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BMR Calculator

Calculate your Basal Metabolic Rate using Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle formulas. Free, instant, and accurate.

✓ Tested formula & cited sources Checked against independent sources · Oct 18, 2026 Private: runs in your browser

Choose Imperial (lbs, ft/in) or Metric (kg, cm) for your measurements

Mifflin-St Jeor is recommended for most people. Katch-McArdle requires body fat %.

Used in BMR formulas — male and female equations use different constants

Age in years — BMR decreases ~2% per decade after age 20

Pounds (lbs) for Imperial · Kilograms (kg) for Metric

Imperial only

Imperial only — remaining inches (0–11)

Required for Katch-McArdle. Optional for comparison.

Results

BMR — Mifflin-St Jeor

1,737 kcal/day

Your body burns 1,737 kcal/day (72/hour) at complete rest — before any movement or digestion. The Mifflin-St Jeor equation (the +5 term is the male-specific constant) is an estimate (in validation studies the best-performing equation, Mifflin-St Jeor, was within 10% of measured resting metabolic rate for roughly 8 in 10 non-obese adults); your two formula estimates agree closely, which increases confidence in the number. Remember BMR is not a calorie target — multiply by your activity factor (TDEE) before planning a diet.

Calories Burned Per Hour at Rest
72.4 kcal/hour
Formula Used (Mifflin-St Jeor)
10 × 77.1kg + 6.25 × 178cm − 5 × 30 + 5 = 1,737
Mifflin-St Jeor BMR
1,737 kcal/day
Harris-Benedict BMR
1,804 kcal/day
Katch-McArdle BMR
1,702 kcal/day
Reference Floor (BMR)
Eating below 1,737 kcal/day for long stretches is not advised without medical supervision

The formula

Mifflin-St Jeor: BMR = 10W + 6.25H − 5A + S | Katch-McArdle: BMR = 370 + 21.6 × LBM

W
Weight (kg)
H
Height (cm)
A
Age
S
Sex Constant
LBM
Lean Body Mass

Worked example — Age 30 years, Weight 170, Height — Feet 5 ft, Height — Inches 10 in

BMR — Mifflin-St Jeor = 1,737 kcal/day

Full explanation ↓

How BMR Calculator Works

Mifflin-St Jeor: BMR = 10W + 6.25H − 5A + S | Katch-McArdle: BMR = 370 + 21.6 × LBM

BMR is the number of calories your body burns at complete rest to sustain basic physiological functions. It is a useful floor to keep in mind for your caloric needs — long stretches of eating well below it, without medical supervision, are not advised.

W
Weight (kg) — Total body weight in kilograms.
H
Height (cm) — Height in centimeters.
A
Age — Age in years — BMR decreases ~2% per decade after age 20.
S
Sex Constant — +5 for males, −161 for females (Mifflin-St Jeor).
LBM
Lean Body Mass — Total weight minus fat mass. Used by Katch-McArdle for more precision.

Source: Mifflin MD, St Jeor ST, et al. "A new predictive equation for resting energy expenditure in healthy individuals", Am J Clin Nutr 1990;51:241–247 (10W + 6.25H − 5A + 5 men / −161 women). Revised Harris-Benedict: Roza AM, Shizgal HM, Am J Clin Nutr 1984;40:168–182. Katch-McArdle: 370 + 21.6 × lean body mass (kg). Accuracy review: Frankenfield D et al., J Am Diet Assoc 2005;105:775–789.

Basal Metabolic Rate (BMR) accounts for 60-75% of total daily calorie burn, far more than physical activity

Worked Examples

Sarah is a 30-year-old woman, 165 cm tall, weighing 65 kg. She wants her resting calorie burn using the recommended Mifflin-St Jeor equation.

Sex = Female · Age = 30 · Height = 165 cm · Weight = 65 kg · Formula = Mifflin-St Jeor

BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161 = 650 + 1,031 − 150 − 161 ≈ 1,370 kcal/day.

Sarah burns about 1,370 calories a day at complete rest. That is her floor, not a diet target — eating below it for long stretches risks muscle loss. To get the calories she actually needs, she multiplies this by an activity factor (her TDEE).

Mark is a 40-year-old man, 180 cm tall, weighing 80 kg, using the same Mifflin-St Jeor equation.

Sex = Male · Age = 40 · Height = 180 cm · Weight = 80 kg · Formula = Mifflin-St Jeor

BMR = 10 × 80 + 6.25 × 180 − 5 × 40 + 5 = 800 + 1,125 − 200 + 5 = 1,730 kcal/day.

The only structural difference from Sarah's calculation is the sex constant (+5 for men instead of −161 for women). That single term is why men of similar size have a higher BMR — it stands in for their typically higher lean mass.

Understanding the Result

BMR is your body's idle fuel consumption — the calories burned for breathing, circulation, cell repair, and temperature regulation while completely at rest. The figure shown as a reference floor is your BMR: eating far below it for long periods risks muscle loss and metabolic adaptation. To calculate how many calories you actually need including activity, multiply BMR by an activity factor to get TDEE. Mifflin-St Jeor (1990) is the most validated for the general population, developed using a sample of 498 healthy adults.

