BMR Calculator: Your Basal Metabolic Rate

What is basal metabolic rate (BMR)?

Your basal metabolic rate is the number of calories your body burns at complete rest to keep you alive, covering things like breathing, circulation, and brain function.

Think of BMR as your body's idle fuel cost, before any movement, exercise, or digestion. It usually makes up 60 to 70% of the calories you burn each day, which is why it is the foundation of any calorie or weight loss plan.

BMR vs RMR vs TDEE

BMR is calories burned at rest, RMR is nearly the same measured less strictly, and TDEE is your full daily burn including activity, which is the number you should base your diet on.

BMR calculator for weight loss

To lose weight, eat 300 to 500 kcal below your TDEE, not below your BMR, which gives steady fat loss while protecting your muscle.

A 500 kcal daily deficit gives roughly 0.5 kg of fat loss per week. The calculator above shows your exact weight loss, maintenance, and muscle gain calories once you enter your details.

How many calories do I burn at rest?

The calories you burn at rest are your BMR, typically 1,300 to 1,600 kcal a day for women and 1,600 to 2,000 kcal a day for men.

Most of this resting burn comes from your organs. The liver, brain, muscles, and kidneys together account for more than 70% of the energy your body uses while doing nothing at all. Enter your details above to see your own number.

How to calculate BMR

Calculate BMR with the Mifflin-St Jeor equation, which uses your weight, height, age, and sex.

Which BMR formula is most accurate?

The Mifflin-St Jeor equation is the most accurate for most adults, while Katch-McArdle is best if you know your body fat percentage.

BMR calculator for men

Men usually have a higher BMR than women of the same size because they carry more muscle and less essential body fat.

BMR calculator for women

Women have a slightly lower BMR than men of the same size, reflected by the -161 term in the female Mifflin-St Jeor equation.

Pregnancy, menopause, and thyroid conditions can shift your actual BMR beyond what any formula predicts.

What is a normal or average BMR?

A normal BMR is roughly 1,300 to 1,600 kcal for younger women and 1,600 to 2,000 kcal for younger men, falling gradually with age.

BMR by age: how much it actually falls

The Mifflin-St Jeor equation subtracts 5 kcal for every year of age, so BMR drops about 50 kcal per decade if your weight and height stay the same. Between 20 and 60 that is roughly 200 kcal a day.

Both tables below hold weight and height fixed so you can see the age effect on its own. The first is a woman of 5'4" and 150 lb, the second a man of 5'10" and 180 lb.

Worth reading that carefully, because the usual conclusion drawn from it is wrong. The formula assumes the decline is automatic, but a good share of what it models is muscle quietly lost over decades rather than age itself. A 60 year old who has kept their muscle mass often measures well above the number in this table. That is also why the equation subtracts a flat 161 kcal for women: it is standing in for a typical difference in body composition, not making a claim about individual metabolism.

How to increase your metabolism

The most effective way to increase your BMR is to build muscle with resistance training, supported by enough protein, sleep, and daily movement.

Common BMR mistakes

The most common BMR mistakes are dieting to your BMR instead of your TDEE, and not recalculating after you lose weight.

Why Your BMR Can Fall During GLP-1 Weight Loss

If you are on a GLP-1 like Ozempic, Wegovy, Mounjaro or Zepbound and the scale has slowed down, a falling BMR is often part of the story, and it usually does not mean the medication has stopped working.

Quick refresher. Your BMR is what your body burns at rest just to keep the lights on, and it is not a fixed number. It moves with your size and your muscle. When you lose weight, there is simply less of you to power, so your BMR comes down with it. A smaller body burns fewer calories, even doing nothing all day.

Then there is the part that catches a lot of people off guard, called metabolic adaptation (you will also see it called adaptive thermogenesis). When you spend a long stretch eating well under what you used to, your body reads that as food being scarce and quietly dials down how much energy it spends. It is a survival feature, not a flaw. Hormones shift, and you tend to move a little less without realising it, less fidgeting, fewer trips up the stairs, that kind of thing. The result is that your resting burn can land lower than a formula would predict for your new weight.

Put those two together and you get the pattern almost everyone hits. The first few weeks fly by, then loss slows even though you feel like you are doing everything the same. On a GLP-1 this can be unsettling, because it is easy to assume the drug gave up on you. Usually it did not. Your appetite is still suppressed and you are still eating in a deficit. The deficit just got smaller, because the gap between what you eat and what you burn narrowed as your BMR dropped. That is arithmetic, not failure.

The good news is you have real say over how far your BMR falls, and it comes down to protecting the tissue that burns the most at rest, which is muscle. During fast weight loss, and especially on a GLP-1 when you are eating a lot less, some of what you lose can be muscle rather than fat, and losing muscle is exactly what drags your resting burn down even further. Two habits blunt that.

None of this is a reason to panic. It just means your BMR from six weeks ago is not your BMR today, so it is worth running the calculator again at your current weight and rebuilding your targets from the fresh number. And if the stall drags on and you want to check whether it looks normal or is worth raising with your prescriber, that is exactly what the GLP-1 plateau analyzer is for. Your clinician knows your full picture, so always loop them in before you change your dose or your plan.

Frequently asked questions