Find your Basal Metabolic Rate — the number of calories your body burns at complete rest — and see your total daily calorie needs based on activity level.
Your Basal Metabolic Rate is the number of calories your body needs just to keep the lights on — breathing, circulating blood, repairing cells, and maintaining organ function — while lying completely still and digesting nothing. It doesn't include any calories burned through movement, exercise, or digesting food, which is why BMR is always noticeably lower than the total number of calories most people burn in a day.
BMR typically makes up 60–75% of total daily calorie burn for most people, with the rest coming from physical activity and the energy used to digest food (known as the thermic effect of food).
This tool uses the Mifflin-St Jeor equation, which is generally considered more accurate than older formulas like Harris-Benedict for most adults:
To estimate your total daily calorie needs, your BMR is then multiplied by an activity factor ranging from 1.2 (sedentary) to 1.9 (extremely active), giving your Total Daily Energy Expenditure, or TDEE.
Once you know your TDEE, weight management essentially comes down to comparing it to how much you actually eat. Eating close to your TDEE keeps your weight roughly stable. A consistent deficit of around 500 calories a day below your TDEE tends to produce about half a pound of fat loss per week, since one pound of body fat is roughly equivalent to 3,500 calories. The same logic works in reverse for anyone trying to gain weight.
| Goal | Approach |
|---|---|
| Maintain weight | Eat close to your TDEE |
| Lose ~0.5 lb/week | Eat about 500 calories below TDEE |
| Gain ~0.5 lb/week | Eat about 500 calories above TDEE |
Keep in mind BMR formulas are population averages — muscle mass, genetics, hormone levels, and certain medical conditions can shift your real metabolic rate up or down from what any formula predicts. Use this as a starting point, then adjust based on how your actual weight responds over a few weeks.