Calorie Deficit Calculator (Weekly Loss and the 3,500-Calorie Rule)
Daily calorie deficit from TDEE and target intake, the early weekly loss by the 3,500-calories-a-pound (7,700 kcal/kg) rule, and what the NIH weight model says happens over a year.
Inputs
- TDEE
- 2,500 kcal/day
- Target intake
- 2,000 kcal/day
- % of TDEE
- 20.0%
- Early weekly change (7,700 kcal/kg rule)
- −0.45 kg (500 × 7 ÷ 7,700)
- After about a year (NIH model rule)
- −10.5 kg
- Eventual change, after about 3 years
- −20.9 kg
- What the 7,700 rule would claim for a year
- −23.7 kg
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What each Calorie Deficit input means
- TDEE (kcal/day)
- Calories you burn in a typical day. The maintenance-calories page estimates it from your measurements; a few weeks of steady weight on a known intake measures it better.
- Target intake (kcal/day)
- Calories you plan to eat. A target above TDEE shows a surplus and a gain instead.
- Show weight in
- Show weight change in kilograms or pounds. Calories are the same either way.
Calorie Deficit formula
Deficit = TDEE − target intake · Early weekly loss ≈ deficit × 7 ÷ 7,700 kcal per kg (3,500 per lb) · Eventual loss ≈ deficit ÷ 23.9 kcal per kg, about half of it in the first year
A calorie deficit is the gap between what you burn in a day (your TDEE) and what you eat. The old rule of thumb turns it into weight with 7,700 kcal per kilogram of fat, or 3,500 per pound, so a 500 kcal daily deficit is about 0.45 kg or 1 lb a week. That rule is fair for the first weeks and badly wrong over a year, because as you lose weight you burn less, and the deficit shrinks on its own. Kevin Hall's team at the NIH modelled this in The Lancet in 2011 and gave a simpler rule for an average overweight adult: every 100 kJ (about 24 kcal) a day of reduced intake eventually takes off about 1 kg, with half of that reached in about a year and nearly all of it in about three. The page shows both: the early weekly pace by the old rule, and the one-year and eventual figures by Hall's rule, next to what the old rule would claim for the year. The CDC's guidance of 1 to 2 pounds a week is flagged if the early pace runs faster.
Calorie Deficit worked example
Maintenance at 2,500 kcal a day and a target of 2,000 gives a 500 kcal daily deficit, 20% of TDEE. By the 7,700 rule that is 500 × 7 ÷ 7,700 = 0.45 kg a week at first. Hall's rule says the same deficit, held, eventually takes off 500 ÷ 23.9 = 20.9 kg, about 10.5 kg of it in the first year — less than half the 23.7 kg the 7,700 rule would claim for a year.
More Calorie Deficit examples
A modest 250 kcal daily deficit from a 2,200 TDEE: 250 × 7 ÷ 3,500 is half a pound a week to begin with. Over a year Hall's rule expects about 11.5 lb, and about 23 lb eventually, against 26 lb a year by the old rule — slow, but a 250 kcal deficit is easy to keep.
Eating 1,800 against a TDEE of 3,000 is a 1,200 kcal deficit, 40% of maintenance — about 1.1 kg (2.4 lb) a week early on, faster than the CDC's 1 to 2 pounds, so the page flags it along with the 1,000 kcal caution.
Where the Calorie Deficit calculator can give the wrong answer
- Hall's figures are for an average overweight adult holding the same intake. A smaller or lighter person reaches a new steady weight sooner, and the larger deficits in the table assume a starting weight with that much to lose.
- The scale moves faster than any rule in the first week or two, mostly water and stored glycogen, then slows. Judge progress over four weeks or more.
- TDEE is an estimate, often 10% off. If weight is not moving after a month, the real deficit is smaller than the planned one.
- Very large deficits (over about 1,000 kcal a day) cost more muscle, are hard to sustain and should be discussed with a doctor, especially at low intakes.
- The rules assume intake stays fixed. In practice people eat a little more as weight comes off, which is the main reason losses slow beyond what the model expects.
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Calorie Deficit reference table
| Daily deficit | Week 1 (7,700 rule) | First year (Hall) | Eventual (Hall) |
|---|---|---|---|
| 250 kcal | 0.23 kg (0.5 lb) | 5.2 kg (11.5 lb) | 10.5 kg (23 lb) |
| 500 kcal | 0.45 kg (1.0 lb) | 10.5 kg (23 lb) | 20.9 kg (46 lb) |
| 750 kcal | 0.68 kg (1.5 lb) | 15.7 kg (35 lb) | 31.4 kg (69 lb) |
| 1,000 kcal | 0.91 kg (2.0 lb) | 20.9 kg (46 lb) | 41.8 kg (92 lb) |
Calorie Deficit FAQ
- About 0.45 kg (1 lb) a week at first, by the 3,500-calorie rule. Over a year, Hall's NIH model expects about 10.5 kg (23 lb) rather than the 23.7 kg (52 lb) the rule implies, because your calorie needs fall as you lose weight.
- It is right for the first weeks and wrong for long-term predictions. It treats the deficit as fixed, but a lighter body burns less, so the same intake makes a smaller gap. The NIH Body Weight Planner, built on Hall's model, exists to correct exactly that.
- Enough for about 1 to 2 pounds (0.5–1 kg) a week, the CDC's guidance for steady, lasting loss — usually 500–1,000 kcal below TDEE for adults with weight to lose. Smaller deficits are easier to keep; very large ones are best supervised.
- Your TDEE fell as your weight fell, so the deficit you started with has shrunk, and intake often creeps up as well. Recalculate maintenance for your current weight and set a new target from that.
- Use the maintenance-calories calculator, which works it out from age, sex, weight, height and activity, or the BMR and TDEE pages in two steps. You can also measure it: eat a steady, logged intake for two to three weeks, and if your weight holds, that intake is your TDEE.