OnSumoTools

BMR Calculator

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

Unit system

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 does the BMR Calculator work step by step?

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.

What does a typical BMR Calculator result look like?

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.

  • Can I raise my BMR?

    Yes, to a degree. Building muscle through resistance training increases lean mass, which raises your resting calorie burn over time. Crash dieting has the opposite effect, lowering BMR as the body adapts to lower intake. Age-related BMR decline is real but slower than most people assume.

Related tools

What BMR is

Basal Metabolic Rate is the number of calories your body burns at complete rest. Breathing, circulation, keeping cells working, staying warm. If you lay in bed all day and didn't move, that's roughly what you'd use.

It usually makes up the biggest share of what you burn in a day. That makes it the starting point for any calorie plan, whether you want to lose weight, hold steady or gain.

Three equations, one tool

The calculator offers the Mifflin-St Jeor equation, the Harris-Benedict equation and Katch-McArdle. They all estimate the same thing in different ways.

Mifflin-St Jeor is the one most dietitians favor today. It was published in 1990 and tends to be closer for modern populations than the older Harris-Benedict, which dates from the early 1900s and was revised later. Both use sex, age, weight and height.

Katch-McArdle works differently. It uses lean body mass, so it needs your body fat percentage. If you know that number, it can be more accurate for very lean or very muscular people. If you don't, stick with Mifflin-St Jeor.

Turning BMR into a daily target

BMR isn't what you eat. You move, work and exercise, and that burns extra. Multiply BMR by an activity factor to get total daily energy use. That's the figure you build a plan around.

The calorie calculator on this site does that step for you and lets you set a goal.

Can you raise it?

A little. Muscle tissue burns more at rest than fat does, so building muscle nudges BMR up. The effect is real but modest. Weight also plays a part, since a larger body needs more energy.

Beware of products that promise to speed up your metabolism. Most do very little. Sleep, protein and strength training are far better bets. And crash dieting can lower your rate as your body adapts, which makes the next attempt harder.

How accurate is it?

It's an estimate. Real people vary by a couple hundred calories either direction from any formula. Treat the result as a starting line. Eat at that level for two to three weeks, watch your weight trend and adjust.

Not medical advice. If you have a medical condition, are pregnant or are planning a major change in diet, see a doctor or dietitian. Your inputs stay in your browser.

What the number is, and isn't

Your BMR is the energy your body burns at complete rest, to keep your heart beating, your lungs working and your organs running. For most adults that makes up well over half of daily energy use. It's an estimate from a formula, not a lab measurement.

Two people with the same height, weight and age can differ by a couple of hundred calories a day. Muscle mass, genetics, hormones and health conditions all play a part, and none of those appear in a basic formula.

Treat the figure as a starting point. Eat near it for two weeks, track your weight, and adjust.

From BMR to daily needs

Multiply BMR by an activity factor to get total daily energy expenditure, or TDEE. A desk job with little exercise sits near 1.2. Light exercise a few times a week is about 1.375. Heavy training most days can reach 1.7 or more.

People overrate their activity almost every time. If you're unsure between two levels, pick the lower. A fitness tracker that claims a big burn is usually generous too.

To lose weight slowly, eating roughly 300 to 500 calories under TDEE is a common range. To gain, go the same distance above.

Common mistakes

Eating below your BMR for long periods is a bad idea. It can cost you muscle, energy and mood, and it often backfires with rebound eating.

Don't change the numbers after one day. Weight swings by a kilogram or more from water and food in the gut. Look at weekly averages instead.

This tool is a guide and not medical advice. If you have a condition, are pregnant or are under 18, talk to a doctor or dietitian first.