What is BMR?
Your Basal Metabolic Rate (BMR) is the number of calories your body needs to stay alive at complete rest — powering your heart, lungs, brain and kidneys and the constant work of repairing and replacing cells. If you spent an entire day lying still, you would still burn roughly this many calories. For most people BMR is the single largest part of daily energy use, accounting for around 60–70% of the calories burned each day.
BMR is driven mainly by your size and composition: taller, heavier people and those with more muscle burn more at rest, while BMR tends to fall with age as muscle mass declines. Sex matters too — men usually have a higher BMR than women of the same height and weight because they tend to carry more lean tissue.
How BMR is calculated
This calculator uses the Mifflin-St Jeor equation, published in 1990 and widely regarded as the most accurate predictive formula for healthy adults. In metric units:
Men: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women: BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161
The only difference between the sexes is the final constant, which reflects the average difference in lean body mass. You can switch to Harris-Benedict or Katch-McArdle in the calculator to compare.
Worked example
Generated by the same engine that powers the calculator above, for a 30-year-old man, 175 cm and 75 kg, using Mifflin-St Jeor.
| Step | Value |
|---|---|
| 10 × weight (75 kg) | 750 |
| + 6.25 × height (175 cm) | 1,093.75 |
| − 5 × age (30) | −150 |
| + 5 (male constant) | +5 |
| BMR (Mifflin-St Jeor) | 1,699 kcal/day |
| TDEE if moderately active (× 1.55) | 2,633 kcal/day |
From BMR to TDEE: activity multipliers
BMR only covers rest. To estimate the calories you actually burn — your Total Daily Energy Expenditure (TDEE) — multiply BMR by an activity factor. Pick the row that best matches a typical week.
| Activity level | Factor | Typical week |
|---|---|---|
| Sedentary | 1.2 | Little or no exercise, desk job |
| Light Exercise | 1.375 | Light exercise 1–3 days/week |
| Moderate Exercise | 1.55 | Moderate exercise 3–5 days/week |
| Active | 1.725 | Hard exercise 6–7 days/week |
| Very Active | 1.9 | Twice-daily training or a physical job |
| Elite Athlete | 2.1 | Professional-level training load |
Typical BMR by age and sex
For a rough sense of scale, here is how BMR changes with age at an average build.
| Age | Men (175 cm, 75 kg) | Women (162 cm, 62 kg) |
|---|---|---|
| 20 | 1,749 kcal | 1,372 kcal |
| 30 | 1,699 kcal | 1,322 kcal |
| 40 | 1,649 kcal | 1,272 kcal |
| 50 | 1,599 kcal | 1,222 kcal |
| 60 | 1,549 kcal | 1,172 kcal |
Indicative figures at an average build, generated by the calculator’s engine. Your own BMR depends on your exact height, weight and body composition.
Which formula should you use?
This calculator offers three respected BMR equations. They usually agree within a few percent, but each has a sweet spot.
| Formula | Equation | Best for |
|---|---|---|
| Mifflin-St Jeor | 10W + 6.25H − 5A + s | Most people — the modern default, validated as the most accurate general estimate. |
| Harris-Benedict (revised) | 13.397W + 4.799H − 5.677A + 88.362 (men) | Comparison with older research and tools; tends to read slightly higher. |
| Katch-McArdle | 370 + 21.6 × lean body mass | Lean, muscular individuals who know their body-fat percentage. |
Limitations
BMR formulas are population estimates, not personal measurements. They are validated for adults, not children, and become less accurate at the extremes of body composition — very muscular or very high body-fat individuals may be better served by the Katch-McArdle formula or a lab measurement by indirect calorimetry. Expect any predictive equation to be within about 10% of your true resting metabolic rate. Use this figure as a starting point and adjust based on real-world results, and consult a qualified professional before making significant dietary changes.
Frequently asked questions
What is BMR (basal metabolic rate)?+
BMR is the number of calories your body burns at complete rest to keep vital functions like breathing, circulation and cell production running. It is the largest part of your daily calorie burn, usually 60–70% of the total.
How is BMR calculated?+
This calculator uses the Mifflin-St Jeor equation: for men, BMR = 10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5; for women the final term is −161. You can also switch to the Harris-Benedict or Katch-McArdle formulas.
What is the difference between BMR and TDEE?+
BMR is calories burned at rest. TDEE (Total Daily Energy Expenditure) multiplies BMR by an activity factor to include daily movement and exercise, so it is the calories you actually burn in a day. The activity table above shows your TDEE at every activity level.
Which BMR formula is most accurate?+
Mifflin-St Jeor is considered the most accurate predictive equation for most healthy adults. Harris-Benedict is the older standard and tends to read slightly higher, while Katch-McArdle is best when you know your body-fat percentage because it works from lean mass.
Why do men and women have different BMR?+
On average men carry more lean muscle mass, which burns more energy at rest, so the male equation has a higher constant (+5 versus −161 for women).
Does BMR decrease with age?+
Yes. BMR generally declines with age as lean muscle mass falls, which is why the equation subtracts 5 calories for each year of age.
Should I eat below my BMR to lose weight?+
No. Eating below your BMR is not recommended. Create a moderate deficit from your TDEE instead — typically around 500 calories a day — ideally with professional guidance.
How accurate is this BMR calculator?+
Predictive equations estimate BMR within roughly 10% of a laboratory measurement by indirect calorimetry. Treat the figure as a well-grounded starting point rather than an exact number.
Is BMR the same as resting metabolic rate (RMR)?+
They are very close. RMR (or REE) is measured under slightly less strict conditions and can be up to about 10% higher than true BMR; in everyday use the terms are often interchangeable.
How can I increase my BMR?+
Building lean muscle through resistance training raises resting energy expenditure. Staying active and eating enough protein also help support your metabolic rate over time.
Sources
- Mifflin MD, St Jeor ST, et al. “A new predictive equation for resting energy expenditure in healthy individuals.” Am J Clin Nutr, 1990;51(2):241–247.
- StatPearls / NCBI Bookshelf — Basal Metabolic Rate (definition and context).
- Roza AM, Shizgal HM — revised Harris-Benedict equations (comparison formula).
Formula and sources last reviewed by the TheCalculatorVault team on 26 June 2026. BMR figures are estimates for general information, not medical advice.
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