What is BMR and why does it matter?

Basal Metabolic Rate is the number of calories your body burns at complete rest to keep basic life functions running, including breathing, blood circulation, and cell production. It typically accounts for 60 to 70 percent of your total daily calorie burn. Knowing your BMR helps you set a calorie floor below which you should not eat for extended periods without medical supervision.

Which BMR equation should I trust?

Mifflin-St Jeor is the most commonly recommended formula for general adults because it has been validated in more recent studies. If you know your body fat percentage, Katch-McArdle is often more accurate because it calculates from lean mass rather than total weight. The tool shows all three so you can compare and use the range rather than a single number.

Why does the Katch-McArdle result require body fat percentage?

The Katch-McArdle formula calculates BMR from lean body mass rather than total weight. Since fat tissue is less metabolically active than muscle, this approach can be more accurate for very lean or very muscular individuals. Without a body fat measurement, the formula cannot separate lean mass from fat mass, so it is only shown when you provide that input.

BMR Calculator

Estimate your Basal Metabolic Rate using three equations side by side: Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle.

SexAge (years)

Unit system

Height (cm)Weight (kg)

Body fat % (optional, for Katch-McArdle)

BMR by equation

Mifflin-St Jeor

1,749 kcal

Harris-Benedict (revised)

1,830 kcal

Katch-McArdle

Enter body fat % to show lean-mass BMR.

BMR equations are population-level estimates. Individual metabolism can vary by 15-20% due to genetics, hormones, and body composition. These results are not medical advice.

How this tool works

Basal metabolic rate (BMR) is the number of calories your body burns at complete rest to sustain vital functions like breathing, circulation, and cell repair. This tool computes BMR using three well-known equations side by side. Mifflin-St Jeor (most validated for general adults): BMR = (10 x weight_kg) + (6.25 x height_cm) - (5 x age) + 5 for men or -161 for women. Revised Harris-Benedict: uses slightly different coefficients derived from a 2001 recalibration of the original 1919 equation. Katch-McArdle: BMR = 370 + (21.6 x lean_mass_kg), which requires body-fat percentage and is often more accurate for athletes because it accounts for lean mass directly. By comparing all three, you can see the range of estimates rather than relying on a single number. Key assumption: these are resting-metabolism estimates only and do not include any physical activity.

Worked example

A 30-year-old man weighing 80 kg at 175 cm tall gets a Mifflin-St Jeor BMR of about 1,749 kcal/day and a Harris-Benedict BMR of about 1,758 kcal/day. If he enters 20% body fat, the Katch-McArdle formula uses his 64 kg of lean mass to produce a BMR of about 1,752 kcal/day. All three estimates cluster close together, giving confidence the true resting metabolism is near 1,750 kcal/day.

Frequently asked questions

What is BMR and why does it matter?
Basal Metabolic Rate is the number of calories your body burns at complete rest to keep basic life functions running, including breathing, blood circulation, and cell production. It typically accounts for 60 to 70 percent of your total daily calorie burn. Knowing your BMR helps you set a calorie floor below which you should not eat for extended periods without medical supervision.
Which BMR equation should I trust?
Mifflin-St Jeor is the most commonly recommended formula for general adults because it has been validated in more recent studies. If you know your body fat percentage, Katch-McArdle is often more accurate because it calculates from lean mass rather than total weight. The tool shows all three so you can compare and use the range rather than a single number.
Why does the Katch-McArdle result require body fat percentage?
The Katch-McArdle formula calculates BMR from lean body mass rather than total weight. Since fat tissue is less metabolically active than muscle, this approach can be more accurate for very lean or very muscular individuals. Without a body fat measurement, the formula cannot separate lean mass from fat mass, so it is only shown when you provide that input.