Calorie Deficit Calculator

How big a deficit gives the rate of loss you want.

Calculate the daily calorie deficit needed for a target rate of weight loss, and see whether that target is realistic and safe.

Written and maintained by Mohit PatelLast checked August 4, 2026How we build these

Units

Maintenance calories (TDEE)

kcal

Current weight

Target loss per week0.5 kg

Daily calorie target

1,850 kcal

550 kcal below maintenance

Deficit per day550 kcal

Deficit per week3,850 kcal

Rate as % of body weight0.71% per week

Loss per month2.2 kg

How the Calorie Deficit Calculator works

A pound of body fat stores roughly 3,500 calories, and a kilogram about 7,700. Divide the deficit you can sustain into that figure and you get a rate of loss. The arithmetic is simple; the part people underestimate is that bigger deficits do not scale linearly, because they cost muscle and adherence.

Also known as: weight loss calorie deficit · deficit for losing weight · how big a deficit to lose a pound

The 3,500 calorie rule, and why it fails

The rule that a pound of fat is 3,500 calories, so a 500 calorie daily deficit produces a pound a week, is the most widely repeated figure in weight management and it is wrong beyond the first few weeks.

It comes from the energy density of adipose tissue and it assumes that energy expenditure stays constant as weight falls. It does not: a lighter body costs less to move and less to maintain.

The consequence is that a fixed deficit produces decelerating weight loss and eventually a plateau at a new maintenance weight. The predicted loss from the linear rule can exceed actual loss substantially over a year.

Choosing the size of the deficit

A deficit of roughly 0.5% to 1% of body weight per week is a commonly recommended range, which for an 85 kilogram person is 425 to 850 grams a week.

Larger deficits produce faster loss and cost more lean mass, more adherence difficulty and more metabolic adaptation. Smaller deficits are easier to sustain and slower.

The higher end of the range is more appropriate for people with more to lose, and the lower end for those closer to their target, where preserving lean mass matters more and the available fat stores can support less aggressive mobilisation.

Protecting lean mass

Weight lost in a deficit is a mixture of fat and lean tissue, and the proportion depends on how the deficit is run.

Two things reliably shift the ratio towards fat: adequate protein, at the higher end of the ranges discussed above, and resistance training. Both are well supported and their effects are additive.

Without either, a meaningful proportion of weight lost can be lean tissue, which reduces the metabolic rate further and makes the weight easier to regain. That is a large part of why aggressive diets without training have such poor long-term outcomes.

The plateau, and what it means

A plateau after several weeks or months is expected rather than a failure. It happens because expenditure has fallen to meet intake, through lower body mass, lower non-exercise activity and metabolic adaptation.

The options are to recalculate the deficit against current weight, to increase activity, or to take a planned break at maintenance before resuming.

The response that usually goes wrong is cutting further immediately. Deficits that were already meaningful become severe, adherence collapses, and the resulting rebound undoes the progress. Recalculating and continuing at the same relative deficit is nearly always the better move.

Reading the scale correctly

Daily weight moves with fluid, food volume, glycogen and hormonal cycle by a kilogram or more, which is larger than a week's genuine fat loss.

Which means daily weights are noise and weekly averages are signal. Weighing every morning under the same conditions and averaging the week gives a figure that can be compared meaningfully with the previous week.

It also explains the frustrating pattern where weight holds for two weeks and then drops suddenly. Fat loss was occurring throughout; fluid retention was masking it, and the drop is the mask coming off rather than the fat leaving in a day.

Where to go next

The Calorie Deficit question rarely arrives on its own. These are the ones that usually come with it:

TDEE Calculator — Total daily energy expenditure and what each part contributes.
Goal Weight Date Calculator — When you will reach your target weight at your current rate.
Calorie & BMR Calculator — Daily calorie needs for losing, holding, or gaining weight.
BMI Calculator — Body mass index with category and healthy weight range.

Sources

Not medical advice. This calculator gives a general estimate, not medical advice. It cannot account for your individual health, medical history, or medication. Talk to a qualified healthcare professional before acting on any result.

Frequently asked questions

How big should my calorie deficit be?

A useful rule is 0.5-1% of body weight lost per week, which for most people means a deficit of 300-750 calories a day. Leaner people should sit at the lower end; there is less fat available to mobilise, so an aggressive deficit takes the difference from muscle.

Is the 3,500 calories per pound rule accurate?

As a starting estimate, roughly. As a long-run predictor, no; it assumes your expenditure stays fixed, but a smaller body burns less, so real loss decelerates and plateaus below what the linear rule predicts. Expect to reduce intake or increase activity again after several weeks.

Why has my weight stopped falling in a deficit?

Most often intake has crept up without being noticed, or expenditure has fallen because a smaller body costs less to run and dieting quietly reduces spontaneous movement. Water retention can also mask several weeks of genuine fat loss on the scale. Track a 7-day rolling average rather than daily readings.

What is the smallest safe calorie intake?

Commonly cited floors are about 1,200 calories a day for women and 1,500 for men, below which meeting micronutrient needs becomes difficult without supervision. Very low calorie diets exist clinically but are monitored for good reason.