Calories in Body Fat Calculator

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Where 3,500 kcal per pound came from

Wishnofsky reviewed tissue-composition data and concluded that a pound of body-weight change was worth about 3,500 kcal. The paper is short, old, and still the constant every commercial diet uses. Per kilogram (divide 3,500 by 0.4536) the same figure is about 7,716 kcal. This site rounds to 7,700 so every tool matches.

The constant mixes fat, water and a little lean tissue. Pure triglyceride is closer to 9 kcal per gram, but you do not lose a kilogram of pure oil. You lose a mix. Treating 7,700 as 'the energy in fat' is already a planning shorthand.

If a page says 3,500 kcal per kilogram, it has the unit wrong by more than a factor of two. That error is how 'lose 10 kg in a month' arithmetic gets sold.

What Hall changed about the line

The Lancet 2011 paper by Hall and colleagues built a dynamic model in which resting metabolism, movement and the energy cost of tissue all change as weight changes. A static 3,500 kcal per pound projection over a year often lands near twice the loss the dynamic model predicts.

This calculator still prints the static line because people search for it, and because a four-week block is close enough that the dynamic correction is small. The honest sentence sits under the table: the last kilogram is slower.

The weight-loss time calculator applies the same constant after the calorie rails. Use that page when you want weeks that this site will actually plan, not an uncapped 750 kcal day.

Why the last kilogram is slower

Basal metabolism scales with mass. A smaller body burns less at rest. Non-exercise movement often falls in a deficit. The intake that produced a 500 kcal gap at 90 kg may produce a 350 kcal gap at 80 kg. Same fork, smaller fire.

Water and glycogen can hide a fortnight of fat loss after a salty meal or a hard training week. The table does not know about that. The check-in calculator compares expected kilograms from this constant with the scale.

Re-run TDEE every 4 to 6 weeks or after a 3% weight change. The deficit page will rebuild the daily target from the new mass.

How to read the deficit columns

The form always shows 250, 375, 500 and 750 kcal days plus the deficit you typed (100 to 1,500). Duplicates are dropped. Your row is marked. Days equal kilograms times 7,700 divided by that daily gap. Weeks are days divided by seven.

A 500 kcal gap is a common plan and is about 0.45 kg a week on this line. This site's live cut still refuses to go below 80% of TDEE or the sex-specific floor, so a 750 kcal ask on a small TDEE will not survive the rails.

Do not add tracker exercise on top of a TDEE that already has an activity factor. That double-count is how a 500 kcal 'gap' becomes a 200 kcal gap in real life.

Fat mass is not the same as scale mass

The recomposition calculator splits weight into fat mass and lean mass when you have two body-fat readings. This page assumes the kilograms you entered are the tissue you want to lose. If half of a past drop was water, the 7,700 line will look 'too pessimistic' next time.

Wishnofsky was writing about body-weight change, not dissected adipose tissue. That is another reason late weeks wander. Lean mass is expensive to keep and cheap to lose if protein and lifting disappear.

Keep protein at the cutting tier on the deficit and protein pages. The constant does not protect muscle. You do.

What to do with the weeks

Pick a deficit that still clears the rails on the deficit calculator. Then open the time calculator for weeks at 0.25, 0.5, 0.75 kg and the 1% cap. This table is the arithmetic lesson. Those pages are the plan.

If the weeks look short, the deficit is large or the kilogram figure is small. If they look endless, you asked for a 250 kcal gap on 8 kg, which is honest and slow.

Children and teenagers are out of scope on the energy tools that need adult TDEE. This table will still do the multiplication, but it is not a paediatric plan.

How it's calculated

Worked example: 5 kg at a 500 kcal daily deficit

1. Energy on the line = 5 × 7,700 = 38,500 kcal.
2. Days at 500 kcal/day = 38,500 ÷ 500 = 77 days (11.0 weeks).
3. The same 5 kg at 3,500 kcal/lb: 5 ÷ 0.4536 ≈ 11.02 lb, times 3,500 = 38,570 kcal, the same constant within rounding.
4. At 250 kcal/day the table doubles to 154 days. At 750 kcal/day it falls to 51 days, which this site may still refuse if 750 is more than 20% of TDEE.
5. After 3 kg are gone, re-estimate TDEE. The remaining 2 kg will need more than the original 31 days if expenditure has fallen.

Where this number is used in the real world

• Checking that 3,500 kcal is per pound, not per kilogram.
• Seeing days at 250, 500 and 750 kcal gaps side by side.
• Explaining why a crash-diet date will miss.
• Handing a chosen deficit to the time and deficit calculators.
• Comparing a check-in gap with this planning line.

Frequently asked questions

Keep going

A single number rarely tells the whole story. Alongside the energy in fat result, the weight-loss time calculator, the calorie deficit calculator, the check-in calculator and the TDEE calculator each add a different angle on the same measurements. For the reasoning behind the numbers, read How many calories to eat and Adaptation and plateaus.

Sources

1. Wishnofsky M. Caloric equivalents of gained or lost weight. Am J Clin Nutr 1958;6:542-6. doi.org/10.1093/ajcn/6.5.542
2. Hall KD, Sacks G, Chandramohan D, et al. Quantification of the effect of energy imbalance on bodyweight. Lancet 2011;378:826-37. doi.org/10.1016/S0140-6736(11)60812-X