Calorie Deficit Calculator

Why faster is not better

An aggressive deficit does not simply produce the same result sooner. It changes what you lose. Beyond roughly 1,000 kcal/day the proportion of lean mass in the weight you lose rises, protein and micronutrient intake become hard to meet, and adherence collapses — which is why crash diets are followed so reliably by regain.

A slower deficit you can sustain for six months beats an aggressive one you abandon in five weeks. This is not a motivational point; it is the main determinant of the outcome.

Why the arithmetic overpromises

The 7,700 kcal-per-kg figure is a planning convention, not physiology. In practice weight loss runs slower than the maths predicts, because expenditure falls as you get lighter, water and glycogen shifts mask fat loss for weeks at a time, and reported intake is almost always an underestimate.

Expect the first two weeks to look dramatic (largely water), then a slower, noisier line. Judging progress on a weekly average rather than daily readings is the single most useful habit here.

Deficits and GLP-1 medication

GLP-1 medicines create a deficit by suppressing appetite rather than by willpower — which is why they work. The risk inverts: instead of struggling to eat less, people struggle to eat enough protein. Combined with an aggressive deficit, that is the fastest route to losing muscle along with fat. If you are on a GLP-1, set a conservative rate and prioritise protein.