Calorie deficit calculator: the gap, and what it implies

Daily deficit against an estimated maintenance of 2,759 kcalworked example

500 kcal

Intake this implies: 2,259 kcal
Share of your maintenance estimate: 18.1%
Weekly rate under the 1958 rule: 0.45 kg3,500 kcal per pound — an upper bound, not a forecast
Over a year, with adaptation: 11.3 kg – 22.7 kgThe straight line alone would say 23.7 kg

A deficit is a difference between two figures, and the one it is measured against is an estimate carrying a ±10% band. That means 500 kcal against a maintenance estimate of 2,759 kcal could really be anywhere from 224 kcal to 776 kcal. The scale settles it; the equation only starts the conversation.

Which do you have?

Maintenance calories (kcal/day)Do not have one? The TDEE calculator estimates it, and the link is below.Daily deficit (kcal/day)No size is recommended here, deliberately. The table below shows what several common figures imply.

Resting estimate (optional, kcal/day)Only used to tell you when the intake target has dropped below your own resting figure. The BMR calculator produces it.

Realistic range

11.3 kg to 22.7 kg

The 3,500 kcal per pound rule assumes two things that are not true: that every kilogram lost carries the same energy, and that the body needs as much energy at a lighter weight as it did at a heavier one. Hall (2008) showed the first depends on how much body fat a person starts with, and Hall and colleagues (2011) found that a sustained change in intake produces only about half of its eventual weight change in the first year. A straight-line figure is therefore a ceiling on what the arithmetic allows, not a forecast of what happens.

What several common deficits imply against a maintenance figure of 2,759 kcal
Deficit	Intake	Weekly rate (1958 rule)	12 weeks, as a range
250 kcal/day	2,509 kcal	0.23 kg	1.3 kg – 2.7 kg
500 kcal/day	2,259 kcal	0.45 kg	2.6 kg – 5.4 kg
750 kcal/day	2,009 kcal	0.68 kg	3.9 kg – 8.2 kg
1000 kcal/day	1,759 kcal	0.91 kg	5.2 kg – 10.9 kg

Weekly rate from Wishnofsky 1958. The 12-week range spans the adaptation-aware low end (Hall 2011 anchors) and the straight-line high end, capped at the eventual change the rule of thumb implies. No row here is a recommendation.

Need the maintenance figure first? The TDEE calculator estimates it from four inputs. To see the same gap projected over months rather than a year, use the weight loss calculator.

A calorie deficit is the gap between the energy you use and the energy you eat. This calculator works out that gap from your estimated maintenance figure, converts it using the 3,500 kcal per pound rule, and shows the correction Hall published in 2008 for why that rule overstates things.

Resting energy expenditure (Mifflin-St Jeor) — BMR (kcal/day) = 10 x weight(kg) + 6.25 x height(cm) - 5 x age(y) + 5 (male) or - 161 (female). Verified 2026-07-30 against Mifflin et al., Am J Clin Nutr 1990 (Derived from 498 healthy adults aged 19 to 78. It landed within 10% of measured resting metabolic rate for more people than any other equation in the Frankenfield 2005 review, which also means it missed by more than 10% for some of them.)
Activity multipliers for total daily energy expenditureconvention — TDEE = BMR x activity multiplier (1.2, 1.375, 1.55, 1.725 or 1.9). Verified 2026-07-30 against FAO/WHO/UNU, Human energy requirements (2004) - the documented PAL framework this ladder approximates (No primary source publishes this ladder and no error term was ever attached to it. Choosing one rung rather than its neighbour moves the answer by roughly 200 to 300 kcal/day, which makes it the largest single source of disagreement between two calculators given the same body.)
The 3,500 kcal per pound rule (Wishnofsky) — 1 lb of body weight = 3,500 kcal, or about 7,716 kcal per kg. Verified 2026-07-30 against Wishnofsky, Am J Clin Nutr 1958 (Rests on the tissue lost being mostly fat of constant composition, and on energy needs staying the same at a lighter weight. Hall 2008 and Hall 2011 show both assumptions fail, so a straight-line figure is a ceiling rather than a forecast.)
Required energy deficit per unit weight loss (Hall) — the energy density of lost weight is not constant: more initial body fat means a larger cumulative deficit per kg lost. Verified 2026-07-30 against Hall, Int J Obes 2008 (A modelling result checked against published weight-loss data in lean and obese subjects. The 3,500 kcal per pound rule approximately matched only above roughly 30 kg of initial body fat, and overestimated the deficit required below that.)
Eventual weight change per sustained change in intake (Hall) — about 1 kg of eventual change per 100 kJ/day, or 10 kcal/day per pound; about half of it within 1 year and about 95% within 3 years. Verified 2026-07-30 against Hall et al., The Lancet 2011 (A rule of thumb for an average overweight adult, not a personal trajectory. This site interpolates linearly between the published 1-year and 3-year anchors and holds at 95% beyond three years rather than extrapolating past what was published.)

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Frequently asked questions

How do you calculate a calorie deficit?

Subtract intake from maintenance. Maintenance here is a resting figure from the Mifflin-St Jeor equation multiplied by an activity factor, so the deficit inherits every bit of that estimate uncertainty: a 500 kcal deficit against a figure that could be 300 kcal out is not a precise 500.

How much weight does a 500 calorie deficit mean?

Under the 3,500 kcal per pound rule from 1958, 500 kcal a day for seven days is exactly one pound, or 0.45 kg. Hall showed in 2008 that this rule matches only for people starting with a lot of body fat, and that a straight line overstates what follows for everyone else.

Why does a deficit stop working after a while?

Because it shrinks without you changing anything. A lighter body needs less energy, so the same intake is a smaller gap each month. Hall and colleagues found in 2011 that about half of the eventual change from a sustained intake change arrives in the first year, and about 95 percent by three.

What size deficit should I use?

This tool will not answer that, and no calculator honestly can: the right answer depends on your medical history, medications, training and what you can sustain. What arithmetic can tell you is what any given deficit implies, and when the resulting intake target has dropped below your own resting estimate.

Is it better to eat less or move more?

Arithmetically the two are interchangeable, since a deficit is a difference between two figures. Physiologically they are not, and the evidence on that is a clinical question rather than a calculator one. The tool shows you the gap and stops there.

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The next number

No body metric means much on its own. Here is what this one feeds into.

Weight loss calculatorSee the same deficit projected over months as a range, with the adaptation correction applied.Protein calculatorThe ISSN notes protein needs run higher while energy intake is restricted, and that range is per kilogram.

Related calculators

Weight loss calculatorEnergy balance Maintenance calorie calculatorMetabolism TDEE calculatorMetabolism

Every formula on this page is listed with its source on the methodology page, and changes to any reference value are logged in the data changelog. Canonical URL: https://myhealthmywellness.com/calorie-deficit-calculator