About the BMR Calculator
Your basal metabolic rate, or BMR, is the number of calories your body uses each day just to stay alive: breathing, circulating blood, keeping warm and running your organs. This calculator estimates it from your sex, age, weight and height using the Mifflin–St Jeor equation, which most dietitians prefer, and compares it with the revised Harris–Benedict equation. If you know your body fat percentage, it also gives a Katch–McArdle estimate based on lean mass. It works in metric or imperial units and runs entirely in your browser.
Updated October 2026
How to use the BMR Calculator
- 1Choose your sex and whether you want metric or imperial units.
- 2Enter your age, weight and height.
- 3Optionally enter your body fat percentage for a third estimate.
- 4Read your BMR in calories per day in the highlighted box.
- 5Compare the other formulas underneath, then press Copy result.
What the number means
Think of your BMR as the energy cost of being alive. A person who lay in bed all day would still burn about this many calories. Because nobody does that, your real daily burn is higher. The estimate is useful as a starting point for working out maintenance calories, and for understanding why a very large cut in food is hard on the body.
What changes BMR
- Body size: larger bodies burn more energy at rest
- Muscle: lean tissue burns more than fat tissue
- Age: BMR tends to fall gradually in adulthood
- Sex: men usually have a higher BMR at the same weight
- Health and hormones: thyroid problems and some medicines change it
Using the three formulas
Start with Mifflin–St Jeor. If Harris–Benedict is much higher, treat the truth as somewhere between them. Add body fat only if you trust it, for example from a scan; a guess will make the Katch–McArdle result unreliable. Small differences between formulas, usually under 10 percent, are normal and fall well within the natural variation between individuals.
Next steps
Turn BMR into a daily calorie target with the TDEE Calculator or the Calorie Calculator. The Macro Calculator splits calories into protein, carbohydrate and fat, the BMI Calculator checks weight against height, and the Body Fat Calculator estimates the percentage you can type here.
Features
- Mifflin–St Jeor, revised Harris–Benedict and Katch–McArdle formulas
- Metric and imperial units
- Calories per day and per hour
- Optional body fat input
- Clear checks for unrealistic weights, heights and ages
- Nothing leaves your device
Frequently asked questions
What is BMR?
BMR stands for basal metabolic rate. It is the energy your body needs at complete rest, measured in calories per day. For most adults it makes up well over half of the calories burned in a day, with the rest coming from movement and digesting food.
Which BMR formula is the most accurate?
Studies of adults generally find the Mifflin–St Jeor equation to be the closest for most people, which is why it is the main result here. Harris–Benedict tends to run a little higher. Katch–McArdle can be better for very lean or very muscular people, but only if your body fat percentage is accurate.
What is the difference between BMR and TDEE?
BMR is what you burn at rest. Total daily energy expenditure, or TDEE, adds the calories used for daily movement and exercise by multiplying BMR by an activity factor. Use the TDEE Calculator when you want to plan how much to eat.
Can I eat my BMR in calories to lose weight?
Eating at or below your BMR for long periods is not recommended without medical advice, because your body also needs energy for normal activity. A modest deficit from your maintenance calories is the more common approach. This tool gives estimates only and is not medical advice.
Why does my BMR change over time?
BMR falls a little with age, rises with body size and with more muscle, and differs between men and women on average. If your weight or muscle mass changes, recalculate to keep the number current.
Is a BMR estimate reliable for children or pregnant women?
No. These equations were developed for healthy adults. The calculator accepts ages 15 to 100 and warns outside that range. Children, teenagers and pregnant or breastfeeding women have different needs and should follow advice from a health professional.