Calories to pounds calculator

Published October 15, 2026 · Updated October 15, 2026

The famous 3,500 calorie rule dates from 1958 and it is wrong in a specific, predictable direction.

Where 3,500 came from

The figure comes from a 1958 estimate by Max Wishnofsky, who reasoned that a pound of body fat holds roughly 3,500 calories of energy. As chemistry that is broadly right. As a prediction of what happens to a human over six months, it is not.

Why the real result is slower

The rule assumes your body is a bank account with a fixed exchange rate. It is not. As you lose weight three things happen at once, and all three work against the arithmetic.

You become lighter, so everything you do costs less energy. Your body reduces its resting expenditure by more than the weight loss alone explains, a response usually called adaptive thermogenesis. And appetite rises, which quietly closes part of the deficit without any conscious decision.

The practical consequence is that a 500 calorie daily deficit does not produce a pound a week indefinitely. It does so at first, then flattens. Predicting six months of steady loss from the first fortnight is the most common way people conclude that their body is broken.

What to do with the number instead

Treat the figure above as an upper bound for the first month, then judge by the scale. Weigh yourself at the same time of day, take a weekly average rather than a daily reading, and adjust once every two or three weeks.

And expect the first week to look spectacular. Most of it is water and glycogen, and it comes back the moment carbohydrates do.