How Long Does It Take to Lose a Pound of Fat?
A pound of body fat holds roughly 3,500 calories. At a 500-calorie daily deficit that is a week, in theory. In practice it slows down, and here is why the maths drifts.
In short
A pound of body fat stores about 3,500 calories, so a daily deficit of 500 calories should lose a pound a week. That holds early on and then slows, because a lighter body burns fewer calories, appetite rises, and people unconsciously move less. Losing one to two pounds a week is the sustainable rate; faster than that is mostly water and muscle.
The 3,500-calorie figure is older than most of the people using it, dating to a 1958 calculation, and it is roughly right about the energy in a pound of fat tissue. Where it goes wrong is the assumption that the body keeps burning the same amount as it shrinks.
The simple version
A pound of fat tissue holds about 3,500 calories. Eat 500 fewer than you burn each day and after seven days you have a 3,500-calorie shortfall, which the body makes up from stored fat. One pound a week.
That arithmetic is correct for the first few weeks. Then three things happen.
Why it slows
A smaller body burns less. Every kilo you lose is a kilo you no longer carry around, heat or maintain. Resting metabolism falls with body weight, and so does the cost of movement. After losing 10 kg, the same daily intake that was a 500-calorie deficit might now be a 300-calorie one.
Appetite rises. Hormones that signal hunger increase and those that signal fullness decrease during weight loss, and the effect persists. This is not weakness. It is the body defending its previous weight, and it is why maintaining a deficit gets harder rather than easier.
Movement drops. People in a deficit unconsciously fidget less, sit more and take the lift. Studies measuring total daily activity find this compensation absorbs a meaningful share of any intended deficit, without the person noticing.
Put together, the honest expectation is something like: a pound a week for the first month or two, then closer to half a pound as the body adapts, unless intake is reduced again.
The first week is not fat
Cutting calories, particularly carbohydrate, uses up glycogen, the stored form of carbohydrate in muscle and liver. Each gram of glycogen holds around three grams of water. Emptying those stores drops two to four pounds of water in days.
That early drop is real weight but not fat, and it returns the moment carbohydrate intake goes back up. Anyone who has lost five pounds in a week and regained three after a weekend has seen glycogen refill, not fat return.
What a sustainable rate looks like
Health guidance recommends 0.5 to 1 kg a week, about one to two pounds. Faster loss usually means a deficit large enough to cost muscle as well as fat, and to be abandoned. Slower is fine and often sticks better.
At a realistic long-run rate of half to one pound a week, losing 10 kg takes five to ten months. That is longer than most plans promise and closer to what most people actually experience.
Making the arithmetic work
- Recalculate your calorie target every 5 kg, since the old one no longer produces a deficit.
- Weigh yourself weekly rather than daily, and look at the trend over a month. Daily water swings of a kilo are normal and meaningless.
- Keep protein high and lift something, to hold on to muscle while fat comes off.
- Expect plateaus. A fortnight with no change is not failure; it is the point where the deficit needs adjusting.
The 3,500-calorie rule is a good starting estimate and a poor long-term forecast. Treat the first number it gives you as an opening bid.
Common questions
Why did I lose more than a pound in the first week?
The early drop is largely water. Cutting calories, especially carbohydrate, reduces stored glycogen, and each gram of glycogen holds about three grams of water. Two to four pounds in week one is common and mostly not fat.
Why has my weight loss stalled?
Usually because the deficit has shrunk. A lighter body needs fewer calories, so the same intake that produced a deficit at the start may be maintenance now. Recalculate your target every few kilos, and check whether portion sizes have drifted.
Is it better to eat less or exercise more?
For creating a deficit, eating less is more reliable, because burning 500 calories takes about an hour of hard exercise and the body compensates by increasing appetite. Exercise is better for keeping weight off and for health generally. Do both, but expect diet to do most of the arithmetic.
Sources
Every factual claim above traces to one of these. Follow them rather than taking this article's word for it.
Try it yourself
Free, instant, and nothing you enter leaves your browser.