BMR Calculator
What This Tool Does
This calculator estimates your Basal Metabolic Rate — the number of calories your body burns each day just to keep basic functions running while at rest. It also shows your estimated daily calorie needs at different activity levels, giving you a practical starting point for weight loss, maintenance, or muscle gain goals. Enter your age, sex, height, and weight above to get your result.
You can also use this Numerology Calculator.
How It's Calculated
BMR is estimated using one of three established equations. The calculator defaults to the Mifflin-St Jeor Equation, which is currently considered the most accurate for most people.
Mifflin-St Jeor Equation:
- Men: BMR = 10W + 6.25H − 5A + 5
- Women: BMR = 10W + 6.25H − 5A − 161
Revised Harris-Benedict Equation:
- Men: BMR = 13.397W + 4.799H − 5.677A + 88.362
- Women: BMR = 9.247W + 3.098H − 4.330A + 447.593
Katch-McArdle Formula (requires body fat percentage):
- BMR = 370 + 21.6 × (1 − F) × W
Where W = weight in kg, H = height in cm, A = age in years, F = body fat as a decimal.
Worked Example:
Woman, age 30, 165 cm tall, 65 kg:
BMR = (10 × 65) + (6.25 × 165) − (5 × 30) − 161 = 650 + 1,031.25 − 150 − 161 = 1,370 calories/day
This is the minimum her body needs at complete rest. To find daily needs, multiply by an activity factor.
From BMR to Daily Calorie Needs
BMR alone tells you what your body burns at rest. To find your Total Daily Energy Expenditure (TDEE), multiply your BMR by the activity factor that matches your lifestyle:
| Activity Level | Multiplier | Description |
|---|---|---|
| Sedentary | 1.2 | Little or no exercise |
| Lightly active | 1.375 | Exercise 1–3 times/week |
| Moderately active | 1.465 | Exercise 4–5 times/week |
| Very active | 1.55 | Daily exercise or intense training 3–4 times/week |
| Intensely active | 1.725 | Intense exercise 6–7 times/week |
| Extremely active | 1.9 | Very intense daily exercise or physical job |
Using the example above: 1,370 × 1.55 = ~2,124 calories/day to maintain current weight at a very active level.
What Affects Your BMR
Muscle mass: Muscle tissue burns more calories at rest than fat tissue. Strength training builds muscle, which raises BMR over time. Cardio exercise alone does not significantly increase BMR.
Age: BMR tends to decline with age as muscle mass naturally decreases and hormonal changes occur. This is why maintaining resistance training becomes increasingly important as you get older.
Sex: Men generally have higher BMRs than women of the same age and weight due to greater average muscle mass and lower average body fat percentage.
Body composition: Two people of identical weight can have very different BMRs if one has significantly more muscle. The Katch-McArdle formula accounts for this by using lean body mass rather than total weight — making it more accurate for leaner individuals who know their body fat percentage.
Genetics: Hereditary factors influence metabolic rate in ways that are not yet fully understood. Research has shown that even after controlling for all measurable variables, around 26% of BMR variation between individuals remains unexplained.
Temperature: Cold environments raise BMR as the body works to maintain core temperature. Internal body temperature elevation — such as during fever — also increases BMR, by approximately 7% for each rise of 1.36°F in core temperature.
Diet and eating patterns: Eating small, regular meals keeps metabolic rate slightly elevated. Severe caloric restriction or crash dieting can reduce BMR by as much as 30% as the body enters a conservation state — making sustained extreme deficits counterproductive for long-term weight loss.
Pregnancy: BMR increases during pregnancy to support fetal development. Menopause can also shift BMR depending on hormonal changes.
Stimulants: Caffeine and certain supplements raise BMR temporarily. These effects are generally modest and short-lived.
Edge Cases and Special Rules
Formula accuracy varies: The Mifflin-St Jeor Equation is the most accurate for average-weight adults. For leaner individuals who know their body fat percentage, Katch-McArdle tends to be more precise. The Harris-Benedict equation is older and slightly less accurate but still widely referenced.
Age range: These equations are validated for adults aged 15–80. Results for younger children or very elderly individuals may be less reliable.
Estimates only: Even under clinical conditions using specialist equipment, BMR cannot be measured with complete precision. Calculator-based estimates add another layer of approximation on top of that. Use the result as a directional guide, not an exact number.
BMR vs. RMR
These terms are often used interchangeably, but they are technically different. BMR is measured under strict conditions — the person must be completely at rest, in a thermally neutral environment, and in a fasted state after 12 hours without eating. RMR (Resting Metabolic Rate) is measured under more relaxed conditions and is typically 10–20% higher than BMR. Most online calculators, including this one, produce an estimate closer to RMR in practical terms, even when labelled as BMR.
Who Uses This
- People trying to lose weight who need a calorie baseline before setting a deficit target
- Athletes and gym-goers calculating maintenance calories to support training and recovery
- Anyone tracking nutrition who wants to understand how many calories their body actually needs versus how many they consume
- Pregnant women curious about how energy needs shift during pregnancy
- Health-conscious individuals comparing their estimated BMR against their actual food intake
FAQ
How do I use BMR to lose weight?
Start with your TDEE (BMR × activity factor). Create a calorie deficit of 300–500 calories per day below that number. This should produce gradual, sustainable weight loss without triggering significant metabolic slowdown.
Why is my BMR different from what other calculators show?
Different calculators use different equations. Mifflin-St Jeor, Harris-Benedict, and Katch-McArdle produce slightly different results. Small differences in how age, height, and weight are rounded also affect outputs.
Does BMR change if I lose weight?
Yes. As body weight decreases, BMR decreases too — your body needs fewer calories to maintain a smaller mass. Recalculate your BMR after significant weight changes to keep your calorie targets accurate.
Is BMR the same for men and women?
No. At the same weight, age, and height, men typically have a higher BMR due to greater average muscle mass. The equations account for this with different constants for each sex.
Can I increase my BMR?
The most effective way is to build muscle through resistance training, since muscle burns more calories at rest than fat. Adequate sleep, regular eating patterns, and avoiding extreme caloric restriction also help maintain a healthy metabolic rate.
A Note on Results
BMR calculations are estimates based on population-level equations and the inputs you provide. Individual metabolism varies due to genetics, hormones, health conditions, and factors not yet fully understood by science. Use your result as a starting point for planning, track your actual progress over several weeks, and adjust your intake based on real-world results rather than calculator outputs alone. For specific medical or clinical guidance, consult a registered dietitian or healthcare provider.