Free BMR Calculator
Estimate the calories your body burns at rest each day with the Mifflin-St Jeor and Harris-Benedict formulas.
Enter your age, sex, weight and height. The calculator applies the Mifflin-St Jeor equation and the revised Harris-Benedict equation to estimate the energy your body uses at complete rest, in kilocalories and kilojoules per day.
How to use the BMR Calculator
- Choose metric or US units and enter your own measurements.
- Read the result and the supporting numbers shown beneath it.
- Use the explanation below to see what the number means, and talk to a doctor about anything that worries you.
About the BMR Calculator
Estimate the calories your body burns at rest each day with the Mifflin-St Jeor and Harris-Benedict formulas.
Health numbers are easier to understand when you can see how they are worked out. These calculators use published formulas and explain what the result does and does not tell you. They give general estimates and are not medical advice.
What is basal metabolic rate?
Your basal metabolic rate (BMR) is the energy your body uses to stay alive while doing nothing: keeping your heart beating, your lungs working, your body warm and your cells repairing themselves. It is measured after resting in a warm room, usually in the morning after fasting.
For most people BMR makes up the largest part of daily energy use. The rest comes from movement, exercise and digesting food.
The two formulas used here
The calculator shows two widely used equations, with weight in kilograms, height in centimetres and age in years.
- Mifflin-St Jeor (1990): men 10 × weight + 6.25 × height − 5 × age + 5. Women 10 × weight + 6.25 × height − 5 × age − 161.
- Revised Harris-Benedict (1984): men 88.362 + 13.397 × weight + 4.799 × height − 5.677 × age. Women 447.593 + 9.247 × weight + 3.098 × height − 4.330 × age.
- Worked example: a 30-year-old man who is 175 cm and 70 kg. Mifflin-St Jeor gives 700 + 1,093.75 − 150 + 5 = 1,649 kcal a day. Harris-Benedict gives 1,696 kcal a day, a gap of 47.
What changes your BMR
Several things move your resting energy use up or down, which is why no formula is exact.
- Body size and composition. More lean mass raises BMR, and larger bodies burn more.
- Age. BMR tends to fall as muscle mass declines over the years.
- Sex. Men on average have more lean mass, which is why the formulas differ.
- Hormones, illness, pregnancy and some medicines can raise or lower it.
- Temperature and very low calorie intake can both change it.
BMR, RMR and TDEE
You will see three similar terms. BMR is the strict resting figure. Resting metabolic rate (RMR) is measured under looser conditions and is usually a little higher. Total daily energy expenditure (TDEE) adds the energy of movement, exercise and eating, and is the number that matters for weight management.
To go from BMR to TDEE, multiply by an activity factor. The calorie calculator on this site does this and shows targets for losing or gaining weight.
Limits of the estimate
These equations were built from studies of adults and are intended for ages 15 and up in this calculator. They do not suit pregnancy, breastfeeding, serious illness or people with very high or very low body fat. If you need an exact figure for medical reasons, a clinic can measure it with indirect calorimetry.
Getting started with the BMR Calculator
Using the bmr calculator takes a minute or two. Your entries are saved in this browser, so you can come back later and carry on.
Tips for better results
BMR is not the number of calories you should eat. Most people burn well above it because of daily movement, so use the calorie calculator to turn BMR into a maintenance figure.
Use measurements you have taken recently, not remembered ones.
These tools give general estimates and are not medical advice. Check anything important with a doctor or registered dietitian.
Privacy and where your data goes
Everything you type into the bmr calculator stays on your own device. Zapxa does not receive your numbers or documents. If you clear your browser data, your saved entries will be removed, so download a PDF of anything you want to keep.
Frequently asked questions
What is BMR?
Basal metabolic rate is the energy your body needs each day to keep you alive at rest: breathing, circulation, temperature control and cell repair. It usually accounts for the largest share of the calories you burn.
Which formula is more accurate, Mifflin-St Jeor or Harris-Benedict?
Mifflin-St Jeor, published in 1990, is generally preferred for modern populations. The revised Harris-Benedict equation dates from 1984 and often gives a slightly higher figure. Both are estimates, and the gap between them is shown above.
Should I eat my BMR in calories?
No. BMR is the energy for resting alone. Your maintenance calories are higher once daily activity is included, and the calorie calculator does that step for you.
Why is my measured BMR different from the estimate?
Formulas use averages. Muscle mass, genetics, hormones, medicines and illness all change the real figure, so a measured result from a clinic can differ by a few hundred calories.
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