🔥 BMR Calculator (Basal Metabolic Rate)
By ToolNimba Health Team · Reviewed by ToolNimba Editorial Review, health content · Updated 2026-06-19
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.
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. 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.
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. Eating around your TDEE keeps weight stable, eating below it tends to cause weight loss, and eating above it tends to cause gain. These are estimates: real metabolism is shaped by muscle mass, genetics, sleep, and hormones, so use the number as a starting point and adjust based on how your body responds over a few weeks.
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.
- Comparing how age, weight or muscle gain shift your resting calorie burn over time.
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, then look at the activity table for your estimated daily calorie needs (TDEE).
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)
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 |
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.
Glossary
- BMR
- Basal Metabolic Rate: the calories your body burns at complete rest to sustain basic functions.
- 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.
- Activity factor
- A multiplier (1.2 to 1.9) applied to BMR to account for how active you are.
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.
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.
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. TDEE is the number to use for setting a daily calorie target.
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.
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)
- Dietary Guidelines for Americans, Estimated Calorie Needs , U.S. Department of Health and Human Services