A BMR calculator estimates your basal metabolic rate: the calories your body burns at complete rest to keep you alive. This tool uses the Mifflin-St Jeor equation. A 35-year-old man who weighs 80 kg and is 180 cm tall has an estimated BMR of 1,755 kcal a day.
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How to use the BMR calculator
- Choose your sex.
- Enter your age, weight and height.
- Read your estimated BMR in kcal per day.
- Multiply by an activity factor, or use the TDEE calculator, to estimate total daily calories.
BMR formula (Mifflin-St Jeor)
- Men: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) + 5
- Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (years) − 161
To convert, kg = lb × 0.45359237 and cm = inches × 2.54. The result is in kilocalories (kcal) per day; multiply by 4.184 for kilojoules.
BMR calculator worked example
Man, 35 years, 80 kg, 180 cm:
| Step | Value |
|---|---|
| 10 × 80 | 800 |
| 6.25 × 180 | 1,125 |
| −5 × 35 | −175 |
| Sex constant | +5 |
| BMR | 1,755 kcal/day |
A woman of 35 years, 65 kg and 165 cm: 650 + 1,031.25 − 175 − 161 ≈ 1,345 kcal/day, or about 5,629 kJ.
Which BMR equation is most accurate?
| Equation | Man above | Woman above | Notes |
|---|---|---|---|
| Mifflin-St Jeor (1990) | 1,755 | 1,345 | Used by this BMR calculator |
| Revised Harris-Benedict (1984) | 1,825 | 1,408 | Tends to give higher results |
| Katch-McArdle | Needs body fat % | Needs body fat % | 370 + 21.6 × lean mass (kg) |
A systematic review in the Journal of the American Dietetic Association (Frankenfield and colleagues, 2005) found that Mifflin-St Jeor was the equation most often within 10% of measured resting metabolic rate in both non-obese and obese adults. Even so, some individuals were more than 10% off, with errors largest in the very obese and in older adults. Only a lab measurement such as indirect calorimetry gives your true value.
BMR vs RMR vs TDEE
- BMR: energy used at complete rest after fasting, measured under strict lab conditions.
- RMR (resting metabolic rate): measured under less strict conditions; usually slightly higher than BMR. The two terms are often used interchangeably, and the Mifflin-St Jeor equations were derived from resting measurements.
- TDEE (total daily energy expenditure): BMR plus the energy used to digest food plus all activity. This is your maintenance calorie level; use the TDEE calculator to estimate it.
What affects BMR?
- Body size and composition: more lean mass means a higher BMR.
- Age: BMR tends to fall with age, partly because of muscle loss. In the formula, each extra year lowers the estimate by 5 kcal.
- Sex: men usually have a higher BMR at the same weight and height because of greater lean mass; the formula constants differ by 166 kcal.
- Other factors: thyroid function, some medications, illness, pregnancy and very low calorie intake.
Strength training that adds muscle can raise BMR modestly. Large, quick changes are not realistic.
How to use your BMR result
A BMR calculator result is a starting point, not a diet target. Most adults burn more than their BMR every day, so eating at or below it for long periods is not usually advised without medical supervision. To plan weight change, estimate total daily needs first, then adjust intake gradually and track your weight over several weeks; your real trend is a better guide than any equation. The NIH Body Weight Planner models how intake and activity change weight over time. Pregnant or breastfeeding people, children and anyone with a medical condition should get advice from a clinician or registered dietitian.
For education only, not medical advice.
BMR in kilojoules
Food labels in Australia, New Zealand and much of Europe show energy in kilojoules. To convert a BMR calculator result, multiply the BMR calculator’s kcal figure by 4.184. A BMR of 1,700 kcal a day is about 7,113 kJ a day. Use the BMR calculator result in the same unit as the labels you read.
Related converters and calculators
Related tools:
- TDEE calculator: maintenance calories
- Calorie calculator: daily needs
- Macro calculator: protein, carbs, fat
- BMI calculator: weight for height
- Body fat calculator: lean mass for Katch-McArdle
Sources
Mifflin MD et al. A new predictive equation for resting energy expenditure in healthy individuals. Am J Clin Nutr, 1990; Frankenfield D et al. Comparison of predictive equations for resting metabolic rate. J Am Diet Assoc, 2005; NIH NIDDK: Body Weight Planner.
Questions about this calculator
What is a normal BMR?
It depends on size, age and sex. For the examples above, Mifflin-St Jeor gives about 1,755 kcal for an 80 kg man and 1,345 kcal for a 65 kg woman.
Which BMR formula is most accurate?
In a 2005 systematic review, Mifflin-St Jeor was most often within 10% of measured values in adults.
Is BMR the same as calories I should eat?
No. Daily needs (TDEE) are higher because they include digestion and activity.
Does BMR go down with age?
Usually, partly because lean mass falls. The formula subtracts 5 kcal per year of age.
How can I measure BMR exactly?
Through indirect calorimetry in a clinic or lab.
Check the assumptions and units before relying on a result. Financial, tax and health estimates do not replace advice for your individual circumstances.
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