Because beyond about one percent of body weight a week an increasing share of the loss is muscle rather than fat, and the diet becomes harder to hold. The scale moves faster and the outcome is worse.

Why does progress slow down?

A lighter body costs less to run, and expenditure adapts downward during a sustained deficit. The same target is a smaller deficit three months in, so it needs recalculating.

Health & Fitnessnutrition

Daily Calorie Needs Calculator

A daily calorie target for a stated rate of loss or gain, with a floor below which the page will not go. Faster is not better: beyond about one percent of body weight a week, the extra loss comes disproportionately from muscle.

Also called: daily calorie needs, weight loss calorie calculator.

Daily calorie target

2,097

2,097 kcal a day at 0.5 kg a week, against maintenance of 2,647, a difference of 550. At 0.5 kg a week that is 0.67% of body weight, a rate the body can sustain from fat rather than lean tissue. The deficit is 550 kcal a day. Reaching 68 kg takes about 14 weeks at this rate. Expenditure falls as weight comes off, so the target needs recalculating every few kilograms rather than holding for the whole period.

Maintenance calories

2,647

Daily deficit or surplus

550

Weeks to the target weight

Floor this page will not go below

1,500

Low end of the estimate

1,887

High end of the estimate

2,306

On the rate

At 0.5 kg a week that is 0.67% of body weight, a rate the body can sustain from fat rather than lean tissue. The deficit is 550 kcal a day.

On the timeline

Reaching 68 kg takes about 14 weeks at this rate. Expenditure falls as weight comes off, so the target needs recalculating every few kilograms rather than holding for the whole period.

How this is calculated

Projected weight

Hover or drag for values

Weight, kg

Method and background

This is what the calculation gives for the numbers you entered. It is an estimate, not advice, and it knows nothing about your situation beyond those numbers. Rules for United States change on a published schedule; the effective date is shown on every rule-based tool.

How this is calculated

A kilogram of body tissue stores roughly 7,700 kcal, so half a kilogram a week is a deficit of about 550 a day. The arithmetic is easy and the constraint is biological: a deficit beyond roughly a quarter of maintenance takes an increasing share from lean tissue, and adaptive thermogenesis lowers expenditure as the diet continues, so the same target produces less loss in month three than in month one. The page floors the target at 1,500 kcal for men and 1,200 for women, the conventional lower bounds for an unsupervised diet, and says when a requested rate would have gone below them rather than printing a number nobody should eat to.

a kilogram of body tissue is about 7,700 kcal, so a rate in kilograms a week converts directly into a daily deficit

r: Kilograms a week

Worked examples

Each of these is asserted on every build. If a change to the engine ever moved one of these answers, the build would fail before the page could print it.

half a kilogram a week

Weight: 75 kg
Height: 178 cm
Age: 32
Sex: Male
Activity level: Moderately active, 3 to 5 days
Goal: Lose weight
Rate of change: 0.5 kg/week
Target weight: 68 kg

Daily calorie target2,097

7700 x 0.5 / 7 is a 550 kcal deficit

Open this example

a rate that would breach the floor

Weight: 60 kg
Height: 160 cm
Age: 45
Sex: Female
Activity level: Sedentary, desk work
Goal: Lose weight
Rate of change: 1 kg/week
Target weight: 55 kg

Daily calorie target1,200

boundary: the target is held at the floor rather than printed below it

Open this example

Method and limits

What it assumes

A constant 7,700 kcal per kilogram, which is an average across fat and lean tissue.

What it deliberately does not model

Expenditure falls as weight comes off, so the target needs revisiting every few kilograms.
Very low calorie diets belong under medical supervision and are outside what this page will produce.
Water weight moves faster than fat in the first fortnight, in both directions.

Formula version 1.0.0 · definition 1.0.0 · United States · Report a problem with this calculator

Frequently asked questions

Why not lose faster?: Because beyond about one percent of body weight a week an increasing share of the loss is muscle rather than fat, and the diet becomes harder to hold. The scale moves faster and the outcome is worse.
Why does progress slow down?: A lighter body costs less to run, and expenditure adapts downward during a sustained deficit. The same target is a smaller deficit three months in, so it needs recalculating.