For most people, Mifflin-St Jeor is the best default BMR formula. Use Katch-McArdle only if you know your body fat percentage reasonably well, and treat Harris-Benedict as a useful cross-check that runs slightly higher. The three formulas usually land within about 100 to 200 calories of each other, which is small compared with the error in guessing your activity level.
For an 80 kg, 180 cm, 30-year-old man with 20% body fat: Mifflin-St Jeor gives 1,780 calories, revised Harris-Benedict gives 1,854, and Katch-McArdle gives 1,752. Choose a formula in the calorie calculator and compare them yourself.
📑 Table of Contents
What BMR is and how it differs from RMR and TDEE
- BMR (basal metabolic rate): the energy your body uses at complete rest to keep you alive: breathing, circulation, temperature and cell repair.
- RMR (resting metabolic rate): very close to BMR and measured under easier conditions. The formulas on this page are technically estimates of resting energy, but people call them BMR.
- TDEE (total daily energy expenditure): BMR plus the calories from movement, exercise and digesting food. This is the number you eat around to maintain, lose or gain weight.
Typically BMR is about 60 to 70 percent of a sedentary person's TDEE, so a small error in BMR carries through to your daily target.
The three formulas
Use weight (W) in kilograms, height (H) in centimeters and age (A) in years. To convert, divide pounds by 2.2046 and multiply inches by 2.54.
| Formula | Men | Women | Needs body fat? |
|---|---|---|---|
| Mifflin-St Jeor (1990) | 10W + 6.25H − 5A + 5 | 10W + 6.25H − 5A − 161 | No |
| Harris-Benedict, revised (1984) | 88.362 + 13.397W + 4.799H − 5.677A | 447.593 + 9.247W + 3.098H − 4.330A | No |
| Katch-McArdle | 370 + 21.6 × lean body mass (kg) | Yes | |
For Katch-McArdle, lean body mass = weight × (1 − body fat percentage). A person weighing 80 kg at 20% body fat has 64 kg of lean mass. The original 1919 Harris-Benedict equation also exists, but the 1984 revision is the version most tools use.
Same people, three results
Here are three example people run through every formula, with the spread between the highest and lowest result:
| Person | Mifflin-St Jeor | Harris-Benedict (rev.) | Katch-McArdle | Spread |
|---|---|---|---|---|
| Man, 30, 80 kg, 180 cm, 20% fat | 1,780 | 1,854 | 1,752 | 102 |
| Woman, 35, 65 kg, 165 cm, 28% fat | 1,345 | 1,408 | 1,381 | 63 |
| Man, 40, 100 kg, 178 cm, 32% fat | 1,918 | 2,055 | 1,839 | 216 |
| Woman, 25, 55 kg, 160 cm, 22% fat | 1,264 | 1,344 | 1,297 | 80 |
Two patterns show up. Revised Harris-Benedict is the highest in all four cases, by about 60 to 140 calories above Mifflin-St Jeor. And Katch-McArdle moves with body composition: for the man with 32 percent body fat it comes out 79 calories below Mifflin-St Jeor, because he carries less lean mass for his weight.
Worked calculation: the 80 kg man
- Mifflin-St Jeor: 10 × 80 + 6.25 × 180 − 5 × 30 + 5 = 800 + 1,125 − 150 + 5 = 1,780
- Harris-Benedict: 88.362 + 13.397 × 80 + 4.799 × 180 − 5.677 × 30 = 88.362 + 1,071.76 + 863.82 − 170.31 = 1,854
- Katch-McArdle: 370 + 21.6 × 64 = 370 + 1,382.4 = 1,752
Which formula is most accurate
A widely cited 2005 review by the Academy of Nutrition and Dietetics compared several equations against measured resting metabolic rate and found Mifflin-St Jeor was most often within 10 percent of the measured value for both non-obese and obese adults. That is why it is the usual default in modern calculators.
No formula is exact. Two people with the same height, weight, age and sex can differ by several hundred calories in real life because of muscle mass, genetics, thyroid function, medications, sleep and other factors. These equations give an average for people like you, not a measurement of you.
How to choose
| Your situation | Best choice | Why |
|---|---|---|
| You just want a reliable starting number | Mifflin-St Jeor | Best validated, needs only basic details. |
| You know your body fat from a DEXA scan or a trusted measurement | Katch-McArdle | Uses lean mass, so it suits muscular or very lean people. |
| You guess your body fat from a mirror or a scale | Mifflin-St Jeor | A wrong body fat figure makes Katch-McArdle less reliable than the simpler formulas. |
| You want a second opinion | Harris-Benedict (revised) | Treat it as the higher end of a likely range. |
You can estimate body fat with the body fat calculator, which is useful for Katch-McArdle, though estimates from a tape measure are rougher than a scan.
From BMR to daily calories
Multiply BMR by an activity factor to estimate TDEE:
| Activity level | Factor | 80 kg man (Mifflin BMR 1,780) |
|---|---|---|
| Little or no exercise | 1.2 | 2,136 |
| Light exercise, 1 to 3 days a week | 1.375 | 2,448 |
| Moderate exercise, 3 to 5 days a week | 1.55 | 2,759 |
| Hard exercise, 6 to 7 days a week | 1.725 | 3,071 |
| Very hard exercise or a physical job | 1.9 | 3,382 |
Notice that the activity level moves the answer by about 1,250 calories, far more than the 100 to 200 calories between formulas. If you are unsure, pick the lower of two levels. The step-by-step method is in the daily calorie needs guide, and the deficit math is in the calorie deficit guide.
How to check your number in real life
- Calculate maintenance calories with one formula and an honest activity level.
- Eat about that amount for 2 to 3 weeks and weigh yourself under the same conditions, ideally each morning.
- If your weekly average weight is stable, your estimate is close.
- If it drifts up or down, shift calories by 100 to 200 and try again. Your own results beat any formula.
How to use the calculator
Enter your details
Add age, sex, height, weight and activity level.
Pick a formula
Choose Mifflin-St Jeor, Harris-Benedict or Katch-McArdle (add body fat for the last one).
Compare the results
Switch formulas to see the range, then start from the middle and adjust by your results.
Compare BMR formulas side by side
BMR, TDEE and macros, free and no signup.
Open the Calorie CalculatorFrequently Asked Questions
Conclusion
Start with Mifflin-St Jeor, cross-check with Harris-Benedict, and switch to Katch-McArdle only if you have a trustworthy body fat figure. The gap between them is modest, so spend your effort on an honest activity level and on tracking your weight trend. Try all three in the calorie calculator.
This guide gives estimates from standard equations and is not medical or dietary advice. Consult a doctor or registered dietitian for personal nutrition needs.