Calorie Deficit Calculator

What this tool is used for

• Setting a daily calorie target for a weight goal.
• Seeing how large a deficit a target rate of loss implies.
• Comparing two rates of change on the same starting figures.
• Working out a maintenance figure before choosing a deficit.
• Producing a target to discuss with a professional.

Frequently Asked Questions

Where does the 3,500 calories per pound figure come from?

From the energy density of body fat, calculated by Max Wishnofsky in 1958. It is a useful first approximation and it is known to be wrong over time — the rule predicts linear loss forever, while real weight loss plateaus as a smaller body burns less.

What is a sensible rate of loss?

0.5 to 1% of body weight a week, which is roughly a 500 calorie daily deficit for most people. Faster than that costs disproportionate lean mass, and the evidence on adherence is clear that aggressive deficits are abandoned more often than they are completed.

Why does weight loss slow down even when the deficit is unchanged?

Because maintenance falls with body mass — a lighter body costs less to move and to maintain — and because adaptive thermogenesis reduces energy expenditure beyond that. A deficit calculated at the start becomes maintenance at a lower weight, which is the plateau.

Why did my weight go up during a deficit?

Almost always water. Glycogen binds roughly three grams of water per gram, and sodium, stress and menstrual cycles all move fluid by several pounds within days. Daily weight is noise around a trend, which is why weekly averages are the number to read.

Is a very low intake more effective?

Not sustainably. Below about 1,200 calories a day it becomes difficult to meet micronutrient needs, muscle loss accelerates, and adherence collapses. The best deficit is the largest one you will actually maintain, which is usually smaller than the one people choose.

Common errors and gotchas

• Choosing a deficit large enough to be unsustainable, which is the usual reason plans fail.
• Treating the BMR estimate as measured, when individual variation is substantial.
• Assuming a fixed 3,500 calories per pound, which is a simplification rather than a constant.
• Not recalculating as weight changes, since maintenance falls with it.
• Using it as clinical guidance rather than an estimate.