BMR Calculator
Calculate your Basal Metabolic Rate - the calories your body burns at complete rest. Enter your details to find your BMR using the Mifflin-St Jeor equation.
Your Basal Metabolic Rate (BMR) is the number of calories your body burns at complete rest. This covers basic functions like breathing, circulation, and cell production. It does not include calories burned through movement or exercise.
The Mifflin-St Jeor equation, published in 1990, is considered the most accurate BMR formula for the general population. It replaced the older Harris-Benedict equation from 1919, which tended to overestimate calorie needs.
The Formulas
Men: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) + 5
Women: BMR = (10 × weight in kg) + (6.25 × height in cm) - (5 × age) - 161
To find your total daily calorie needs (TDEE), multiply your BMR by an activity factor. Sedentary folks use 1.2, while highly active people might use 1.725 or even 1.9.
| Age Range | Men (avg BMR) | Women (avg BMR) |
|---|---|---|
| 18-29 years | 1,800 - 2,000 cal/day | 1,400 - 1,600 cal/day |
| 30-49 years | 1,700 - 1,900 cal/day | 1,350 - 1,550 cal/day |
| 50+ years | 1,600 - 1,800 cal/day | 1,300 - 1,500 cal/day |
Values are approximate averages for individuals with normal body composition. Muscle mass, genetics, and health conditions affect individual BMR.
Muscle mass
Muscle burns more calories at rest than fat. A muscular person can have a BMR 100-300 calories higher than someone of the same weight with more body fat.
Age
BMR naturally declines with age, dropping about 1-2% per decade after age 20. This is partly due to muscle loss and hormonal changes.
Gender
Men typically have higher BMRs than women because they tend to have more muscle mass and less body fat at the same weight.
Body size
Larger bodies need more energy to maintain basic functions. Height and weight both increase BMR, which is why they are key inputs in the formula.
Hormones
Thyroid hormones directly regulate metabolism. Hyperthyroidism can raise BMR by 50% or more, while hypothyroidism can lower it significantly.
Diet and fasting
Severe calorie restriction can lower BMR as your body adapts to conserve energy. This is one reason crash diets often fail long-term.
Is BMR the same as resting metabolic rate (RMR)?
Not exactly. BMR is measured under strict conditions after waking from 8 hours of sleep and 12 hours of fasting. RMR is measured under less strict conditions and is usually slightly higher. For practical purposes, the difference is small - typically 100-200 calories.
How accurate is the Mifflin-St Jeor equation?
Studies show it predicts BMR within about 10% of measured values for most people. It is more accurate than the Harris-Benedict equation, especially for obese individuals. However, it can be off for very muscular athletes or elderly people with significant muscle loss.
Can I increase my BMR?
Yes, but not dramatically. Building muscle through resistance training can raise BMR by 50-100 calories per day for each kilogram of muscle gained. High-intensity interval training (HIIT) can also boost metabolism for hours after exercise.
Should I eat at my BMR to lose weight?
No. Eating at your BMR means you are consuming only what your body needs at rest. For weight loss, aim for a calorie deficit based on your TDEE (total daily energy expenditure), not your BMR. Eating below your BMR for extended periods can slow metabolism and cause muscle loss.
Does BMR change during pregnancy?
Yes. BMR increases during pregnancy to support fetal growth and maternal tissue expansion. The increase is about 5-10% in the first trimester, 15-25% in the second, and 20-35% in the third trimester. Calorie needs should be discussed with a healthcare provider.
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