How much of a deficit equals one kilogram of fat?

Roughly 7,700 calories. So a 550-calorie daily deficit adds up to about 0.5 kg of fat a week.

Why am I in a deficit but not losing weight on the scale?

Day-to-day weight is mostly water, food in transit and glycogen. Fat loss can be real while the scale holds flat for a week or two. The trend over 2–4 weeks is what matters.

The science

How a calorie deficit causes weight loss (the actual mechanism)

Why eating less than you burn makes you lose fat: energy balance, the 7,700 kcal-per-kg rule, and why the scale jumps around even when you’re doing everything right.

A calorie deficit causes weight loss because your body has to fund the shortfall from somewhere, and the biggest store it holds is fat. That's the entire mechanism. Knowing how it works makes the whole thing less mysterious, and much easier to stick with in the week the scale misbehaves.

Energy in, energy out

Your body runs on energy, measured in calories. Every day it spends a certain amount keeping you alive and moving: your total daily energy expenditure, or TDEE. Food puts energy back in.

When you eat less than your TDEE, you create a shortfall. Your body can't just stop (your heart still beats, your brain still runs), so it covers the gap by breaking down stored energy. The biggest store, by far, is body fat.

Fat isn't a punishment. It's your body's savings account. A calorie deficit is simply spending from it.

The 7,700 number

Body fat is energy-dense. One kilogram of it holds roughly 7,700 calories.

7,700 kcal ≈ 1 kg of fat

So a 550 kcal daily deficit ≈ 0.5 kg of fat per week

That's why a sane, moderate deficit produces steady-but-not-dramatic loss. A 550-calorie daily deficit, held for a week, adds up to about 3,850 calories, roughly half a kilo of fat. Try to lose much faster than that and you start sacrificing muscle and water instead of fat, which is exactly the wrong trade. We unpack that in why crash diets fail.

Why the scale lies to you (for a while)

Fat loss and scale weight are not the same thing day to day. That gap is where most people lose their nerve.

On any given morning the scale is reading mostly water, the food still moving through you, and stored carbohydrate (glycogen), which each gram holds water alongside. Eat a salty meal, train hard, or simply sleep badly, and the scale can jump a kilo overnight, while your actual fat is quietly going down.

This is normal. The fix is patience and a longer lens:

Day to day: noise. Ignore it.
Week to week: a signal starts to show through the noise.
Over 2–4 weeks: the trend, which is the only figure worth reacting to.

We go deeper on stalls and overnight spikes in plateaus, scale jumps and rebound.

What to do with that

Set a deficit you can hold, eat enough protein to keep the muscle you already have, then leave the scale alone for a fortnight before you decide anything about it. The mechanism doesn't need supervision. It needs time, and a number you're still eating to in three weeks.

Common questions

How much of a deficit equals one kilogram of fat?: Roughly 7,700 calories. So a 550-calorie daily deficit adds up to about 0.5 kg of fat a week.
Why am I in a deficit but not losing weight on the scale?: Day-to-day weight is mostly water, food in transit and glycogen. Fat loss can be real while the scale holds flat for a week or two. The trend over 2–4 weeks is what matters.