BMR Calculator
Calculate your basal metabolic rate (BMR) and daily calorie needs (TDEE) from age, sex, height and weight using the Mifflin-St Jeor or Harris-Benedict formula.
Choose this if you do moderate exercise 3-5 days a week.
The modern, most widely used BMR formula — with higher accuracy.
What Is Basal Metabolic Rate (BMR)?
This basal metabolic rate calculator (also useful as a metabolism calculator) finds the minimum number of calories your body burns over 24 hours at complete rest — with no physical activity — to keep its basic functions running. These functions include breathing, heartbeat, maintaining body temperature, hormone production and cell repair. In short, metabolism is the whole set of processes by which your body uses and converts energy; BMR represents its most basic, at-rest layer.
Your basal metabolic rate makes up 60–75% of total daily energy expenditure (TDEE). That is why BMR is the starting point for any plan to lose or gain weight: TDEE = BMR × Activity Factor.
How to Calculate BMR — The Formulas
Two formulas stand out in the scientific literature for calculating BMR, so this tool works as both a Mifflin-St Jeor calculator and a Harris-Benedict calculator:
- Mifflin-St Jeor (1990) — Recommended: Men: BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5 | Women: subtract 161 from the same formula. Modern research shows this formula is 80–90% accurate for the general population.
- Harris-Benedict (1984 revision): Men: 88.362 + (13.397 × kg) + (4.799 × cm) − (5.677 × age) | Women: 447.593 + (9.247 × kg) + (3.098 × cm) − (4.330 × age). A classic formula that can slightly overestimate in active, muscular people.
- Katch-McArdle (lean-mass based): Not included in this tool, but it gives a more accurate result for athletes who know their body-fat percentage and have high muscle mass.
Example: for a 30-year-old, 175 cm, 75 kg man using Mifflin-St Jeor: (10 × 75) + (6.25 × 175) − (5 × 30) + 5 = 750 + 1,093.75 − 150 + 5 = 1,699 kcal/day.
How to Speed Up Your Metabolism
Scientifically supported methods for boosting metabolism include:
- Build muscle: Muscle tissue burns about 3 times more calories at rest than fat. Regular resistance training meaningfully raises BMR over time.
- HIIT and aerobic exercise: High-intensity interval training keeps metabolism elevated for 24–48 hours after exercise (the EPOC effect).
- Eat enough protein: Protein has a thermic effect of 25–30%, requiring far more energy to digest than carbs or fat. A high-protein diet can raise metabolism by 80–100 kcal/day.
- Get enough quality sleep: Sleep deprivation raises cortisol and ghrelin, which can slow metabolism by 10–15% and increase appetite.
- Stay hydrated: Drinking 500 ml of cold water can raise metabolism by 10–30% for about 30 minutes; aim for 2–2.5 liters of water a day.
- Don't skip meals: Prolonged calorie restriction can push the body into "conservation mode" and lower BMR; regular, adequate eating keeps metabolism active.
TDEE: Activity Factor and Daily Calorie Needs
Used as a TDEE calculator and daily calorie needs calculator, the tool answers how many calories do I burn a day: after finding your basal metabolic rate, multiply it by the factor for your activity level below to estimate your total daily energy expenditure (TDEE). Your TDEE is also your maintenance calorie level — the intake that keeps your weight stable:
| Activity Level | Factor | Description |
|---|---|---|
| Sedentary | × 1.2 | Desk job, no exercise |
| Lightly Active | × 1.375 | Light exercise 1–3 days/week |
| Moderately Active | × 1.55 | Moderate exercise 3–5 days/week |
| Active | × 1.725 | Hard exercise 6–7 days/week |
| Very Active | × 1.9 | 2 workouts/day or physical job |
How Metabolism Changes With Age and Sex
Metabolic rate is not fixed; it changes with age, sex, body composition and hormonal status, among other factors. Because men generally have more muscle mass than women, their basal metabolic rate is on average 5–10% higher. With aging, metabolism drops by about 2–3% per decade, which is why someone eating the same calories may gain weight more easily at 40 than at 25.
