🔥 BMR Calculator: Find Your Basal Metabolic Rate
By Shihab Mia · Reviewed by ToolNimba Editorial Review, health content · Updated 2026-06-26
This calculator gives an estimate for healthy adults and is not medical advice. BMR varies with body composition, genetics, hormones and health conditions. Speak to a doctor or registered dietitian before making decisions about your calorie intake.
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest just to keep you alive: breathing, circulating blood, and running your organs. This calculator uses the Mifflin-St Jeor equation, the formula most dietitians prefer today. Enter your sex, age, height and weight in metric or imperial units to get your BMR in kcal/day, plus an estimate of your total daily calorie needs at five activity levels.
What is the BMR Calculator?
BMR is the largest single piece of your daily energy budget, usually 60% to 70% of the calories you burn. It covers only the involuntary work of staying alive, measured in a rested, fasted state at a comfortable temperature. Everything else you do, from walking to the fridge to running a marathon, sits on top of that baseline. A closely related term, Resting Metabolic Rate (RMR), is measured under slightly less strict conditions and runs a few percent higher, but in everyday use the two numbers are treated as interchangeable.
Several formulas estimate BMR from simple measurements. The Mifflin-St Jeor equation, published in 1990, replaced the older Harris-Benedict equation in most clinical settings because studies found it more accurate for modern populations, landing within about 10% of measured values for most healthy adults. It uses weight in kilograms, height in centimetres, age in years, and a constant that differs by sex: men add 5, women subtract 161. The result reflects that, at the same height and weight, men typically carry more lean muscle, which burns more energy at rest than fat.
The original Harris-Benedict equation dates to 1919 and tends to overestimate BMR by roughly 5% to 15% for today's more sedentary, heavier population, which is why dietitians moved away from it. A third option, the Katch-McArdle formula, ignores age and sex entirely and instead works from lean body mass, so it needs your body fat percentage as an input. Because it uses lean mass directly, Katch-McArdle is often the most accurate choice for lean, muscular, or very athletic people whose body composition is unusual for their height and weight. For most people who do not know their body fat percentage, Mifflin-St Jeor is the sensible default, and that is the equation this calculator uses.
To turn BMR into a usable daily target you multiply it by an activity factor to get your Total Daily Energy Expenditure (TDEE), the calories you actually burn in a day. TDEE is the sum of four parts: BMR, the thermic effect of food (the energy spent digesting meals, around 10%), exercise activity, and non-exercise activity thermogenesis (NEAT) such as fidgeting, standing and walking around. Eating around your TDEE keeps weight stable, eating below it tends to cause weight loss, and eating above it tends to cause gain.
These numbers are estimates, not measurements. Real metabolism is shaped by muscle mass, genetics, sleep, stress, thyroid and other hormones, body temperature and even the climate you live in. Prediction equations can be off by a few hundred calories in either direction for any one person. The honest way to use your result is as a starting point: pick a calorie target based on it, track your weight and intake for two to four weeks, and then nudge the number up or down based on what actually happens on the scale.
Finally, BMR naturally drifts down with age, dropping a few percent each decade as adults tend to lose muscle and gain fat. The single most reliable lever you have to keep your resting burn higher is preserving and building muscle through strength training and adequate protein, because muscle is metabolically more active than fat. That is why two people of the same weight can have noticeably different BMRs.
When to use it
- Finding a sensible daily calorie target before planning a cut, bulk or maintenance diet.
- Understanding how much of your energy use is the fixed baseline versus activity you can change.
- Setting a safe weight-loss deficit or weight-gain surplus around your maintenance calories.
- Comparing how age, weight or muscle gain shift your resting calorie burn over time.
- Checking whether a crash diet is dropping you below your BMR, which is rarely advisable.
- Giving a personal trainer or dietitian a baseline number to refine your nutrition plan.
How to use the BMR Calculator
- Choose metric (cm/kg) or imperial (ft-in/lb) units.
- Select your sex, since the formula uses a different constant for men and women.
- Enter your age, height and current weight.
- Read your BMR in kcal/day, the calories you burn at complete rest.
- Look at the activity table for your estimated daily calorie needs (TDEE), then subtract about 500 for weight loss or add about 300 to 500 for lean gain.
Formula & method
Worked examples
A 30-year-old man, 80 kg, 180 cm tall.
- BMR = 10 × 80 + 6.25 × 180 − 5 × 30 + 5
- = 800 + 1125 − 150 + 5
- = 1780 kcal/day
Result: BMR 1,780 kcal/day (sedentary TDEE ~2,136 kcal/day)
A 30-year-old woman, 65 kg, 165 cm tall.
- BMR = 10 × 65 + 6.25 × 165 − 5 × 30 − 161
- = 650 + 1031.25 − 150 − 161
- = 1370 kcal/day (rounded)
Result: BMR 1,370 kcal/day (sedentary TDEE ~1,644 kcal/day)
Same woman, but moderately active and aiming to lose weight. Take her BMR of 1,370 and apply the moderate activity factor, then subtract a 500 kcal deficit.
