How to Calculate BMR: Your Complete Guide

If you want to learn how to calculate bmr, the good news is that the math takes about two minutes. You need four numbers: weight, height, age, and sex. Plug them into one formula and you get your basal metabolic rate, the calories your body burns at complete rest.

That one number is the starting point for almost every calorie plan. This guide shows you the two formulas that matter, works through a full example for a man and a woman, and turns the result into a daily calorie target you can actually use. By the end, you will know how to calculate bmr for yourself and for anyone else.

Quick Answer: How to Calculate BMR?

The most accurate formula for most people is Mifflin-St Jeor. Here it is, for men and women:

Men: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) + 5

Women: BMR = (10 x weight in kg) + (6.25 x height in cm) – (5 x age in years) – 161

The result is calories per day. A 30 year old man who weighs 80 kg and is 180 cm tall has a BMR of about 1,780 calories. A 30 year old woman who weighs 65 kg and is 165 cm tall has a BMR of about 1,370 calories. The worked math for both is below, and it shows exactly how to calculate bmr by hand. If you want to skip the arithmetic, our BMR calculator does it instantly. This formula comes from the original 1990 study by Mifflin and colleagues, published in the American Journal of Clinical Nutrition (Mifflin et al., PubMed).

What Is BMR?

BMR stands for basal metabolic rate. It is the calories your body needs to keep you alive at complete rest: breathing, circulation, body temperature, brain activity, cell repair, and organ function. It is your energy bill for doing nothing at all.

For most people, BMR accounts for roughly 60 to 70 percent of all calories burned in a day. The rest comes from digesting food, moving around, and exercise. If you know your BMR, you know the floor of your calorie needs. Everything else is added on top of it. That is why learning how to calculate bmr is the first skill in any calorie plan.

Two terms get confused with BMR. Resting metabolic rate, or RMR, is measured under slightly less strict conditions and usually comes out about 10 percent higher. Basal energy expenditure, or BEE, is an older name for the same idea. All three point at the same thing: your resting burn.

How to Calculate BMR With the Mifflin-St Jeor Formula?

The Mifflin-St Jeor equation is the default recommendation of most dietitians today. The original study measured resting energy expenditure by indirect calorimetry in 498 healthy adults. It has held up better than the older Harris-Benedict equation, which tends to overestimate by about 5 percent.

Here is how to calculate bmr with it, step by step:

1. Weigh yourself in kilograms. If your scale shows pounds, divide by 2.2. A weight of 176 pounds is 80 kg.
2. Measure your height in centimeters. If you measure in inches, multiply by 2.54.
3. Take your age in years.
4. Put the numbers into the formula for your sex: weight term, plus height term, minus age term, plus or minus the sex constant.

The sex constant is the only difference between the two versions. Men add 5. Women subtract 161. That gap of 166 calories reflects the average difference in body composition between men and women at the same size. Once you know how to calculate bmr with these four inputs, the rest of this guide is about using the number well.

Worked Example: How to Calculate BMR for a Man and a Woman

Here is the full math for two people, using both formulas, so you can check every step of how to calculate bmr.

Example 1: A 30 year old man, 80 kg, 180 cm

Mifflin-St Jeor:

• Weight term: 10 x 80 = 800
• Height term: 6.25 x 180 = 1,125
• Age term: 5 x 30 = 150
• BMR = 800 + 1,125 – 150 + 5 = 1,780 calories per day

Revised Harris-Benedict:

• Weight term: 13.397 x 80 = 1,071.76
• Height term: 4.799 x 180 = 863.82
• Age term: 5.677 x 30 = 170.31
• BMR = 1,071.76 + 863.82 – 170.31 + 88.362 = 1,853.63, about 1,854 calories per day

Harris-Benedict gives a number about 74 calories higher, roughly 4 percent.

Example 2: A 30 year old woman, 65 kg, 165 cm

Mifflin-St Jeor:

• Weight term: 10 x 65 = 650
• Height term: 6.25 x 165 = 1,031.25
• Age term: 5 x 30 = 150
• BMR = 650 + 1,031.25 – 150 – 161 = 1,370.25, about 1,370 calories per day

Revised Harris-Benedict:

• Weight term: 9.247 x 65 = 601.055
• Height term: 3.098 x 165 = 511.17
• Age term: 4.330 x 30 = 129.9
• BMR = 601.055 + 511.17 – 129.9 + 447.593 = 1,429.918, about 1,430 calories per day

Again, Harris-Benedict lands about 60 calories higher. The pattern holds: Harris-Benedict runs a little hot, Mifflin-St Jeor runs closer to lab measurements. If you want to know how to calculate bmr for a woman specifically, this is the example to copy, since many guides only show a male example.

Example 3: From pounds and inches

A 35 year old man weighs 176 pounds and is 5 feet 11 inches tall. Convert first: 176 / 2.2 = 80 kg, and 71 inches x 2.54 = 180.34 cm, which we round to 180 cm. Then Mifflin-St Jeor gives 800 + 1,125 – 175 + 5 = 1,755 calories per day. Converting first is the step most people skip, and it is the most common reason hand calculations go wrong. These three examples cover how to calculate bmr in metric, for both sexes, and from imperial units.

