BMR Calculator — Basal Metabolic Rate
Find your Basal Metabolic Rate — the calories your body burns just to keep you alive at complete rest. Compare four published formulas, see your hourly resting burn, and how your BMR is likely to change with age.
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How Your BMR Changes With Age
Mifflin-St Jeor at your current weight and height — the formula lowers BMR by 5 kcal a day for each year of age.
| Age | BMR | Per Hour | vs Today |
|---|
How this calculator works
This uses the Mifflin-St Jeor equation, a widely used general-population predictive equation. No BMR equation is universally most accurate for every person.
Men: 10W + 6.25H − 5A + 5 · Women: 10W + 6.25H − 5A − 161 — W = weight in kg · H = height in cm · A = age in years
For comparison it also shows the revised Harris-Benedict equation (Roza & Shizgal, 1984) and, if you enter your body-fat percentage, the lean-mass-based Katch-McArdle (370 + 21.6 × LBM) and Cunningham (500 + 22 × LBM) equations.
By Suhaib Hassan · Reviewed 28 September 2026 against the original published equations · How CalculatePilot verifies formulas →
BMR vs. total daily energy expenditure
BMR is just your resting energy use — it doesn't include activity. Multiply BMR by an activity factor (roughly 1.2 to 1.9) to estimate your total daily calorie needs, which is what the range above shows as rough bounds. For a more precise activity-adjusted number, use our TDEE Calculator.
BMR changes over your lifetime
BMR generally decreases with age, partly due to natural muscle loss over time (since muscle burns more calories at rest than fat tissue) — this is one reason calorie needs often decrease gradually as people get older even without weight changes.
Maintaining muscle mass through resistance training may help preserve resting energy expenditure as body composition changes with age, although individual changes vary.
A worked example
A 28-year-old woman, 65kg, 165cm: BMR works out to 10 times 65 plus 6.25 times 165 minus 5 times 28 minus 161, which equals 650 plus 1,031 minus 140 minus 161, or 1,380 calories/day at complete rest.
At a sedentary activity level (times 1.2), her estimated daily calorie needs would be about 1,656; at a very active level (times 1.725), that rises to roughly 2,381 — a difference of over 700 calories purely from activity level.
Factors that influence your BMR beyond this formula
While the Mifflin-St Jeor equation is widely used for general-purpose estimation, individual resting energy expenditure can vary due to genetics, muscle mass, hormone levels (including thyroid function), and even body temperature regulation — meaning your actual BMR could differ somewhat from the formula's estimate. Medical information, not medical advice.
Sources
- Mifflin et al. (1990), A new predictive equation for resting energy expenditure — PubMed
- Roza AM, Shizgal HM. The Harris Benedict equation reevaluated. Am J Clin Nutr 1984;40:168–182.
- Cunningham JJ. A reanalysis of the factors influencing basal metabolic rate in normal adults. Am J Clin Nutr 1980;33:2372–2374.
- Mayo Clinic Calorie Calculator
How to calculate BMR by hand
Example: a 35-year-old man, 80 kg, 180 cm, with the Mifflin-St Jeor equation.
- 10 × 80 = 800
- 6.25 × 180 = 1,125
- 5 × 35 = 175
- 800 + 1,125 − 175 + 5 = 1,755 kcal a day
Multiplying by 1.2 (sedentary) gives about 2,106 kcal and by 1.55 (moderately active) about 2,720 kcal.
Mifflin-St Jeor vs revised Harris-Benedict
The revised Harris-Benedict equation (Roza and Shizgal, 1984) is: men 88.362 + 13.397W + 4.799H − 5.677A; women 447.593 + 9.247W + 3.098H − 4.330A (W in kg, H in cm, A in years). Results at age 30, men 178 cm and women 165 cm:
| Weight | Man: Mifflin | Man: Harris-Benedict | Woman: Mifflin | Woman: Harris-Benedict |
|---|---|---|---|---|
| 55 kg | 1,518 | 1,509 | 1,270 | 1,337 |
| 65 kg | 1,618 | 1,643 | 1,370 | 1,430 |
| 75 kg | 1,718 | 1,777 | 1,470 | 1,522 |
| 85 kg | 1,818 | 1,911 | 1,570 | 1,615 |
| 95 kg | 1,918 | 2,045 | 1,670 | 1,707 |
The two formulas can differ by 100 kcal or more, which is why the calculator shows several. Your own measured BMR can differ from any of them.
Muscle, fat and your BMR
Published estimates put the resting energy use of skeletal muscle at roughly 13 kcal per kg a day and of fat at roughly 4.5 kcal per kg a day (Wang et al., 2010). That means adding 5 kg of muscle raises resting burn by only about 65 kcal a day, a modest effect that is still worth having.
BMR vs RMR
BMR is measured under strict resting conditions. Resting metabolic rate (RMR) is measured under looser conditions and is the figure most formulas, including these, actually estimate. In everyday use the two terms are often treated as the same.
Read the guides: BMR vs TDEE: what is the difference? · How to calculate your TDEE
Frequently asked questions
What's the difference between BMR and calorie needs?
BMR is the energy used at complete rest. Your actual daily calorie needs (TDEE) are higher because they include movement, exercise, and digestion.
Which BMR formula is most accurate?
Mifflin-St Jeor is widely used and performs well in validation studies, but no predictive BMR equation is universally most accurate for every person.
Is the Mifflin-St Jeor formula the most accurate?
It is a widely used general-population equation, but any formula is an estimate and individual energy needs can differ meaningfully from the prediction.
Can I increase my BMR?
Increasing or preserving lean mass can affect resting energy expenditure, but the size of the change varies between people; strength training is useful for maintaining muscle and overall fitness, not a guarantee of a specific BMR increase.
How much does BMR typically decline with age?
BMR tends to decline gradually with age, partly due to natural muscle loss over time — maintaining muscle mass through strength training can help offset this decline.
How do I calculate my BMR by hand?
Use Mifflin-St Jeor: 10 x weight (kg) + 6.25 x height (cm) - 5 x age, then add 5 for men or subtract 161 for women. An 80 kg, 180 cm, 35-year-old man gets 1,755 kcal a day.
What is the difference between BMR and RMR?
BMR is measured under strict resting conditions, RMR under less strict ones. Prediction formulas are really estimating resting energy use, so the terms are often used interchangeably.
Why does Harris-Benedict give a different answer?
It uses different coefficients from a different population. For a 28-year-old woman, 65 kg and 165 cm, Mifflin-St Jeor gives 1,380 kcal and revised Harris-Benedict about 1,439 kcal.
What is a normal BMR?
It depends on sex, age, height and weight. For a 30-year-old man of 178 cm, Mifflin-St Jeor gives about 1,518 to 1,918 kcal for weights from 55 to 95 kg.
How much does muscle raise BMR?
Only modestly. Using roughly 13 kcal per kg a day for muscle, 5 kg of extra muscle adds about 65 kcal a day.
Next Steps
Add activity and goals to your resting burn.