Estimates only, not medical advice. These are population formulas, and any one person can be well above or below them. If you are pregnant or breastfeeding, under 18, have diabetes, kidney disease, an eating disorder or another medical condition, or take medicine that affects weight, talk to your doctor or a registered dietitian before changing how you eat.
How BMR is estimated
Nobody can measure BMR from a tape measure and a scale, so calculators use equations fitted to people whose resting energy was measured in a lab. This one shows three of them. They all give calories per day.
Mifflin-St Jeor (1990): 10W + 6.25H − 5A + 5 for men, − 161 for women
Harris-Benedict, revised by Roza and Shizgal (1984): men 88.362 + 13.397W + 4.799H − 5.677A; women 447.593 + 9.247W + 3.098H − 4.330A
Katch-McArdle: 370 + 21.6 × lean body mass
W = weight in kg, H = height in cm, A = age in years, lean body mass = W × (1 − body fat %)
- Mifflin and colleagues measured 498 healthy adults and found the 1919 Harris-Benedict equations ran about 5% high. A 2005 systematic review later found Mifflin-St Jeor the most likely of the common equations to fall within 10% of measured resting energy, so it is the headline number here.
- Roza and Shizgal re-fitted the Harris-Benedict equations in 1984 on 337 measurements. Their version is the one most calculators use today.
- Katch-McArdle swaps age and sex for lean body mass, because muscle burns more at rest than fat. It needs a body fat percentage, and it is only as good as that number. It is a textbook formula from exercise physiology, and we could not find one original study behind it.
Worked example: a 45-year-old woman, 5 ft 4 in, 150 lb, 30% body fat
150 lb is 68.04 kg and 5 ft 4 in is 162.56 cm.
- Mifflin-St Jeor: 10 × 68.04 + 6.25 × 162.56 − 5 × 45 − 161 = 680.4 + 1,016.0 − 225 − 161 = 1,310 calories.
- Harris-Benedict: 447.593 + 9.247 × 68.04 + 3.098 × 162.56 − 4.330 × 45 = 447.6 + 629.2 + 503.6 − 194.9 = 1,386 calories.
- Katch-McArdle: lean mass is 68.04 × 0.70 = 47.63 kg, so 370 + 21.6 × 47.63 = 1,399 calories.
That is about 55 calories an hour, even asleep. Ten years on at the same weight, Mifflin-St Jeor would put her at 1,260. This example is loaded when the page opens.
What BMR is useful for
BMR on its own is a starting block. Multiply it by your activity level to get the calories you burn in a day with the TDEE calculator, then set a goal with the calorie calculator. Comparing the three formulas also shows how uncertain any single estimate is: if they differ by 100 calories, do not read much into the last digit.
Limits
- Individual error is large. The 2005 review found that even the best equation misses by more than 10% for a sizeable minority of people.
- The studies behind these equations under-represented older adults and US ethnic minorities, according to the same review.
- Illness, fever, thyroid conditions, some medicines, pregnancy and breastfeeding all change resting energy. The formulas do not account for them.
- For adults 18 and over only.
Sources checked October 2026.
Questions people ask
What is BMR?
Basal metabolic rate is the energy your body uses in a day at complete rest: breathing, circulating blood, keeping warm and running your organs. It is usually the largest part of the calories you burn, and it does not include digesting food, walking about or exercise. Strictly, BMR is measured after an overnight fast lying still; the formulas here estimate resting energy expenditure, which is very close.
What is a normal BMR?
There is no single normal figure, because BMR depends mostly on body size, and also on sex and age. For the example on this page, a 45-year-old woman at 5 ft 4 in and 150 lb, the three formulas give about 1,310 to 1,400 calories a day. A taller or heavier person will have a higher BMR.
Is BMR the same as TDEE?
No. TDEE (total daily energy expenditure) is BMR multiplied by an activity factor of about 1.2 to 1.9. BMR is the floor of what you burn lying still; TDEE is what you burn on a normal day. Use the TDEE calculator for the second number.
Should I eat my BMR to lose weight?
Not as a rule. BMR is what you burn at rest, so eating only that much on an active day is a bigger cut than it looks. A safer approach is to start from your TDEE and take off about 500 calories a day. We don’t show targets under 1,200 calories a day for women or 1,500 for men, the low ends of the 2013 AHA/ACC/TOS ranges. That floor is our conservative choice; the guideline itself reserves diets under 800 calories a day for medically supervised programs.
Does BMR go down with age?
In the Mifflin-St Jeor equation, every extra year takes 5 calories a day off the estimate, or 50 calories a decade, if your weight stays the same. Part of the real-life drop comes from losing muscle, which is why strength training is often recommended as people get older.
How can I measure my BMR exactly?
Only with indirect calorimetry, a test that measures the oxygen you breathe in and the carbon dioxide you breathe out. Some hospitals, universities and clinics offer it. Every online BMR calculator, including this one, gives an estimate.