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Calorie Deficit Calculator

See how much weight a calorie deficit can lose.

Result

2.34 kg
5.15 lb
18,000 kcal

How it is calculated

The tool multiplies your average daily deficit by the number of days to get the total energy gap: total = deficit × days in kcal. It then applies the rule of thumb that 1 kg of body fat is about 7,700 kcal: loss (kg) = total / 7700. Pounds are kg × 2.20462.

Deficit is the number of calories below your maintenance level per day, not your intake. Both values must be greater than zero. This is a linear estimate: real weight changes also include water and muscle, and as the body adapts the same deficit usually yields less over time. The tool does not tell you how large a deficit is safe for you; very low intake needs a doctor or dietitian.

Worked example

A daily deficit of 600 kcal for 30 days. Total = 600 × 30 = 18,000 kcal. Fat loss = 18,000 / 7700 = 2.34 kg. In pounds: 2.34 × 2.20462 ≈ 5.15 lb. The tool shows 18,000 kcal, 2.34 kg and 5.15 lb.

Try this example →

Common mistakes

  • Entering your daily calorie intake in the deficit field instead of the shortfall below maintenance.
  • Expecting every kilo lost to be fat; early losses often include water.
  • Applying the same deficit over a very long period and assuming the rate stays constant.
  • Confusing kcal with the "calories" on food labels in kJ; 1 kcal is about 4.184 kJ.

Sources

About this calculator

This calculator estimates weight loss from a sustained calorie deficit using the commonly cited rule of thumb that roughly 7,700 kcal of deficit corresponds to about 1 kg of body fat lost (equivalently, about 3,500 kcal per pound). Multiply your daily deficit by the number of days and divide by that constant to get an estimated weight change.

Dietitians, personal trainers, and fitness enthusiasts use this kind of estimate for basic weight-loss planning, but it's important to treat it as a rough approximation rather than a precise prediction — actual fat loss slows over time due to metabolic adaptation, changes in lean mass, and water-weight fluctuations, so real-world results diverge from the simple linear math the longer the deficit is sustained. Enter your daily calorie deficit and the number of days to get an estimate. Hall et al. (Lancet, 2011) showed that this static rule overstates long-run change, because energy expenditure adapts as weight changes, so over months real change is slower than this projection.

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Comments (1)

  • Editorial team

    The deficit field means calories below your maintenance, so you need a reasonable maintenance figure first. Because maintenance falls as weight drops, a long run of identical days tends to overstate the loss. A practical use is to run it for two or three weeks, compare with your actual weight trend, and adjust the deficit. For very low intakes, speak with a doctor or dietitian. How did your measured change compare with the estimate?

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