BMR Calculator

This BMR calculator estimates how many Calories your body burns at complete rest, and how many you'd need each day at different activity levels. Enter your age, sex, height and weight, then press Calculate.

What your BMR tells you

Your basal metabolic rate is the floor of your daily energy use: roughly what you'd burn lying in bed all day without moving. It's usually the biggest part of the day's total, around 60–70% of it according to the International Society of Sports Nutrition's position stand on diets and body composition. Walking, working, exercise and digesting food all come on top.

A common mistake is to treat BMR as the amount to eat. It isn't: it leaves out everything you do while awake. To estimate what keeps your weight steady, multiply your BMR by an activity factor. The calculator does this in the table under the answer.

BMR formulas

Weight is in kilograms, height in centimeters and age in years. To convert, multiply pounds by 0.4536 and inches by 2.54.

Which formula to use

Mifflin-St Jeor, unless you have a reason not to. It was fitted to measurements of 498 healthy adults aged 19 to 78 (Mifflin and colleagues, 1990). A 2005 review for the American Dietetic Association found it predicted resting rate within 10% of the measured value in more people, of normal weight or with obesity, than the three other equations it compared, which included the original Harris-Benedict. Katch-McArdle wasn't part of that review.

Harris-Benedict dates from 1919 and was refitted in 1984 (Roza and Shizgal). In Mifflin's study, the original 1919 version overestimated measured resting rate by about 5%. In both examples on this page, the revised version also comes out a little higher, by about 50–60 Calories. Use it if a diet plan or coach asks for it, so your numbers match theirs.

Katch-McArdle ignores age and sex and works only from lean mass. Use it if you know your body fat from a DEXA scan or another lab test, especially if you carry a lot of muscle, because the other two equations only see total weight, not how much of it is muscle. Calipers and smart scales can be several points off, and a 5-point error moves the answer by roughly 5%.

Worked examples

Example 1: Mifflin-St Jeor in US units. A 35-year-old woman is 5 ft 5 in tall and weighs 150 lb. Her height is 65 in × 2.54 = 165.1 cm and her weight is 150 × 0.4536 = 68.04 kg.

The revised Harris-Benedict gives her 1,437, about 60 more. If she exercises 3 to 5 days a week, she'd maintain her weight on about 1,376 × 1.55 = 2,133 Calories a day.

Example 2: one man, all three formulas. A 30-year-old man is 175 cm tall, weighs 70 kg and has 15% body fat.

Here the three answers land within 50 Calories of each other because, at 15% body fat, his lean mass is about what the weight-based formulas expect for his size. At 25% body fat, Katch-McArdle would give 370 + 21.6 × 52.5 = 1,504, about 150 to 190 below the other two. The further your build is from average, the more the formulas disagree.

Activity factors

These multipliers are a long-standing rule of thumb used with all three formulas, not a measurement of you. If you're between two levels, pick the lower one: it's easy to count a short walk as exercise, and the weight check below will show if you guessed low.

The result is a starting estimate. If your weight holds steady for three or four weeks at that intake, it's about right for you. If you're gaining, eat 100–200 Calories a day less; if you're losing when you meant to hold steady, eat 100–200 more. Check again after another few weeks.

Eating less to lose weight

A common starting point is about 500 Calories a day below your maintenance figure, but check where that leaves you. The woman in Example 1, exercising 3 to 5 days a week, maintains on 2,133, so a 500 cut gives 1,633, about 23% less (the percentage calculator works out shares like this). If she were sedentary, she'd maintain on about 1,376 × 1.2 = 1,652, and a 500 cut would leave 1,152: a cut of about 30% that's below even her BMR. In that case use a smaller cut, or talk to a doctor or dietitian before eating that little for long.

How age changes BMR

With height and weight held the same, Mifflin-St Jeor takes off 5 Calories a day for every year of age. That comes from averaging the adults in its 1990 study, not from tracking anyone over time. A large 2021 study by Pontzer and colleagues found that energy use, adjusted for lean mass, held steady from about 20 to 60 and declined after 60, so read this table as what the formula does, not a forecast. Here's the woman from Example 1 at different ages:

Limits of a BMR estimate

• It's an average, not a measurement. Even with the best equation, the 2005 review found a noticeable share of people more than 10% away from their measured rate. Only a lab test (indirect calorimetry) measures your own.
• Who it fits. The equations were built from healthy adults. They're rougher for teenagers and people over 80, and they can't allow for pregnancy, breastfeeding, thyroid conditions, recent illness or medicines that affect metabolism.

Last updated: November 9, 2026