How Does the Harris-Benedict Formula Compare?

The Harris-Benedict equation is the older way to learn how to calculate bmr, published in 1919 and revised in 1984 with new data. The revised version is the one worth using:

Men: BMR = 88.362 + (13.397 x weight in kg) + (4.799 x height in cm) – (5.677 x age in years)

Women: BMR = 447.593 + (9.247 x weight in kg) + (3.098 x height in cm) – (4.330 x age in years)

	Mifflin-St Jeor	Revised Harris-Benedict
Published	1990	1984 (original 1919)
Accuracy	Usually within about 10 percent of lab measurement	Tends to overestimate by about 5 percent
Ease of use	Simple round numbers	Messy decimals
Best for	Most adults, general use	Older adults, clinical settings that still use it

Which one should you use? For most people, Mifflin-St Jeor. It is simpler, it is built on newer data, and it matches lab measurements more closely on average. The difference between the two is usually 50 to 100 calories. Pick one, use it consistently, and adjust based on real results.

One more formula is worth knowing. Katch-McArdle uses lean body mass instead of total weight: BMR = 370 + (21.6 x lean mass in kg). If you know your body fat percentage, it can beat both formulas above, because it counts muscle and ignores fat.

What Is the Difference Between BMR and TDEE?

BMR is only the resting part of your burn. TDEE, total daily energy expenditure, is the full picture: BMR plus digestion, daily movement, and exercise. This distinction confuses most people, and it is why two calculators can give very different numbers for the same person. Once you know how to calculate bmr, multiply it by an activity factor to get TDEE:

Activity level	Multiplier	What it means
Sedentary	1.2	Desk job, little or no exercise
Lightly active	1.375	Light exercise 1 to 3 days a week
Moderately active	1.55	Moderate exercise 3 to 5 days a week
Very active	1.725	Hard exercise 6 to 7 days a week
Extra active	1.9	Very hard training, physical job, or training twice a day

Using our examples: the man with a BMR of 1,780 who trains moderately has a TDEE of 1,780 x 1.55 = 2,759 calories. The woman with a BMR of 1,370 who is lightly active has a TDEE of 1,370 x 1.375 = 1,883.75, about 1,884 calories. Most people overestimate their activity level, so when in doubt, pick the lower multiplier. A desk job plus three gym sessions is lightly active, not very active. Our guide to what is TDEE explains the full breakdown, and our BMR vs TDEE comparison walks through which number to use for each goal.

The key rule: never eat at your BMR to lose weight. Eating at that level while also moving and exercising creates a deficit that is too steep for most people. Set your deficit or surplus from TDEE instead.

What Is a Normal BMR by Age and Sex?

There is no single normal BMR, since it depends on size. But the pattern by age and sex is consistent, and this table shows it for two fixed body sizes. It also works as a check on how to calculate bmr for your own age and size. The male row is a man of 70 kg and 175 cm. The female row is a woman of 60 kg and 163 cm. All values use Mifflin-St Jeor.

Age	Men, 70 kg, 175 cm	Women, 60 kg, 163 cm
25	1,674	1,333
35	1,624	1,283
45	1,574	1,233
55	1,524	1,183
65	1,474	1,133

Two patterns stand out. First, men run about 300 to 350 calories higher than women at a similar size, because of greater average muscle mass. Second, BMR falls by about 50 calories per decade at fixed weight and height. In real life the drop is often larger, because people also lose muscle as they age. Use this table as an age BMR chart and a sanity check. If your number is far outside the range for your age and size, recheck your inputs. The most common errors are entering weight in pounds instead of kilograms, and height in inches instead of centimeters.

How Do You Use BMR to Set Your Calories?

BMR itself is not a calorie target. It is the input to one, and knowing how to calculate bmr is only step one of three:

1. Calculate your BMR with the Mifflin-St Jeor formula.
2. Multiply by your activity factor to get your TDEE, your maintenance calories.
3. Adjust for your goal: subtract for fat loss, add for muscle gain, keep it level for maintenance.

Goal	Calorie target	Example, man with TDEE 2,759
Fat loss	TDEE minus 300 to 500	2,259 to 2,459
Maintenance	TDEE	2,759
Muscle gain	TDEE plus 200 to 300	2,959 to 3,059

For the woman with a TDEE of 1,884, fat loss means roughly 1,384 to 1,584 calories, and muscle gain means roughly 2,084 to 2,184 calories. These are starting estimates. Track your weight for two to three weeks, then adjust by 100 to 200 calories if the trend is wrong. The formula gets you close, and your own data finishes the job.

Once you have your calorie target from learning how to calculate bmr, the next step is splitting it into protein, carbs, and fat. Our guide to how many calories a day shows how to pick a target for your goal, and our guide to how to calculate macros turns that target into grams of each nutrient.

Should I Eat My BMR Calories to Lose Weight?

No. Eating only your BMR while also moving and exercising creates a deficit that is too steep for most people, and it is hard to sustain. It can also cost muscle, which lowers BMR further. Instead, calculate your TDEE from your BMR, then subtract a moderate 300 to 500 calories.

