How Many Calories to Lose a Pound?

About 3,500 calories is the figure everyone quotes for a pound of body fat, which makes a 500-a-day deficit work out to roughly a pound a week.

It is a reasonable place to start. It is also, over any long period, wrong in a predictable direction — and knowing which direction saves a lot of frustration.

Where 3,500 came from

A pound of body fat stores roughly 3,500 kcal of usable energy. The rule was published by Max Wishnofsky in 1958 and has been repeated ever since.

The arithmetic is sound. The assumption underneath it is not: it treats your body as a container with a fixed energy price, where removing 3,500 calories always removes exactly one pound, forever.

Why it overstates long-term loss

Two things happen as you lose weight, and both reduce the deficit you are actually running.

You get smaller, so you burn less. A lighter body costs less to maintain and less to move. Someone who has lost 20 lb burns roughly 100 fewer calories a day doing exactly what they did before. The deficit that produced the loss shrinks as the loss accumulates.

Adaptive thermogenesis. Beyond the arithmetic of a smaller body, sustained restriction reduces energy expenditure a little further — via lower non-exercise movement, small hormonal changes, and slightly more efficient activity. The effect is real, modest, and frequently exaggerated in both directions.

The practical consequence: a 500-a-day deficit produces close to a pound a week at first, then progressively less. Predicting 52 lb in a year from it will be wrong. Plateaus are the expected behaviour of the system, not a sign you have done something wrong.

Estimate your own maintenance figure with the calorie calculator, or see the underlying metabolic rate in the BMR calculator.

What a deficit actually looks like

Daily deficit	Early rate	Realistic over 6 months
250 kcal	~0.5 lb/week	Slow, very sustainable
500 kcal	~1 lb/week	The standard recommendation
750 kcal	~1.5 lb/week	Aggressive; hard to sustain
1,000 kcal	~2 lb/week	Usually too much for most people

Larger deficits lose more weight and a higher proportion of it from muscle, and they are markedly harder to maintain. The deficit you actually stick to beats the one that is theoretically faster.

Every number in this is an estimate

This is the part worth internalising, because it explains most of the confusion people have with their own results.

• Calorie counts on labels are allowed to be out by up to 20%, and are calculated from composition rather than measured.
• Your maintenance requirement from any calculator carries roughly a ±10% error — for a 2,000 kcal estimate, that is 200 calories, which is most of a standard deficit.
• Absorption varies. Cooking, processing and fibre all change how much energy you extract from the same food.
• Scale weight moves for reasons unrelated to fat. Water, glycogen, sodium and the digestive tract routinely swing daily weight by several pounds.

Which is why the useful measurement is not today's weight but the trend over two to three weeks. A single weigh-in carries more noise than signal.

The practical version

Pick a deficit you can hold, track the weekly average rather than the daily number, and adjust based on what actually happens over a month rather than what the arithmetic predicted.

If the trend stalls for three weeks at a genuinely consistent intake, the deficit has closed — because you are smaller now — and it needs resetting. That is the system working as designed, not failing.

And weight alone is a poor measure of what is changing underneath it. BMI vs body fat percentage covers why two people at identical weight can be in very different condition.

General information only. Not medical or dietary advice — talk to a doctor or dietitian before starting a substantial deficit, particularly with any existing health condition.