BMR Calculator

Use our free bmr calculator to find your basal metabolic rate in seconds. Enter your age, height, weight, and gender to get your BMR from the two most trusted formulas, Mifflin-St Jeor and Harris-Benedict, side by side.

Calculate Your BMR

Gender

What Is BMR?

BMR stands for basal metabolic rate: the number of calories your body burns at complete rest to keep you alive. Breathing, circulating blood, maintaining body temperature, growing cells, keeping your brain running, all of it is powered by your BMR. It is the largest slice of your daily calorie burn, typically 60 to 70 percent of your total.

One nuance worth knowing: BMR is technically measured under strict laboratory conditions (fully rested, fasted, motionless). Resting metabolic rate (RMR) is a looser measure that includes minimal daily activity and runs about 10 percent higher. In practice, online calculators labeled “BMR” estimate something closer to RMR, which is actually more useful for planning your calories. The difference is small enough that it does not change any decision you would make.

How This BMR Calculator Works

This bmr calculator runs the two most trusted BMR formulas and shows you both, so you can see the range instead of a single fragile number. The Mifflin-St Jeor equation is the modern standard, recommended in nutrition practice and considered the most accurate for the general population. The Harris-Benedict equation (revised version) is the classic alternative, still widely used in clinical settings.

  • Mifflin-St Jeor, men: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) + 5
  • Mifflin-St Jeor, women: BMR = 10 x weight (kg) + 6.25 x height (cm) – 5 x age (years) – 161
  • Harris-Benedict (revised), men: BMR = 88.362 + 13.397 x weight (kg) + 4.799 x height (cm) – 5.677 x age (years)
  • Harris-Benedict (revised), women: BMR = 447.593 + 9.247 x weight (kg) + 3.098 x height (cm) – 4.330 x age (years)

Both formulas in this bmr calculator take the same four inputs, age, gender, height, and weight, and both output a daily calorie number. For background on how these equations were developed and validated, see the basal metabolic rate reference on Wikipedia.

Mifflin-St Jeor vs Harris-Benedict

Mifflin-St JeorHarris-Benedict (revised)
Developed19901919, revised 1984
Accuracy vs lab measurementWithin about 10% for most peopleWithin about 15%, tends to run slightly high
Best forGeneral healthy adultsClinical settings, older literature
Our default test (30y male, 175cm, 75kg)1,699 kcal/day1,763 kcal/day

The two formulas usually land within 50 to 100 kcal of each other, which is why showing both is useful: your true BMR almost certainly sits somewhere in that range. A third formula, Katch-McArdle (BMR = 370 + 21.6 x lean body mass in kg), can beat both, but only if you know your body fat percentage accurately, which most people do not.

What Affects Your BMR

  • Muscle mass. The biggest lever you control. Muscle burns roughly 6 kcal per pound per day at rest, versus about 2 for fat. Two people at the same weight can have BMRs hundreds of calories apart.
  • Body size. Larger bodies cost more energy to maintain, which is why taller and heavier people have higher BMRs.
  • Age. BMR declines about 1 to 2 percent per decade after your 20s, mostly because muscle mass declines. It is not aging itself doing the damage.
  • Sex. Men average higher BMRs than women at the same stats, driven by greater muscle mass. The formulas bake in a 166 kcal difference.
  • Hormones. Thyroid hormones set the pace of your metabolism; hypothyroidism can drag BMR down noticeably and is worth checking if your numbers look oddly low.
  • Dieting history. Long, aggressive calorie restriction can temporarily suppress BMR through adaptive thermogenesis. Your body gets efficient at surviving on less, which is one reason crash diets backfire.

Can You Increase Your BMR?

Honestly, only one lever matters much: build muscle. Strength training 2 to 4 times a week gradually raises your BMR because every kilogram of new muscle burns extra calories around the clock. Eating enough protein supports that process and costs slightly more energy to digest (the thermic effect of food). Staying active through the day, walking, standing, fidgeting, adds meaningful burn too, though technically that is NEAT rather than BMR.

What does not move the needle: caffeine and green tea (tiny, temporary effects), cold exposure (measurable but impractical as a strategy), and “metabolism booster” supplements (no credible evidence). Anyone selling you a big BMR increase without muscle gain is selling something else.

BMR vs TDEE: What’s the Difference?

BMRTDEE
What it measuresCalories burned at complete restTotal calories burned in a full day
Typical share of TDEE60-70%100% (by definition)
Use it forUnderstanding your baseline; never eat below it long-termSetting actual daily calorie targets

BMR is your floor; TDEE is your plan. To turn your BMR into a daily calorie target, multiply it by an activity factor, which is exactly what our TDEE calculator does. A moderately active person multiplies BMR by about 1.55.

Worked Example

Take a 30-year-old man, 175 cm, 75 kg. Mifflin-St Jeor: (10 x 75) + (6.25 x 175) – (5 x 30) + 5 = 750 + 1,093.75 – 150 + 5 = 1,699 kcal/day. Harris-Benedict (revised): 88.362 + (13.397 x 75) + (4.799 x 175) – (5.677 x 30) = 1,763 kcal/day. The two methods differ by 64 kcal, and his true BMR sits somewhere in that tight range. At moderate activity (x1.55), his TDEE would be about 2,633 kcal/day.

What To Do With Your BMR Number

Your BMR alone does not tell you how much to eat; it tells you where your floor is. Next steps: get your full daily burn with the TDEE calculator, set a daily target with the calorie calculator, plan fat loss safely with the calorie deficit calculator, and protect your muscle with the right intake from the protein calculator.

Frequently Asked Questions

What is a good BMR?

There is no single good number; BMR scales with your size. Most adults fall between 1,200 and 2,400 kcal/day. What matters is the trend as your body composition changes, not hitting a magic number.

Which BMR formula is most accurate?

Mifflin-St Jeor, for most adults. It was built on modern population data and is the standard in nutrition practice, accurate within about 10%. Harris-Benedict (revised) is close but tends to run slightly high. If you know your body fat percentage, Katch-McArdle can beat both.

What is the difference between BMR and RMR?

BMR is measured under strict lab conditions (fully rested, fasted, motionless). RMR is looser and includes minimal daily activity, running about 10% higher. Online calculators labeled BMR actually estimate closer to RMR, which is fine for planning calories.

Why is my BMR so low?

Usually body composition: less muscle and a smaller body mean a lower BMR. Age plays a role too, about 1 to 2% decline per decade after your 20s, mostly from muscle loss. Long crash diets can also temporarily suppress it.

Can I eat below my BMR?

Briefly, yes, but not as a lifestyle. Chronically eating below BMR risks muscle loss, hormonal disruption, and rebound hunger. Most guidelines suggest staying above 1,200 kcal/day for women and 1,500 for men unless medically supervised. Use our calorie deficit calculator at https://healthcalculatorhub.com/calorie-deficit-calculator/ to set a safer target.

Does BMR decrease with age?

Yes, roughly 1 to 2% per decade after age 20, driven mostly by gradual muscle loss rather than aging itself. Strength training and enough protein slow this decline significantly.

Why do men have a higher BMR than women?

On average men carry more muscle mass and larger bodies, and muscle burns more calories at rest than fat. The formulas reflect this: at identical height, weight, and age, the male equation adds 166 kcal over the female one.

How can I increase my BMR?

Build muscle with strength training, the only meaningful long-term lever. Eat enough protein, stay active through the day, and avoid crash diets that trigger metabolic slowdown. Caffeine and cold exposure help only trivially.

Other Calculators