Your basal metabolic rate (BMR) is the energy your body uses at complete rest to keep you alive — breathing, circulation, temperature. For most adults the Mifflin–St Jeor equation estimates it best: 10 × weight (kg) + 6.25 × height (cm) − 5 × age, then +5 for men or −161 for women. Multiply BMR by an activity factor to get your TDEE.
Key takeaways
- BMR is typically 60–70% of the calories you burn in a day; the rest is activity and digesting food.
- Mifflin–St Jeor predicts resting energy within ±10% for more people than any other common equation.
- If you know your body fat, Katch–McArdle and Cunningham use lean mass and can be more accurate for very lean or muscular people.
- Never plan to eat below your BMR for long without medical supervision.
How this BMR calculator works
Enter your sex, age, weight and height and the calculator applies three height-and-weight equations at once. Add a body-fat percentage and it adds the two lean-mass equations. It then multiplies the Mifflin–St Jeor result by the five standard activity factors so you can see your total daily energy expenditure (TDEE) straight away.
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BMR is close to, but not the same as, resting metabolic rate, and the RMR calculator explains how the two differ. If you are over 50, see the BMR calculator for women over 50.
The BMR formulas
Mifflin–St Jeor (1990) is the default because it predicts measured resting energy most reliably in healthy adults (Mifflin et al., 1990; Frankenfield et al., 2005):
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5 Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
Harris–Benedict is the oldest equation, published in 1918 and revised in 1984 (Harris & Benedict, 1918; Roza & Shizgal, 1984). It is still widely used but tends to run a little high for modern populations.
Katch–McArdle and Cunningham ignore age and sex and use lean body mass instead (McArdle, Katch & Katch; Cunningham, 1980):
Katch–McArdle: BMR = 370 + 21.6 × lean mass(kg) Cunningham: BMR = 500 + 22 × lean mass(kg) lean mass = weight × (1 − body fat % ÷ 100)
Worked example
For a 35-year-old woman who is 165 cm (5′5″) tall and weighs 74.8 kg (165 lb):
| Step | Calculation | Result |
|---|---|---|
| Weight term | 10 × 74.8 | 748 |
| Height term | 6.25 × 165.1 | 1,032 |
| Age term | 5 × 35 | −175 |
| Sex constant | women | −161 |
| BMR | 748 + 1,032 − 175 − 161 | ≈ 1,444 kcal/day |
At a moderate activity level (× 1.55) her TDEE is about 2,239 kcal/day. That is the number to plan around, not the BMR.
BMR by age and sex
These are Mifflin–St Jeor BMRs for an average-height US adult (women 5′4″/163 cm at 170 lb/77 kg; men 5′9″/175 cm at 200 lb/91 kg). Use them to sanity-check your own result.
| Age | Women (kcal/day) | Men (kcal/day) |
|---|---|---|
| 20 | 1,528 | 1,909 |
| 30 | 1,478 | 1,859 |
| 40 | 1,428 | 1,809 |
| 50 | 1,378 | 1,759 |
| 60 | 1,328 | 1,709 |
| 70 | 1,278 | 1,659 |
How accurate is a BMR calculator?
Prediction equations estimate the average for people like you. In a review of prediction equations, Mifflin–St Jeor landed within 10% of measured resting energy for roughly 8 in 10 non-obese adults and 7 in 10 adults with obesity (Frankenfield et al., 2005). If your weight trend doesn’t match what your calculated numbers predict after 2–4 weeks, trust the scale. That is exactly what an adaptive TDEE calculator does.
What changes your BMR
- Lean mass. Muscle and organs drive most resting energy, which is why the lean-mass equations work.
- Body size. Bigger bodies need more energy, so BMR falls as you lose weight.
- Age. Resting energy declines slowly in later adulthood, which is why the equation subtracts 5 kcal per year.
- Dieting. After sustained weight loss, measured expenditure can fall below the level predicted from body size, and how much varies between people (Rosenbaum & Leibel, 2010).
Frequently asked questions
What is a normal BMR?
For most adult women BMR falls between about 1,200 and 1,500 kcal/day, and for men between about 1,500 and 1,900 kcal/day. It scales mainly with body size and lean mass, so taller, heavier and more muscular people have higher BMRs, and BMR drifts down slowly with age.
Is BMR the same as RMR?
Nearly. BMR is measured under strict conditions (after sleep, fasted, fully rested), while resting metabolic rate (RMR) is measured under looser ones and runs a few percent higher. Mifflin–St Jeor was actually derived from RMR measurements, and in everyday use the two terms are interchangeable. See TDEE vs BMR vs RMR.
Should I eat my BMR to lose weight?
No. Your BMR is what you burn lying still all day; your real expenditure (TDEE) is higher. Set a fat-loss target as a 10–20% reduction from TDEE instead, which for most people stays well above BMR. Use the calorie deficit calculator to set it.
Which BMR formula is the most accurate?
In a systematic review of predictive equations, Mifflin–St Jeor came closest to measured resting energy in the most people, both with and without obesity. Harris–Benedict tends to overestimate by a few percent. Lean-mass formulas (Katch–McArdle, Cunningham) are only as good as your body-fat estimate.
Why does BMR go down when I lose weight?
A smaller body needs less energy to maintain, so every equation predicts a lower BMR as weight falls. Measured resting energy can drop further than predicted — a process called adaptive thermogenesis — which is one reason weight loss slows over time.
References
- Mifflin MD, St Jeor ST, Hill LA, Scott BJ, Daugherty SA, Koh YO (1990). A new predictive equation for resting energy expenditure in healthy individuals. American Journal of Clinical Nutrition 51(2):241–247.
- Harris JA, Benedict FG (1918). A biometric study of human basal metabolism. Proceedings of the National Academy of Sciences 4(12):370–373.
- Roza AM, Shizgal HM (1984). The Harris Benedict equation reevaluated: resting energy requirements and the body cell mass. American Journal of Clinical Nutrition 40(1):168–182.
- McArdle WD, Katch FI, Katch VL (2015). Exercise Physiology: Nutrition, Energy, and Human Performance (8th ed.). Wolters Kluwer Health.
- Cunningham JJ (1980). A reanalysis of the factors influencing basal metabolic rate in normal adults. American Journal of Clinical Nutrition 33(11):2372–2374.
- Frankenfield D, Roth-Yousey L, Compher C (2005). Comparison of predictive equations for resting metabolic rate in healthy nonobese and obese adults: a systematic review. Journal of the American Dietetic Association 105(5):775–789.
- Rosenbaum M, Leibel RL (2010). Adaptive thermogenesis in humans. International Journal of Obesity 34(Suppl 1):S47–S55.