How the target is calculated
The calculator finds your basal metabolic rate with the Mifflin-St Jeor equation, then multiplies it by an activity factor to reach total daily energy expenditure. Weight change targets are built from the widely used figure of roughly 7,700 kcal per kilogram of body fat, which puts a 0.5 kg weekly loss at about 550 kcal a day below maintenance.
Choosing the right activity level honestly
This is where most people overestimate. A desk job with three gym sessions a week is "light to moderate", not "very active". Walking 12,000 steps and doing manual work is moderate. The athlete multiplier is for people training twice a day, not for people who train hard once. Overstating activity is the most common reason a calorie target fails to produce the expected result.
What to do when the number does not work
Every equation here is a prediction, and predictions carry error. Eat at the calculated maintenance figure for two to three weeks, weigh yourself at the same time on the same days, and take the trend rather than any single reading. If weight is stable, the estimate was right. If it drifts, adjust by 100 to 200 kcal and repeat.
Calories are not the only thing
Protein preserves muscle in a deficit and is the most satiating macronutrient — roughly 1.6 g per kilogram of body weight is a well-supported target for people who train. Fibre, sleep and resistance training all affect how a deficit feels and how much of the loss comes from fat rather than muscle. The BMR calculator shows the resting energy these targets are built on, and the BMI calculator helps set a broad weight range.
A floor worth respecting
Intakes below roughly 1,500 kcal for men and 1,200 for women make it hard to meet micronutrient needs and are usually only appropriate under medical supervision. If your calculated deficit target falls below that, lose more slowly instead.