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About 3,500 calories per pound, or 7,700 per kilogram, is the familiar body-fat rule of thumb. It is useful to understand the convention, but it cannot tell you exactly when you will lose a pound or 5 kg.
NIDDK's Body Weight Planner models changes in energy expenditure and body weight instead of assuming a fixed loss forever. The NIH explanation of the planner describes why a changing body needs a changing estimate.
Body fat is not the same as pure dietary fat
Body-fat tissue contains lipid, water and other components. It is not a block of pure cooking fat. The energy associated with a change in body weight also depends on the mixture of tissue and fluid gained or lost.
| What is being described? | Approximate energy convention | Main limitation |
|---|---|---|
| One pound of body fat in common diet arithmetic | 3,500 kcal | A rule of thumb, not an exact tissue measurement |
| One kilogram using the same convention | 7,700 kcal | Does not predict an individual's weight-loss timing |
| One pound of pure dietary fat at 9 kcal/g | 4,080 kcal | A general food-energy factor, not a body-weight model |
One pound is about 453.6 g; 453.6 x 9 gives about 4,082 kcal for pure dietary fat. That helps explain why the answer changes when someone means body fat rather than fat as a nutrient. Actual foods have water and other components too: butter and cooking oil have different calories per gram.
Does a 500-calorie deficit mean losing a pound a week?
The arithmetic is 500 x 7 = 3,500. The physiological prediction is less certain. It assumes expenditure and the relationship between energy and scale weight remain constant.
As body weight, activity and intake change, expenditure can change too. Early weight changes can include fluid and stored carbohydrate rather than only fat. The scale cannot separate those components. An estimated 500-calorie difference on an app also does not prove that actual intake and expenditure differ by exactly that amount.
For these reasons, do not multiply a weekly prediction into a guaranteed completion date. The 5 kg guide explains how to think about a goal of roughly 11 lb without setting a crash-diet deadline.
What does an overnight gain mean?
A pound added to the scale is not automatically a pound of fat. Food and fluid in the body and measurement conditions can change weight. It is also not possible to label every sudden increase as entirely water from a scale reading alone.
Use comparable measurements if tracking is helpful, and interpret the longer pattern. See weight-loss plateaus and fluctuations. Do not compensate for a single reading by skipping meals or imposing a larger restriction.
How can you use the number sensibly?
Use it to understand a common convention and to spot unrealistic promises, rather than to calculate an exact personal finish date. For a starting expenditure estimate, the TDEE guide explains the equation and activity assumptions.
Food and weight records can help you review the plan. They do not cancel every logging error or become a direct measurement of metabolism. If a target seems ineffective, check the record and the assumptions before changing it. Get individual guidance for an appropriate weight-management plan when needed.
Frequently asked questions
How many calories are in a kilogram of body fat?
About 7,700 kcal is the common conversion derived from the 3,500-per-pound rule. It is approximate and cannot forecast a kilogram of scale change on a fixed timetable.
How long does it take to lose 10 pounds?
There is no fixed duration. CDC's general guidance favors gradual loss of about 1-2 lb per week, but that is not a personal deadline or a rate suitable for everyone. Body weight includes more than fat, and progress can change over time.
Can I lose a pound of fat in a day?
Do not use that as a target. A one-pound scale change does not identify a pound of fat loss, and trying to force a 3,500-calorie daily deficit can require extreme restriction or activity. Choose an appropriate plan rather than chasing one day's reading.