Harris-Benedict (1919, revised 1984) tends to overestimate BMR by 5% or more on average. Katch-McArdle is most accurate for lean athletes with known body fat % because it uses lean body mass rather than total weight — this eliminates the error from estimating BMR for overweight individuals where fat mass inflates the weight-based formulas. BMR naturally declines with age by approximately 2% per decade after age 20, primarily due to sarcopenia (age-related muscle loss).

However, this decline can be significantly slowed with consistent resistance training. Body composition changes explain most of the age-related BMR decrease, not aging itself. Women typically have a 5–10% lower BMR than men of the same age and weight because they carry proportionally more body fat and less muscle mass. The thermic effect of food adds roughly 10% on top of BMR, and physical activity accounts for the rest of total daily energy expenditure.

How to Use

  1. Select your unit system (Imperial or Metric).
  2. Select the BMR formula — Mifflin-St Jeor is recommended for most people.
  3. Enter your sex, age, weight, and height.
  4. Optionally enter body fat % for Katch-McArdle or cross-formula comparison.
  5. The formula line shows the exact math so you can verify the calculation.

Quick Reference

Mifflin-St Jeor (men)10W + 6.25H − 5A + 5
Mifflin-St Jeor (women)10W + 6.25H − 5A − 161
BMR share of TDEE~60–75% for most people

Frequently Asked Questions

What is the most accurate BMR formula?
Mifflin-St Jeor is most accurate for the general population. Katch-McArdle is more accurate for lean athletes if you know your body fat percentage. Harris-Benedict often overestimates by 5%.
Can I eat at my BMR to lose weight?
It is possible but usually not advisable. Eating at or near BMR is a very large deficit for most people (TDEE is typically 20–90% higher than BMR) and may cause muscle loss, nutrient shortfalls and rebound weight gain. Very-low-calorie diets (roughly under 800 kcal/day) require medical supervision. A safer deficit is TDEE minus 250–500 calories.
Does BMR decrease with age?
Yes. BMR drops approximately 2% per decade after age 20, primarily due to loss of muscle mass (sarcopenia). Resistance training is the most effective way to preserve metabolic rate as you age.
Does the time of day affect my BMR measurement?
Yes. BMR is lowest during sleep and early morning hours (circadian nadir around 4 AM), and peaks in the late afternoon/early evening. Clinical BMR measurements are typically taken first thing in the morning after an 8-hour fast and 30 minutes of complete rest to standardize conditions. For practical purposes, your TDEE calculation already accounts for daily variations.
How does body composition affect BMR accuracy?
Body composition is the single biggest factor affecting BMR accuracy. Two people of the same age, sex, weight, and height can have BMRs differing by 500+ kcal/day if one is muscular and the other has high body fat. Muscle tissue burns ~6 kcal/lb/day at rest, while fat tissue burns only ~2 kcal/lb/day. This is why Katch-McArdle (which uses lean body mass) is more accurate for individuals who know their body fat percentage.

Common Uses

  • •Weight management planning — use BMR as the baseline for calculating TDEE and setting calorie targets for weight loss, gain, or maintenance with an appropriate deficit or surplus
  • •Nutrition program design — bodybuilders, athletes, and dietitians use BMR to establish the minimum safe caloric intake before adding activity and thermic effect adjustments
  • •Metabolic health assessment — compare BMR formula results to identify metabolic adaptations from prolonged dieting or to assess how body composition changes affect resting energy expenditure
  • •Clinical nutrition — healthcare providers use BMR equations for parenteral nutrition dosing, metabolic monitoring, and estimating energy needs in hospitalized patients

Pro Tips

  • →BMR is calories burned at complete rest. Multiply it by an activity factor (1.2 sedentary up to 1.9 athlete) to get your TDEE — the number you actually plan meals around.
  • →Mifflin-St Jeor is the most accurate equation for the general population. Harris-Benedict tends to read about 5% high; only use Katch-McArdle if you know your body-fat percentage.
  • →Don't eat far below your BMR for extended periods — it drives muscle loss and metabolic slowdown rather than sustainable fat loss.
  • →Recalculate after every ~10 lb (4–5 kg) of weight change; your BMR falls as you get lighter.

Limitations to Know

  • •The equations estimate population averages — an individual's true BMR can vary by roughly ±10% due to genetics, hormones, and body composition.
  • •Weight-based formulas don't see muscle mass directly, so two people of identical weight and height can have meaningfully different real BMRs.
  • •Estimates are not validated for the severely obese, very lean athletes, children, or pregnant or breastfeeding people — use Katch-McArdle or clinical measurement instead.

Sources

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Cite this calculator

TheCalcUniverse. "Basal Metabolic Rate (BMR) Calculator — Mifflin-St Jeor." TheCalcUniverse, 2026, https://thecalcuniverse.com/health/bmr-calculator/. Accessed October 25, 2026.

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