How this calculator works
The calculator uses the common approximation that one kilogram of body fat stores about 7,700 kcal. A pace of 0.5 kg per week therefore needs a deficit of 3,850 kcal per week, or 550 kcal per day. It then estimates the energy used by one exercise session from the activity MET, current body mass and time, multiplies by sessions per week, and reports how much of the weekly deficit exercise could supply. The rest has to come from a lower intake. This is a planning model: real weight change slows as body mass falls and as the body adapts. It also uses the current weight for every session, so the exercise calories are an upper estimate.
Formula
Weight to lose = current weight - target weight. Weeks = weight to lose / pace in kg per week. Required daily deficit = pace x 7,700 / 7. Session calories = MET x 3.5 x current weight / 200 x minutes. Exercise share = (session calories x sessions per week) / (pace x 7,700). Remaining daily deficit = max(0, (weekly deficit - weekly exercise) / 7).
Worked example
Going from 90 kg to 80 kg at 0.5 kg per week means losing 10 kg over 20 weeks, with a required deficit of 550 kcal per day. Walking 60 minutes three times a week at 3.5 METs burns 5.51 kcal/min, or 330.75 kcal per session. That is 992.25 kcal a week, or 25.77 percent of the 3,850 kcal deficit, leaving 408 kcal a day to remove from intake.
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Frequently asked questions
Is 7,700 kcal per kilogram exact?
No. It is an approximation for fat tissue and ignores changes in water, glycogen and lean mass. It is useful for planning and becomes less accurate over long periods and at low body mass.
Why does the timeline tend to be longer?
A lighter body burns fewer calories for the same activity, and appetite and metabolic adaptation can reduce the deficit. The linear forecast is a starting estimate, not a promise.
Should I rely on exercise alone?
Exercise helps but is easier to out-eat than most people expect. A combination of a modest intake deficit and regular activity is more sustainable, and it preserves muscle better than a very low intake alone.