Mifflin-St Jeor formula: how accurate is your BMR?

The short answer

• 82%

  Of 337 adults got an estimate within 10% of their measured resting energy

• 75%

  Within 10% for people with obesity, compared with 87% for people without

• 498

  Adults whose resting energy was measured to build the formula in 1990

• 1.4–2.4

  Activity factors to multiply your BMR by, from mostly sitting to very active

Key findingMifflin-St Jeor is the best everyday starting point. Still, it misses by more than 10% for about 1 in 5 people. So use it to start, then adjust from what your weight actually does.

What is the Mifflin-St Jeor formula?

Your basal metabolic rate, or BMR, is the energy (calories) your body burns just to keep you alive at rest. It powers your heart, lungs, brain and other organs. For adults, it is about 45–70% of all the calories you burn in a day.

The Mifflin-St Jeor formula estimates your BMR from four things: your weight, height, age and sex. A team led by Mifflin and St Jeor published it in 1990. Dietitians use it often, and so do many calorie calculators.

• Men: 10 × weight in kg + 6.25 × height in cm − 5 × age in years + 5
• Women: 10 × weight in kg + 6.25 × height in cm − 5 × age in years − 161

The answer is in kilocalories (kcal) a day, the “calories” on food labels. For the same weight, height and age, the men’s formula gives 166 kcal a day more.

The researchers measured each person once. Fat-free mass, meaning everything in your body that isn’t fat, was the best single predictor of resting energy. But weight, height, age and sex together did even better, and they are much easier to know.

A worked example

Here is the formula for a woman aged 32 who weighs 68 kg and is 162 cm tall. This is our own calculation, and it matches the example in our calorie deficit calculator.

So her BMR is about 1,370 kcal a day. Now take a man aged 40 who weighs 80 kg and is 178 cm tall. His sum is 800 + 1,112.5 − 200 + 5, or about 1,720 kcal a day.

Is the Mifflin-St Jeor equation accurate?

For most people, it is close. A 2005 review for dietitians compared the four most used formulas. It was a systematic review: a careful review of all the studies on one question. Mifflin-St Jeor came within 10% of measured resting energy in more people than any other formula. Its errors also had the narrowest range.

A 2013 study gives the numbers. A researcher in the US measured the resting energy of 337 adults and compared it with seven formulas. Mifflin-St Jeor was right on average, while most of the others guessed too high. It landed within 10% for 82% of people.

That leaves about 1 in 5 people who are more than 10% off. For the woman above, 10% either way means a true BMR anywhere from about 1,230 to 1,510 kcal a day (our calculation). The formula can’t tell which end she is at.

It also worked less well for some groups. Accuracy was lower in people with obesity, whatever formula was used. The 2005 review also warned that the studies included too few older adults and people from ethnic minorities in the US. For those groups, treat any formula with extra care.

Mifflin-St Jeor vs Harris-Benedict

The Harris-Benedict formula dates from 1919 and is still common. In the 1990 study, it overestimated measured resting energy by 5% on average. In the 2013 study, it was one of the formulas that tended to guess too high, while Mifflin-St Jeor did not. So for most adults, Mifflin-St Jeor is the better choice.

Mifflin-St Jeor vs Katch-McArdle and other lean-mass formulas

Some formulas use your lean mass instead: your weight minus your body fat. In 1980, a researcher called Cunningham looked again at the 1919 data from 223 people. Lean mass alone predicted BMR well, and sex and age added little. His formula is 500 + 22 × lean mass in kg. Whether metabolism really slows with age is in does metabolism slow with age.

The Katch-McArdle formula, which many apps use, also starts from lean mass. This post uses Cunningham’s, because we could check it in its original journal paper.

Lean-mass formulas need a good body-fat number. If your body-fat figure is off, the answer moves with it. For our example woman, Cunningham’s formula gives 1,622 kcal at 25% body fat but 1,472 kcal at 35% (our calculation). That is a 150 kcal swing from the body-fat number alone.

Activity factors for Mifflin-St Jeor

Your BMR is only the energy you burn at rest. To estimate all the calories you burn in a day, your TDEE or maintenance calories, you multiply your BMR by an activity factor. Experts call it your physical activity level, or PAL.

The standard ranges come from a 2004 expert report. Three bodies wrote it together: the Food and Agriculture Organization (FAO), the World Health Organization (WHO) and the United Nations University (UNU). It is advice written by a panel of experts after reviewing the research.

The report says levels above 2.40 are hard to keep up for long. One hour a day of jogging, cycling or sport can lift a desk worker from about 1.55 to 1.75. In a review of 411 adults with mostly desk-based Western lifestyles, a typical level was about 1.60.

So choosing your activity level matters more than choosing a BMR formula. If you can’t decide between two levels, try the lower one for a few weeks and see what your weight does.

What about Indian adults?

India’s National Institute of Nutrition (ICMR-NIN) looked at this in 2020. It compared the FAO/WHO/UNU formulas with BMR measured in Indian adults. The formulas can overestimate Indian BMR by 10–12%, because their data included many young, muscular people. Indians tend to carry relatively more body fat.

So ICMR-NIN now takes about 10% off the FAO/WHO/UNU result for Indian adults, in two cuts of 5%. It also lowered the activity factor for sedentary people from 1.53 to 1.40, because Indian studies found that daily tasks used less energy.

This change was made for the FAO/WHO/UNU formulas, not for Mifflin-St Jeor. No study in our library has tested Mifflin-St Jeor in Indian adults. If you are of Indian origin, your real needs may be a little lower than any formula suggests. Your weight trend over a few weeks will show you.

Claims and evidence

• ClaimA BMR calculator tells you exactly how many calories you burn.

  EvidenceIt gives an estimate. Mifflin-St Jeor landed within 10% for 82% of adults tested, so about 1 in 5 people were further off than that.

• ClaimHarris-Benedict and Mifflin-St Jeor are equally good.

  EvidenceIn the 1990 study, Harris-Benedict overestimated measured resting energy by 5%. Reviews in 2005 and 2013 ranked Mifflin-St Jeor first of the common formulas.

• ClaimA lean-mass formula is always more accurate.

  EvidenceLean mass predicts BMR well, but only if your body-fat number is right. For our example woman, a 10-point change in body fat moved Cunningham’s answer by 150 kcal a day.

• ClaimVery active people should multiply their BMR by 2.5 or more.

  EvidenceThe FAO/WHO/UNU report says activity levels above 2.40 are hard to keep up for long. Levels that high are seen in extreme cases, such as three weeks of bike racing.

What this means for you

What the research can’t tell you yet

• Your own number. Every formula gives an average for people like you. Only a lab test of your breathing at rest measures your BMR directly.
• Who was studied. The formula and its main tests come from US adults. They included too few older adults and people from ethnic minorities, and we found no test in Indian adults.
• Newer data. The main review is from 2005, and the 2013 study tested one group of 337 adults.
• Real life. Activity factors describe a whole lifestyle. They can’t follow a week that is busier or quieter than usual.

How Bodyvault uses this research

Bodyvault starts your calorie target with the Mifflin-St Jeor formula. If you add a body-fat reading, it switches to a lean-mass formula (Katch-McArdle), and the targets screen shows which one it used. With Bodyvault Pro, the adaptive mode then blends that first guess with what your weigh-ins and logged food show over four weeks. That way, your target follows your real body rather than the formula.

General information about fitness and nutrition, not medical advice. If you have a health condition, are pregnant or take medication, talk to your doctor before changing your diet or training.