What is basal metabolic rate (BMR)?
Your BMR is the energy your body burns just to stay alive while resting: breathing, pumping blood, keeping organs working, regulating temperature and repairing cells. For most people it is the biggest share of daily calorie use, with the rest going to movement and to digesting food. This calculator estimates it from your age, sex, height and weight, and shows what that means for your daily calorie needs.
BMR is measured under strict lab conditions, so online tools like this one give an estimate. Use the number as a starting point, then adjust using real-world results over a few weeks.
What affects your BMR?
- Muscle mass: muscle burns more at rest than fat, so more lean mass means a higher BMR.
- Age: BMR tends to decline gradually with age, partly through loss of muscle.
- Size and sex: larger bodies burn more, and men on average burn more than women of the same weight.
- Genetics and health: thyroid function, hormones and illness all play a part.
- Diet history: long, severe calorie restriction can lower metabolic rate.
- Temperature: very cold or hot environments increase energy use.
BMR is not the same as resting metabolic rate (RMR), which is measured under looser conditions, or TDEE, which adds activity. The numbers are usually close enough that the terms are often used interchangeably.
BMR calculator FAQ
What is BMR?
BMR (basal metabolic rate) is the energy your body needs at complete rest to keep vital functions running, such as breathing, circulation and cell repair. It is usually the largest part of the calories you burn in a day.
Which BMR formula is the most accurate?
The Mifflin-St Jeor equation is widely regarded as the most reliable for most people. Katch-McArdle can be better for lean people who know their body fat percentage, because it uses lean body mass. All formulas are estimates.
What is the difference between BMR and TDEE?
BMR is what you burn at rest. TDEE (total daily energy expenditure) adds the calories used for movement, exercise and digesting food. It is estimated by multiplying BMR by an activity factor, as shown in the activity table.
Can I eat less than my BMR to lose weight?
Eating far below your BMR for long periods is not recommended, because it can cause fatigue, muscle loss and nutrient shortfalls. A moderate deficit below your daily needs is the usual approach. Talk to a doctor or dietitian before using very low targets.
Does building muscle raise my BMR?
Yes, slightly. Muscle burns more energy at rest than fat, so more lean mass raises BMR over time. Strength training is the most effective way to build it.
Important
This calculator gives general estimates for adults and is not medical advice. If you are pregnant, under 18, managing a health condition or planning significant changes to your diet, talk to a doctor or registered dietitian. Last updated October 2026.