Calorie Calculator

From one equation to a daily target: how the numbers are built

Every number this page shows is assembled from three simple layers, and knowing what each layer does tells you how much to trust it. The base layer is your resting burn (BMR) from the Mifflin-St Jeor equation. The second layer multiplies that by an activity factor to estimate a full day’s burn (TDEE). The third layer adds or subtracts a fixed amount to move your weight. The equation layer is the most reliable; the activity layer is where most of the error lives; the goal layer is pure arithmetic you control.

A worked example, layer by layer

Take a 34-year-old man, 5′10″ and 180 lb, who sits at a desk but trains two or three evenings a week. The calculator puts his resting burn at about 1,763 kcal— what he would burn lying still all day. Choosing “lightly active” multiplies that by 1.375 for a maintenance estimate of about 2,424 kcal. To lose a pound a week he would target roughly 1,924 kcal; to lose half a pound, about 2,174. Notice what a difference the activity choice makes: had he called himself sedentary, maintenance drops to 2,115 kcal — a 309-kcal swing, larger than the gap between “maintain” and “lose 0.5 lb a week”. Picking the honest activity level matters more than any other input on the page.

Why the 500-kcal rule works — roughly

The goal targets rest on an old approximation: a kilogram of body fat stores about 7,700 kcal, so a 500-kcal daily deficit should cost about half a kilogram (one pound) a week. In practice the rule is accurate early and optimistic later. As you lose weight, the body you are feeding gets smaller and burns less — the same 1,924-kcal intake that produced a 500-kcal deficit at 180 lb produces a smaller one at 165 lb. Water shifts also mask fat changes for weeks at a time, especially after changing carb intake. The practical fix is simple: weigh daily, average weekly, and recalculate your targets every few kilograms rather than treating the first number as permanent.

Choosing a deficit you can actually sustain

• Smaller deficits fail less. A 250-kcal deficit (0.5 lb/week) is easier to hold through holidays and restaurant meals than a 500-kcal one, and adherence — not the size of the deficit — predicts who actually loses weight over six months.
• Protect the floor.Prolonged intakes below roughly 1,200 kcal (women) or 1,500 kcal (men) make it hard to meet protein and micronutrient needs and tend to cost muscle as well as fat. If the calculator’s deficit target lands below the floor, take the slower goal instead.
• Gaining works the same way in reverse — a 250–500 kcal surplus supports muscle gain at 0.25–0.45 kg a week; beyond that, the extra is mostly stored as fat regardless of training.

Calories are the budget; the next questions are composition

A calorie target says how much to eat, not what. Once the budget is set, the macro calculator splits it into protein, carbs, and fat — protein being the piece that protects muscle in a deficit. The BMR calculator shows the resting layer in isolation with a second research equation for comparison, and the BMI calculator frames where your current weight sits for your height. If two to three weeks of honest tracking move your weekly average in the wrong direction, adjust intake by 100–200 kcal — your real maintenance is whatever the scale says it is, not what any equation predicts.