BMR Calculator
Estimate your Basal Metabolic Rate — the calories your body burns at complete rest — using the Mifflin-St Jeor equation. BMR is the foundation for setting calorie targets for weight loss, maintenance, or gain.
How to Use
- Select your sex — the Mifflin-St Jeor equation uses a different constant for men and women.
- Enter your age in years.
- Enter your weight in kilograms and height in centimeters.
- Read your BMR in calories per day — the energy you would burn lying still for 24 hours.
- To find your full daily calorie need, multiply BMR by an activity factor (use the TDEE Calculator for this step).
Show Work
Formulas
About the BMR Calculator
The BMR Calculator is a free tool for health and fitness tracking. It runs right in your web browser, so there is nothing to download. Estimate your Basal Metabolic Rate — the calories your body burns at complete rest — using the Mifflin-St Jeor equation. BMR is the foundation for setting calorie targets for weight loss, maintenance, or gain.
How it works
Type your numbers into the boxes. The answer shows up right away — you do not have to press a button. If you change a number, the answer changes too. So you can try different numbers and watch what happens, or check an answer you worked out yourself. Just make sure each box has the right kind of number in it.
Want the deeper story? The Knowledge Base explains the ideas behind the tools in more detail.
Frequently Asked Questions
What is the difference between BMR and TDEE?
BMR is the energy your body uses at complete rest to keep organs functioning — breathing, circulation, cell production. TDEE (Total Daily Energy Expenditure) is your full daily burn including digestion, daily movement, and exercise. TDEE is calculated by multiplying BMR by an activity factor (1.2 for sedentary up to about 1.9 for athletes), and it is the number you actually eat to.
Why does this calculator use Mifflin-St Jeor?
The Mifflin-St Jeor equation (1990) is the most accurate BMR estimate for the general modern population according to multiple validation studies. The older Harris-Benedict equation tends to overestimate by around 5%. If you know your body-fat percentage, the Katch-McArdle formula can be slightly more precise because it is based on lean mass, but for most people Mifflin-St Jeor is the right default.
How accurate is an estimated BMR?
Prediction equations are typically within about 10% of measured BMR for most people, but individual metabolism varies with genetics, muscle mass, hormones, and medical conditions. The only precise measurement is indirect calorimetry in a lab. Treat the number as a well-informed starting point and adjust based on how your weight responds over a few weeks.
Does BMR decrease with age?
Yes. The equation subtracts roughly 5 calories per year of age, reflecting the gradual decline in metabolic rate as we get older — largely driven by loss of muscle mass. Strength training and maintaining lean mass are the most effective ways to keep BMR higher as you age.
Should I eat at my BMR to lose weight?
No — eating only your BMR (and then moving around all day) usually creates an aggressive deficit that is hard to sustain and risks nutrient shortfalls. Calculate your TDEE first, then subtract a moderate 300–500 calories. This tool is informational and not a substitute for advice from a clinician or registered dietitian.
How do I use the BMR Calculator?
Just type your numbers. The answer shows up right away — there is no button to press. Change anything and it updates by itself.
Is it free? Does it work without internet?
Yes to both. It is free with no sign-up, and once the page has loaded it keeps working even with no internet.
Where does my data go?
Nowhere — every calculation runs on your own device. Nothing you enter is uploaded, logged, or stored.
Common Use Cases
Setting a calorie baseline
Establish your resting calorie burn before layering on activity to plan a diet.
Tracking metabolic change
Recalculate after significant weight change to see how your resting burn shifts.
Comparing equations
See how Mifflin-St Jeor and Harris-Benedict differ for your own numbers.
Planning a deficit or surplus
Use BMR as the input to a TDEE calculation for fat loss or lean-bulk targets.
Understanding age-related metabolism
See how your estimated resting burn changes across the decades.
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