Your Basal Metabolic Rate (BMR) is the number of calories your body burns in 24 hours at complete rest. That energy keeps your heart beating, lungs breathing, brain working and body temperature steady. For most people, BMR accounts for 60–70% of all the calories they burn in a day. This calculator estimates BMR with the Mifflin-St Jeor equation, which the Academy of Nutrition and Dietetics considers the most accurate predictive formula for healthy adults. It then multiplies BMR by an activity factor to estimate your total daily needs (TDEE).
How to use the BMR calculator
- Select your sex. Men and women have different average body composition, so the formula differs.
- Enter your age, height in cm and weight in kg. If you need to convert, our Length and Weight converters can help.
- Choose your activity level honestly. Most office workers who exercise a few times a week are “lightly” or “moderately” active.
- Press Calculate BMR to see your BMR, maintenance calories and the targets for gentle weight loss or gain.
The Mifflin-St Jeor equation
Women: BMR = 10 × weight (kg) + 6.25 × height (cm) − 5 × age (y) − 161
Worked examples
- Man, 30, 175 cm, 75 kg: 750 + 1,093.75 − 150 + 5 = 1,699 kcal/day. Moderately active (× 1.55), his TDEE is about 2,633 kcal.
- Woman, 28, 160 cm, 58 kg: 580 + 1,000 − 140 − 161 = 1,279 kcal/day. Lightly active (× 1.375), her TDEE is about 1,759 kcal.
From BMR to daily calories (TDEE)
Total Daily Energy Expenditure (TDEE) adds everything else you do to your BMR: walking, working, exercising and digesting food. It is estimated by multiplying BMR by an activity factor:
| Activity level | Description | Multiplier |
|---|---|---|
| Sedentary | Desk job, little or no exercise | 1.2 |
| Lightly active | Light exercise 1–3 days a week, or a job with some walking | 1.375 |
| Moderately active | Moderate exercise 3–5 days a week | 1.55 |
| Very active | Hard exercise 6–7 days a week | 1.725 |
| Extra active | Physical labour plus training, or athletes training twice a day | 1.9 |
People tend to overestimate their activity. If you are unsure, pick the lower level, track your weight for 2–3 weeks and adjust.
Other BMR formulas
| Formula | Year | Notes |
|---|---|---|
| Harris-Benedict (revised) | 1984 | Older standard. Tends to overestimate by about 5% in modern populations. Gives about 1,763 kcal for the man above. |
| Mifflin-St Jeor | 1990 | Most accurate for the general population. Used here. |
| Katch-McArdle | Not dated | Uses lean body mass (needs your body-fat %). Better for very lean or very muscular people. |
What affects your BMR?
- Muscle mass: muscle burns more energy at rest than fat. Strength training is the most reliable way to raise BMR over time.
- Body size: larger and taller bodies have higher BMRs.
- Age: BMR falls gradually from early adulthood, mainly because of muscle loss. The formula subtracts 5 kcal for each year of age.
- Sex: men usually have more lean mass and higher BMRs.
- Hormones: thyroid disorders can noticeably raise or lower metabolism. If you have unexplained weight change, ask your doctor about a thyroid test.
- Crash dieting: very low intake causes adaptive thermogenesis, where the body burns less than predicted. This is one reason extreme diets stall.
Using BMR for weight goals
To lose weight, eat a little below your TDEE, not below your BMR. About 500 kcal below TDEE gives roughly 0.5 kg loss a week. Eating below BMR for long periods makes it harder to get enough protein and micronutrients, and is hard to sustain. For a full daily target with protein, carbs and fat, use the Calorie Calculator.
Reference: Mifflin MD, St Jeor ST et al., “A new predictive equation for resting energy expenditure in healthy individuals”, American Journal of Clinical Nutrition, 1990. These are estimates; individuals can differ by ±10% or more.
Frequently asked questions
What is a normal BMR?
It depends on size, age and sex. Many adult women fall between about 1,200 and 1,500 kcal a day, and many adult men between about 1,500 and 1,900 kcal. A larger or more muscular body has a higher BMR.
What is the difference between BMR and TDEE?
BMR is what you burn at complete rest. TDEE is your total daily burn including movement and exercise, estimated as BMR × an activity factor from 1.2 to 1.9.
Which BMR formula is the most accurate?
For most healthy adults, Mifflin-St Jeor is considered the most accurate predictive equation. If you know your body-fat percentage and are very lean or muscular, Katch-McArdle can be better.
Should I eat less than my BMR to lose weight?
Generally, no. Aim for a moderate deficit below your TDEE, typically 300–500 kcal a day. Eating below BMR for long periods can lead to muscle loss, nutrient shortfalls and a slower metabolism.
How can I increase my BMR?
Build muscle with regular strength training, eat enough protein, stay active through the day, sleep well and avoid crash diets. Muscle is metabolically more active than fat.