balance National Institute of Diabetes and Digestive and Kidney Diseases guide on energy balance, calorie needs, and weight management strategies. See official source → 🏛️ Organization WHO — Healthy diet and calorie guidelines World Health Organization recommendations on daily energy intake, macronutrient balance, and diet quality for healthy adults. See official source →

About the BMR Calculator

The Basal Metabolic Rate is the cornerstone of any evidence-based nutrition plan. Knowing how many calories your body burns at rest allows you to set realistic targets for weight loss, maintenance, or muscle gain — by applying an activity multiplier to get your TDEE.

This calculator presents both Mifflin-St Jeor (1990) and Harris-Benedict (revised 1984) side by side. Mifflin is the preferred equation in most clinical settings today; Harris-Benedict remains widely used and provides a useful cross-check. The visual bar makes the difference between formulas immediately clear.

For a more complete metabolic picture, consider pairing your BMR with a body composition measurement (such as RFM or the Navy body fat method) to estimate how much of your weight is muscle versus fat — since lean mass is the primary driver of resting calorie burn.

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