- TDEE = 1370 × 1.55 = 2124 kcal/day (maintenance)
- Weight-loss target = 2124 − 500
- = 1624 kcal/day
Result: Maintenance ~2,124 kcal/day; weight-loss target ~1,624 kcal/day for about 0.5 kg (1 lb) loss per week
Activity multipliers to turn BMR into TDEE (daily calorie needs)
| Activity level | Description | Multiply BMR by |
|---|---|---|
| Sedentary | Little or no exercise, desk job | 1.2 |
| Lightly active | Light exercise 1 to 3 days/week | 1.375 |
| Moderately active | Moderate exercise 3 to 5 days/week | 1.55 |
| Very active | Hard exercise 6 to 7 days/week | 1.725 |
| Extra active | Very hard exercise or a physical job | 1.9 |
The three main BMR formulas and when to use each
| Formula | Year | Inputs used | Best for |
|---|---|---|---|
| Mifflin-St Jeor | 1990 | Weight, height, age, sex | The default for most people; most accurate general equation |
| Harris-Benedict (revised) | 1984 | Weight, height, age, sex | Older standard, tends to overestimate slightly |
| Katch-McArdle | 1996 | Lean body mass (needs body fat %) | Lean or very athletic people who know their body fat |
Typical BMR ranges by sex and age (Mifflin-St Jeor, average height and weight)
| Group | Age range | Approximate BMR (kcal/day) |
|---|---|---|
| Adult women | 20 to 39 | 1,300 to 1,500 |
| Adult women | 40 to 59 | 1,200 to 1,400 |
| Adult men | 20 to 39 | 1,600 to 1,900 |
| Adult men | 40 to 59 | 1,500 to 1,800 |
Common mistakes to avoid
- Confusing BMR with daily calorie needs. BMR is your rest-only baseline. The calories you can eat in a day is your TDEE, which is BMR multiplied by an activity factor. Eating only your BMR is usually too low.
- Mixing units. Entering height in cm but weight in pounds (or the reverse) produces a wildly wrong number. Pick metric or imperial and keep both inputs in the same system.
- Overstating your activity level. Most people who sit for work and train a few times a week are lightly to moderately active, not very active. Choosing too high a factor inflates your target and stalls weight loss.
- Treating the estimate as exact. A prediction equation can be off by a few hundred calories for any one person. Use the number as a starting point and adjust based on two to four weeks of real-world results.
- Eating below your BMR for long stretches. Dropping intake under your basal needs to lose faster can backfire, costing you muscle and energy. Aim for a moderate deficit from TDEE rather than crashing below BMR.
- Ignoring muscle and body composition. Two people of the same weight can have different BMRs because muscle burns more at rest than fat. If you are very lean or muscular, the Katch-McArdle formula may fit you better.
Glossary
- BMR
- Basal Metabolic Rate: the calories your body burns at complete rest to sustain basic functions.
- RMR
- Resting Metabolic Rate: a close cousin of BMR measured under less strict conditions, usually a few percent higher.
- TDEE
- Total Daily Energy Expenditure: BMR plus the energy used for activity and digestion, your true daily calorie burn.
- Mifflin-St Jeor equation
- A 1990 formula that estimates BMR from weight, height, age and sex, widely used by dietitians.
- Harris-Benedict equation
- An older BMR formula from 1919 (revised 1984) that tends to overestimate slightly for modern adults.
- Katch-McArdle formula
- A BMR formula based on lean body mass, useful when you know your body fat percentage.
- Activity factor
- A multiplier (1.2 to 1.9) applied to BMR to account for how active you are.
- NEAT
- Non-Exercise Activity Thermogenesis: calories burned through everyday movement like fidgeting, standing and walking, outside of planned exercise.
Frequently asked questions
What is BMR?
BMR (Basal Metabolic Rate) is the number of calories your body burns at complete rest to keep essential functions like breathing, circulation and cell repair running. It is typically 60% to 70% of your total daily calorie use.
How do I calculate my BMR?
Enter your sex, age, height and weight above and the tool applies the Mifflin-St Jeor equation. By hand: men use 10 × kg + 6.25 × cm − 5 × age + 5, and women use the same first part but subtract 161 instead of adding 5. The answer is in calories per day.
What is the Mifflin-St Jeor equation?
It is a formula that estimates BMR from weight in kg, height in cm, age and sex. Men: 10 × kg + 6.25 × cm − 5 × age + 5. Women use the same first part but subtract 161. It is considered more accurate than the older Harris-Benedict equation for most healthy adults.
How is BMR different from TDEE?
BMR is your resting calorie burn only. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor, so it reflects everything you do in a day, including exercise and digestion. TDEE is the number to use for setting a daily calorie target.
Which BMR formula is the most accurate?
For the general population, Mifflin-St Jeor is the most accurate prediction equation and lands within about 10% of measured values for most people. If you are very lean or muscular and know your body fat percentage, the Katch-McArdle formula, which uses lean body mass, can be more accurate for you.
Why is BMR different for men and women?
On average, at the same height and weight men carry more lean muscle, which burns more energy at rest than fat. The Mifflin-St Jeor formula captures this by adding 5 for men and subtracting 161 for women.
How many calories should I eat to lose weight?
Find your TDEE (your maintenance calories) and eat below it. A deficit of about 500 calories a day from TDEE is a common, sustainable target for roughly 0.5 kg (about 1 lb) of loss per week. Avoid eating below your BMR for long periods.
Can I eat below my BMR to lose weight faster?
It is generally not recommended. Eating below your basal needs for an extended time can cost you muscle, lower your energy and make the diet hard to sustain. A moderate deficit from your TDEE, rather than dropping under your BMR, is safer and more effective.
Does BMR decrease with age?
Yes. BMR tends to fall a few percent each decade in adulthood, largely because people lose muscle and gain fat over time. Strength training and eating enough protein help preserve muscle and keep your resting calorie burn higher.
Does this calculator store my data?
No. The calculation runs entirely in your browser using JavaScript. Nothing you enter is sent to a server or saved anywhere.
Sources
- A new predictive equation for resting energy expenditure in healthy individuals , American Journal of Clinical Nutrition (Mifflin et al.) (1990)
- Basal Metabolic Rate (BMR): What It Is and How To Calculate It , Cleveland Clinic
- Dietary Guidelines for Americans, Estimated Calorie Needs , U.S. Department of Health and Human Services