Metabolism rises noticeably during pregnancy and breastfeeding. Hypothyroidism (an underactive thyroid) can significantly slow it down; if you have unexplained weight gain, thyroid testing is advisable.
TDEE and Calorie Balance — BMR in Practice
Once you have your basal metabolic rate, just multiply by the activity factor to get your total daily calorie needs (TDEE). As a maintenance calorie calculator, that TDEE figure is the number of calories that keeps your weight steady. The general scientific guideline is to eat 300–500 kcal below your TDEE to lose weight, or 250–500 kcal above it to gain. A daily deficit or surplus of 500 kcal gives about 0.5 kg of change per week. One kilogram of fat corresponds to roughly 7,700 kcal.
Results from any BMR calculator are estimates. The most accurate way to measure your real metabolic rate is indirect calorimetry at rest, but that test is done in a clinical setting. This tool uses the Mifflin-St Jeor formula by default, which gives the most accurate result for most people.
How to Use This BMR Calculator
To use the BMR calculator, enter your sex, age, height and weight, then choose your activity level. The tool gives you both your BMR (resting calorie needs) and your TDEE (total daily calorie needs). You can use these values to:
- Track calories: Compare your TDEE with your daily intake to understand your real calorie balance.
- Manage weight: Set daily calorie targets based on your goal (lose, maintain or gain).
- Plan exercise: Change the activity factor to see how your calorie needs shift as you train harder.
- Track progress: Your BMR changes as you lose weight or your muscle mass changes; update the calculation every 4–6 weeks and adjust your plan.
- Talk to a dietitian: Sharing the calculated values with a dietitian is the most effective way to build a personalized nutrition plan.
Basal metabolic rate varies considerably from person to person. Due to genetics and hormonal factors, the calculated value can differ from your real BMR by ±10–15%. If you have unexplained weight changes or fatigue, consult a health professional. Knowing your TDEE lets you build a science-based rather than guesswork-based weight plan, and helps you get sustainable results in the long run.
Calculating BMR Step by Step
- Select your sex: The BMR formulas differ for men and women, so choosing correctly directly affects the result.
- Enter age, height and weight: Weighing yourself in the morning on an empty stomach and measuring height without shoes gives more accurate results.
- Set your activity level: Choosing a higher level than reality inflates your TDEE; a realistic choice makes weight management easier.
- Choose the formula: Use Mifflin-St Jeor for general use, or Harris-Benedict for classic or very active individuals.
- Interpret the result: BMR is your resting calorie need, while TDEE is your total daily need. Use TDEE as the reference for weight management.
Frequently Asked Questions About the BMR Calculator
Basal metabolic rate (BMR) is the minimum number of calories your body burns over 24 hours at complete rest to keep basic functions like breathing, heartbeat and cell repair running. It makes up 60–75% of total daily energy expenditure (TDEE) and is the starting point for weight management.
Metabolism is the sum of all the chemical processes by which your body converts food into energy and uses that energy. Saying "my metabolism is slow" usually means a low basal metabolic rate — that is, burning few calories at rest.
The most effective methods are: (1) building muscle through resistance training, (2) HIIT exercise, (3) a high-protein diet, (4) getting enough sleep (7–9 hours), and (5) staying well hydrated. Not skipping meals and avoiding extreme calorie restriction also help prevent your metabolism from slowing.
Mifflin-St Jeor: Men BMR = (10 × kg) + (6.25 × cm) − (5 × age) + 5; Women: subtract 161 from the same formula. TDEE = BMR × activity factor (1.2 sedentary — 1.9 very active). Example: for a 30-year-old, 175 cm, 75 kg man, BMR ≈ 1,699 kcal and moderate-activity TDEE ≈ 2,633 kcal.
Current research shows the Mifflin-St Jeor formula is more accurate for the general population. Harris-Benedict is a classic, well-established formula but can slightly overestimate TDEE in active, muscular people. For those who know their body-fat percentage, the Katch-McArdle formula is the most precise.
Eating 500 kcal below your TDEE each day leads to about 0.5 kg of weight loss per week. One kilogram of fat is roughly 7,700 kcal. Going below 1,200 kcal for women or 1,500 kcal for men is not recommended, as it can cause muscle loss and slow your metabolism.
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