Daily calories by activity
The formula
How it works
Your Basal Metabolic Rate is the energy your body burns at complete rest just to keep you alive — breathing, circulation, keeping warm. It is the floor of your daily calorie needs, before any movement is added on top.
FAQ
BMR or TDEE — which should I use?
BMR is calories at rest. Your Total Daily Energy Expenditure (TDEE) multiplies BMR by an activity factor and is the number to use for eating to maintain, lose or gain weight.
Which formula is this?
The Mifflin-St Jeor equation, the current standard used by dietitians because it estimates BMR more accurately than older formulas for most people.
Is BMR the same as RMR?
They are close but not identical. Resting Metabolic Rate (RMR) is measured under slightly less strict conditions than BMR and runs a little higher, though in everyday use the two terms are often treated as interchangeable.
Why does muscle mass matter for BMR?
Muscle burns more calories at rest than fat tissue, so two people of the same weight can have different BMRs depending on body composition. Formulas based only on height, weight, age and sex can’t capture this, which is why very muscular or very lean people may see their real BMR differ from the estimate.
Can eating too little lower my BMR?
Yes. Prolonged, severe calorie restriction can trigger metabolic adaptation, where the body lowers its resting energy use to conserve fuel. This is one reason very aggressive diets often stall and why a moderate deficit is easier to sustain.
How much does BMR fall as I get older?
BMR tends to decline gradually with age, partly because muscle mass is typically lost over time. The formula already accounts for this through the age term, which is why an older person gets a lower estimate than a younger person of the same height and weight.
How do I use BMR to lose or gain weight?
Multiply your BMR by an activity factor to get your TDEE, then eat below it for weight loss or above it for weight gain. A deficit or surplus of around 300–500 calories a day is a common, sustainable starting point.
About the BMR calculator
This calculator estimates your Basal Metabolic Rate — the number of calories your body uses in a day if you did nothing but rest. Even asleep, your organs, brain and muscles need energy, and for most people that resting need is the largest single part of their daily calorie budget. Knowing it is the starting point for any plan to lose, gain or maintain weight.
How to use it
Choose your sex, enter your age, and pick metric or imperial units before typing your height and weight. A 30-year-old man who is 180 cm and 80 kg has a BMR of about 1,780 calories a day. Because the estimate depends on your real measurements, use current figures rather than rounded ones. The table below then multiplies your BMR by common activity levels to show roughly how many calories you would need to maintain your weight.
The formula
This uses the Mifflin-St Jeor equation, , where is weight in kilograms, is height in centimetres, is age in years and is a constant that is for men and for women. To get daily needs, multiply the result by an activity factor from about 1.2 for a desk-bound lifestyle up to 1.9 for hard daily training. That product is called your TDEE.
Where it is used
Dietitians and personal trainers use BMR to set calorie targets, and fitness apps use it behind the scenes to build meal and macro plans. It helps explain why two people of the same weight can need very different amounts of food, since age, height and sex all shift the number. As a resting baseline it is also used in clinical settings to estimate energy needs, though individual metabolism can vary by 5–10% from any formula.