What Affects Your BMR?

Your BMR is not fixed. None of these factors change how to calculate bmr, but they change the number you get and how much to trust it:

• Muscle mass. Muscle costs more energy to maintain than fat. Two people at the same weight can have BMRs hundreds of calories apart if one is muscular and the other is not. This is the biggest factor you can change.
• Body size. A larger body has more tissue to maintain, so it burns more at rest.
• Age. BMR declines about 1 to 2 percent per decade after early adulthood, mostly because muscle mass falls.
• Sex. Men typically have higher BMRs than women at the same weight, because of greater average muscle mass.
• Hormones. Thyroid hormones are the main lever. An overactive thyroid raises BMR, and an underactive thyroid lowers it.
• Illness and fever. Fever raises BMR, roughly 7 percent for every 1 degree Fahrenheit rise in body temperature.
• Pregnancy and breastfeeding. BMR rises to support the baby, and stays elevated while breastfeeding.
• Dieting. Long, aggressive deficits lower BMR, because the body adapts by becoming more efficient. This is one reason crash diets stall.
• Genetics. Some people run naturally hotter or cooler than average. Genetics sets a range, not a destiny.

Can You Increase Your BMR?

Honestly, only a little, and the levers are slow. No food, supplement, or hack raises BMR by a meaningful amount. The real ways:

Build muscle. This is the only lever that matters much. Each kilogram of muscle adds roughly 13 calories per day to your BMR. Five kilograms of added muscle is about 65 extra calories a day, every day, plus the calories burned in the training itself. Strength training twice a week is the highest return habit for BMR.

Stay active. Exercise does not raise BMR much directly, but it protects muscle, and the calories burned during activity add to TDEE.

Eat enough protein. Protein has the highest thermic effect of the three macros. Your body spends roughly 20 to 30 percent of protein calories on digestion, versus 5 to 10 percent for carbs and 0 to 3 percent for fat.

Avoid crash diets. Severe deficits cost muscle, and lost muscle lowers BMR. A moderate deficit with enough protein protects muscle and keeps BMR steadier.

What does not work: fat burners, detox teas, and eating six small meals instead of three. Meal frequency does not change total daily burn in any meaningful way. No shortcut changes the formula. Learning how to calculate bmr stays the same, only your inputs change as your body changes.

What Are the Limits of BMR Formulas?

BMR formulas are estimates, not measurements. Mifflin-St Jeor is usually within about 10 percent of a lab measurement, which means a true BMR of 1,700 could come out as 1,530 to 1,870. That range is normal, and it is why you should always adjust based on real weight trends.

The formulas also have specific blind spots:

• Very muscular people. The formulas use total weight, so they underestimate BMR for lifters with high muscle mass. Katch-McArdle is better here.
• Obesity. Accuracy drops at very high body weights, because the formulas assume an average body composition.
• Medical conditions. Thyroid disorders and some medications change BMR beyond what any formula predicts. If you have a condition that affects metabolism, treat the formula as a rough guide and talk to your doctor.
• Pregnancy. Standard formulas do not account for pregnancy. Energy needs rise, especially in the second and third trimesters.
• Children and teens. These formulas are built for adults. Children need age specific methods.
• Metabolic adaptation. After long dieting, BMR can sit below the predicted value for months. This is the adaptation behind plateaus.

These limits do not change how to calculate bmr, but they change how much to trust the result. The lab method, indirect calorimetry, measures the oxygen you consume and the carbon dioxide you produce while resting. It is more precise, but it is expensive and hard to access.

Can I Use a BMR Calculator if I Am Pregnant or Have a Thyroid Condition?

Standard BMR formulas do not account for pregnancy or thyroid disorders, so treat the number as a rough starting point only. Pregnancy raises energy needs, especially in the second and third trimesters. Thyroid conditions can raise or lower BMR well beyond what any formula predicts. If either applies to you, ask your doctor for a personal target.

Your 3-Step BMR Plan

Here is the whole process in three steps, from learning how to calculate bmr to acting on the number.

1. Calculate your BMR with Mifflin-St Jeor, using kilograms and centimeters. Round to the nearest 10 calories. False precision helps no one.
2. Multiply by your honest activity factor to get TDEE, then set your goal target: minus 300 to 500 for fat loss, level for maintenance, plus 200 to 300 for muscle gain.
3. Track your weight for two to three weeks. If the trend matches your goal, keep the numbers. If not, adjust by 100 to 200 calories and repeat.

If you also want to know how to calculate bmr for someone else, a parent or a training partner, the same steps work. Just use their numbers. And if you want the number without the arithmetic, our BMR calculator runs the same formula and adds the activity multipliers automatically.

How Often Should I Recalculate My BMR?

Once you know how to calculate bmr, recalculating takes two minutes. Recalculate when your weight changes by about 5 kg, when your activity level changes, or every three to six months as a routine check. BMR falls as you lose weight, because a smaller body costs less energy to maintain. If you keep eating for your old weight, your deficit quietly disappears.

Frequently Asked Questions