Your Basal Metabolic Rate (BMR) is the number of calories your body burns just to stay alive if you did nothing but rest in bed for 24 hours — no walking, no digesting food, no exercise. It covers the energy your heart, lungs, brain, kidneys and other organs need to keep functioning. This BMR calculator estimates that number in seconds from four inputs — sex, age, weight and height — using the Mifflin-St Jeor equation, the formula most widely recommended by dietitians and sports-nutrition researchers today because it is more accurate for modern populations than the older Harris-Benedict formula.
Knowing your BMR is the starting point for almost every serious nutrition decision: how many calories to eat to lose weight, maintain weight or build muscle. On its own, BMR only tells you the "engine idle" cost — you still need to add the calories burned by daily activity and exercise, which is covered further down this page.
The calculator uses the Mifflin-St Jeor equation, split by sex because men typically carry more muscle mass, which burns more calories at rest than fat tissue:
Each variable pulls in a different direction: more weight and more height raise your BMR (bigger body, more tissue to maintain), while more age lowers it (metabolism naturally slows a little each decade as muscle mass tends to decrease). The formula is a population average — genetics, muscle mass and hormone levels can shift your real number up or down by 5-10%, but for the vast majority of people it lands within a very usable range.
BMR alone is not "how many calories should I eat" — that number is your Total Daily Energy Expenditure (TDEE), which adds the calories burned by daily movement, digestion and exercise on top of BMR. Multiply your BMR by an activity factor to estimate it:
| Activity level | Description | Multiplier | Example TDEE (BMR 1,650) |
|---|---|---|---|
| Sedentary | Little or no exercise, desk job | ×1.2 | 1,980 kcal |
| Lightly active | Light exercise 1-3 days/week | ×1.375 | 2,269 kcal |
| Moderately active | Moderate exercise 3-5 days/week | ×1.55 | 2,558 kcal |
| Very active | Hard exercise 6-7 days/week | ×1.725 | 2,846 kcal |
| Extra active | Physical job or twice-daily training | ×1.9 | 3,135 kcal |
To lose weight, eat below your TDEE (a 500 kcal/day deficit ≈ 0.5 kg/week loss); to gain weight, eat above it. Use our Calorie Deficit Calculator to plan the deficit precisely.
Don't eat at or below your BMR for extended periods. That figure assumes zero activity; eating that little while living a normal life creates too large a deficit, which can slow metabolism and cause muscle loss. BMR is not TDEE. The single biggest mistake is using the BMR number as a daily calorie target — always apply an activity multiplier first (see the table above). Re-check periodically. BMR changes as your weight, age and muscle mass change, so recalculate every few months or after a significant weight change. Treat it as an estimate. Muscle mass, genetics, thyroid function and health conditions can shift real BMR by 5-10% either way — a metabolic-rate test (indirect calorimetry) is the only way to get an exact figure.
Basal Metabolic Rate is the number of calories your body burns at complete rest over 24 hours just to keep vital organs — heart, lungs, brain, kidneys — functioning. It does not include any calories burned through movement, exercise or digestion.
This calculator uses the Mifflin-St Jeor equation: for men, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age + 5; for women, BMR = 10×weight(kg) + 6.25×height(cm) − 5×age − 161. It is the formula most nutrition professionals recommend today.
BMR is the calorie cost of staying alive at rest. TDEE (Total Daily Energy Expenditure) is BMR multiplied by an activity factor to include walking, exercise, work and digestion — TDEE is the number you should actually use to set a calorie target.
No. Eating at or below your BMR for long periods is too aggressive for most people and can slow your metabolism and cause muscle loss. Instead, calculate your TDEE and create a moderate deficit (around 500 kcal/day) below that number.
Men typically carry more lean muscle mass than women at the same weight, and muscle burns more calories at rest than fat tissue. The Mifflin-St Jeor formula accounts for this with a +5 term for men and a −161 term for women.
Yes. The formula subtracts 5 calories per year of age, reflecting the gradual loss of muscle mass and slight metabolic slowdown that typically comes with aging, even if weight stays constant.
The Mifflin-St Jeor equation is considered the most accurate population-level formula available, typically within about 10% of BMR measured by indirect calorimetry in a lab. Individual factors like muscle mass, genetics and thyroid function can still shift your real number.
No. All calculations run directly in your browser using JavaScript. Nothing you enter is stored, transmitted or shared with any server.