About 7,700 calories (roughly 32,000 kJ) is the usual estimate for 1 kg of body fat. Here is where the number comes from, how long it takes to lose a kilo at different deficits, and why the scale does not always agree.
A commonly used estimate is that 1 kg of body fat holds about 7,700 calories (kcal), which is roughly 32,000 kilojoules (7,700 × 4.184 = 32,217 kJ). It is a rule of thumb, not an exact figure, and real weight loss is rarely a straight line.
Body fat tissue is not pure fat; it also contains water and other tissue. Fat provides about 9 kcal per gram, and the widely quoted figure for a kilogram of body fat tissue works out at around 7,000 to 7,700 kcal. Many calculators round it to 7,700.
| Daily deficit | Days to lose 1 kg (estimate) | Weeks |
|---|---|---|
| 250 kcal (1,046 kJ) | 31 days | 4.4 weeks |
| 500 kcal (2,092 kJ) | 15 days | 2.2 weeks |
| 750 kcal (3,138 kJ) | 10 days | 1.5 weeks |
| 1000 kcal (4,184 kJ) | 8 days | 1.1 weeks |
A deficit of about 550 kcal (2,300 kJ) a day adds up to roughly 3,850 kcal a week, or about 0.5 kg of fat per week on paper.
Large deficits are hard to sustain and can cost muscle. See what is a good calorie deficit for sensible ranges, and speak to a doctor or dietitian before starting a significant weight-loss plan.
The calorie deficit calculator turns your goal and timeframe into a daily target. Use the kJ to calories converter to switch between kJ and kcal.
Set a goal and see the daily target it implies.
Open the Calorie Deficit CalculatorHow many calories are in 1 kg of fat?
About 7,700 calories (kcal) is the commonly used estimate, which is roughly 32,000 kJ. It is a rule of thumb.
How many kilojoules are in 1 kg of fat?
About 32,000 kJ (7,700 kcal × 4.184).
How many calories do I need to burn to lose 1 kg?
About 7,700 calories of deficit over time. A deficit of 500 kcal a day takes roughly 15 days on paper.
Is losing 1 kg a week safe?
That needs a deficit of about 1,100 kcal a day, which is large for many people. Speak to a doctor or dietitian before aiming for a rate like that.
Why am I not losing weight at the expected rate?
Water, muscle changes, tracking errors and a slowing metabolism all affect results. Look at the trend over weeks, not days.