Fitness calculators you can inspect.

The BMR calculator estimates resting energy from sex, weight, height, and age with the Mifflin-St Jeor equation, and shows a revised Harris-Benedict result from the same four inputs. The Katch-McArdle calculator estimates rest from lean body mass. Enter weight and a body fat percentage. It uses the Cunningham equation, under the Katch-McArdle name, with no sex, height, or age term. Choose it when you already have a body fat percentage. Choose the BMR calculator when you do not.

The TDEE calculator multiplies the Mifflin-St Jeor resting result by one activity factor. Enter sex, weight, height, and age in pounds and inches or kilograms and centimeters, plus a weekly activity level: sedentary, lightly active, moderately active, very active, or extra active. Basal expenditure times a physical activity level is the full-day method in the FAO/WHO/UNU human energy requirements. That activity-factor ladder does not come from the Mifflin paper. Use TDEE for a formula estimate of a typical day before you have an intake log. Leave out a separate session estimate when the activity factor already includes that training.

The maintenance calories calculator does not use sex, age, height, or an activity level. Enter average daily intake and weigh-ins, one date and weight per line, in pounds or kilograms. It fits a trend through the weigh-ins. Maintenance equals average intake minus that daily trend in kilograms times 7,700, the familiar 3,500 kcal per pound discussed by Hall. A falling trend is negative, so the result sits above logged intake. No number appears until the log covers at least 14 days and 8 weigh-ins. Those limits are an EVR rule of thumb. TDEE predicts from body data. This page reads the log. The two can disagree.

The calorie deficit calculator and the calorie surplus calculator both start from a maintenance number you enter, not from sex, height, or age. Deficit subtracts weekly pounds times 3,500, divided by 7, the static approximation associated with Wishnofsky. Surplus adds a planned daily surplus, with presets of +250 and +500 kcal per day, and shows a weekly figure from the same 3,500 kcal per pound step. Choose the deficit calculator when the target should sit below the maintenance number you entered, and the surplus calculator when it should sit above. Both pages cite Hall on why a fixed 3,500 kcal rule over-predicts long-term change.