Calorie Deficit Calculator

See when you will reach a goal weight on a daily calorie intake, or the intake a date needs.

Sex

Age

Height

Weight

Activity

Sedentary or light (PAL 1.40–1.69)

A job that takes little physical effort, getting about by car or bus, no regular exercise or sport, and most spare time spent sitting or standing.

Active or moderately active (PAL 1.70–1.99)Vigorous (PAL 2.00–2.40)

Goal weight

Work out

Daily calories

500 kcal under your maintenance to start with.

Choose a sex, then enter your age, height, weight and goal weight to see the result.

Works out when you reach a goal weight on a daily calorie intake, or the daily intake that reaches it by a date. It runs the dynamic model behind the NIH Body Weight Planner, which slows as your body adapts, and draws the familiar 3,500 kcal a pound rule beside it, week by week. Every calculation runs in your browser.

How to use it

Enter your sex, age, height, weight and activity, and your goal weight. Daily calories → date starts 500 kcal under your maintenance for a loss, or over it for a gain, until you enter your own; Target date → calories starts 12 weeks from today and takes a date from 7 days to 5 years ahead. A goal above your weight runs as a gain. The model is for adults who are not pregnant or breastfeeding, so it gives no result under 18 or with that box ticked.

How it works

The model of Hall and colleagues (2011) follows fat, lean tissue, glycogen and body water day by day. As weight falls, so does the energy the body burns: a smaller body costs less to run and to move, and the body partly adapts to eating less. A steady intake below maintenance therefore loses quickly at first and then more slowly, settling at a new weight rather than losing for ever. The first week moves fastest: the body's glycogen store, and the water held with it, shrinks or grows within days of a change in intake, before fat and lean tissue have moved much. The calculator ports the code of NIDDK's planner, with activity at FAO's worked example for the band (sedentary or light, 1.53), body fat estimated from BMI, age and sex, and carbohydrate at half of intake.

The 3,500 kcal rule (Wishnofsky, 1958) turns the gap between maintenance and intake into weight at a fixed rate that never slows. Over a few weeks the two lines are close; over months the rule promises far more than the body delivers. For a target date, the calculator finds the steady intake the model says reaches the goal on that day and rounds it to the 10 kcal that still does: down for a loss, up for a gain.

Examples

A man of 40, 178 cm, 95 kg, sedentary or light, aiming for 85 kg on 2,200 kcal a day

With Daily calories → date, the model reaches 85 kg in 22.6 weeks; the 3,500 kcal rule says 16.7. Holding 85 kg afterwards takes about 2,660 kcal a day.

A woman of 29, 163 cm, 72 kg, sedentary or light, aiming for 65 kg in 26 weeks

With Target date → calories and a date 26 weeks away, the intake is 1,780 kcal a day, against a maintenance of 2,190 kcal today. It reaches 65 kg on day 177.

Rules and sources

The model is from Hall and colleagues (Lancet, 2011), as NIDDK's Body Weight Planner implements it, and like the planner it is for adults who are not pregnant or breastfeeding. For a loss, an intake of 1,200 kcal a day or less carries a note: NICE NG246 calls 800 to 1,200 kcal a low-energy diet and under 800 a very-low-energy diet, both only within a specialist service with clinical support. A goal below a BMI of 18.5 is flagged as underweight. The rule is Wishnofsky's (1958) figure for weight lost on a high-protein, low-calorie diet; he found fasting losses held markedly less energy a pound.

Sources

Hall KD et al. Quantification of the effect of energy imbalance on bodyweight (Lancet 2011;378:826–837) — The Lancet
Body Weight Planner — NIDDK, National Institutes of Health
Wishnofsky M. Caloric equivalents of gained or lost weight (Am J Clin Nutr 1958;6:542–546) — American Journal of Clinical Nutrition
Overweight and obesity management (NG246), recommendations 1.16.8 to 1.16.11: low-energy and very-low-energy diets — NICE

Reviewed 20 October 2026

Frequently asked questions

Because the deficit shrinks. A lighter body burns less at rest and in movement, and the body adapts a little to eating less, so the same intake sits closer to the new maintenance each week. Keeping the original rate needs a lower intake over time; the chart shows how far a steady intake goes.

At a steady intake the model reaches a weight where intake and expenditure balance again. When that weight is short of your goal, the calculator gives it instead of a date; a lower intake, more activity, or a nearer goal reaches it.