Understanding This Calculator
Basal Metabolic Rate is the number of calories your body needs to maintain vital functions — breathing, circulation, cell production — while completely at rest. It typically accounts for 60-75% of total daily calorie burn, making it the foundation for any calorie or weight-management plan.
This calculator uses the Mifflin-St Jeor equation, published in 1990 and validated as more accurate than the older Harris-Benedict formula across most modern populations.
- w weight in kilograms
- h height in centimeters
- a age in years
| Formula | Year | Notes |
|---|---|---|
| Mifflin-St Jeor | 1990 | Most accurate for modern populations (used here) |
| Harris-Benedict | 1919 (rev. 1984) | Older, tends to overestimate by 5% |
| Katch-McArdle | — | Uses lean body mass; needs body-fat % input |
Frequently Asked Questions
Is BMR the same as the calories I should eat?
No — BMR is calories at complete rest. Your Total Daily Energy Expenditure (TDEE), which factors in activity, is what you should use for calorie targets. See our TDEE Calculator.
Why does BMR decrease with age?
Muscle mass naturally declines with age, and muscle is metabolically more active than fat, so BMR tends to drop roughly 1-2% per decade after age 20.
What is the Basal Metabolic Rate Calculator?
The Basal Metabolic Rate (BMR) Calculator is a precise physiological assessment tool used to determine the exact number of calories your body needs to accomplish its most basic life-sustaining functions. BMR accounts for roughly 60 to 75 percent of your daily calorie expenditure. These life-sustaining functions include breathing, blood circulation, cellular growth, brain function, and body temperature regulation. Understanding your BMR is essential for anyone serious about managing their diet and weight.
By inputting simple metrics such as age, gender, height, and weight, the calculator strips away the variables of exercise and daily movement to reveal your absolute baseline caloric need. This figure serves as the critical starting point for nutritional planning. For instance, if you want to lose weight in a healthy manner, you must ensure you consume enough calories to meet your BMR, creating a caloric deficit primarily through physical activity rather than extreme starvation diets that can harm your metabolism.
How to Calculate Basal Metabolic Rate (The Formula)
The BMR Calculator typically utilizes either the Harris-Benedict equation or the more modern Mifflin-St Jeor equation, the latter being considered more accurate. The Mifflin-St Jeor equation calculates BMR as follows. For Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) + 5. For Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age in years) - 161. These formulas are rooted in the relationship between body mass, surface area, and energy expenditure.
Frequently Asked Questions
What is the difference between BMR and RMR (Resting Metabolic Rate)?
While often used interchangeably, BMR and RMR are slightly different. BMR measures your absolute minimum energy needs under highly strict laboratory conditions (typically after fasting and a full night's sleep). RMR, or Resting Metabolic Rate, measures calories burned at rest but under less strict conditions, meaning RMR estimates are usually slightly higher than BMR.
Is it safe to eat fewer calories than my BMR?
It is generally not recommended to consistently consume fewer calories than your BMR. Eating below this baseline can signal your body that it is starving, causing it to slow down metabolic functions, break down muscle mass for energy, and negatively impact hormone levels and immune function.
Does my BMR change if I lose weight?
Yes, as you lose weight, your BMR will decrease. A smaller body mass requires less energy to sustain its basic functions. This is why weight loss often plateaus; you must continuously recalculate your BMR and adjust your caloric intake or activity levels to continue losing weight.