How is weight loss estimated from a calorie deficit?

This tool uses the widely cited approximation that roughly 7,700 kcal of sustained deficit corresponds to about 1 kg of fat loss (about 3,500 kcal per pound). It is an average, not a precise conversion — water weight and metabolic adaptation make real-world loss uneven week to week.

What deficit size should I use?

A 500 kcal/day deficit (about 0.45 kg/week) is the standard moderate target used in most clinical and coaching guidance. A 750 kcal/day deficit is more aggressive and harder to sustain; anything larger risks excessive muscle loss and is not modeled here.

Why does the timeline show a straight line instead of the real bumps in my weight?

The timeline is a projection assuming a constant deficit and constant metabolic rate. In reality, water retention, sodium intake, hormonal cycles and adaptive drops in TDEE as you lose weight all cause real weigh-ins to zig-zag around this line — trust the multi-week trend, not any single day.

Is there a minimum calorie target I shouldn't go below?

Most guidelines caution against sustained intakes below about 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. If your target from an aggressive deficit falls near or below that, use a smaller deficit instead.

Calorie Deficit Calculator

Turn a daily calorie deficit into a target intake and a week-by-week weight-loss timeline, based on the standard 7,700 kcal-per-kg-of-fat estimate.

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Formula: Weekly loss (kg) = daily deficit × 7 ÷ 7,700; projected weight = current weight − (weekly loss × week number)

Worked examples

80 kg, 2,700 kcal maintenance, moderate 500 kcal deficit, 12 weeks
A moderate 500 kcal/day deficit, the classic 'lose about 0.45 kg (1 lb) a week' target, projected over a 12-week block.
65 kg, 2,000 kcal maintenance, aggressive 750 kcal deficit, 8 weeks
An aggressive deficit pushes this person's target near the 1,200 kcal floor most guidelines flag as a minimum without supervision.
100 kg, 3,200 kcal maintenance, small 250 kcal deficit, 24 weeks
A small, sustainable deficit over a longer 24-week block for someone who wants a slower, easier-to-maintain rate of loss.

What this calculator estimates

A calorie deficit is simply eating less energy than your body uses in a day. This tool turns a chosen daily deficit into a concrete calorie target and projects, week by week, how much weight that deficit is likely to remove over time — so you can see the trade-off between an aggressive cut and a slower, easier one before you start.

How the math works

It uses the widely cited approximation that roughly 7,700 kcal of sustained deficit corresponds to about 1 kg of fat loss (about 3,500 kcal per pound, the figure most US sources use). Multiplying your daily deficit by 7 gives a weekly deficit; dividing that by 7,700 gives an expected weekly loss in kilograms. The timeline table then simply subtracts that weekly amount from your current weight, one row per week, for however many weeks you ask for.

Choosing a deficit size

A 500 kcal/day deficit — a "moderate cut" — is the standard target used across most clinical and coaching guidance and corresponds to roughly 0.45 kg (1 lb) lost per week. A 750 kcal/day deficit is more aggressive: faster on paper, but harder to sustain and more likely to cost muscle along with fat, especially for people who don't have much excess weight to lose. Smaller deficits (200–300 kcal) are slower but easier to stick to for longer, which often matters more for actual results than the theoretical speed of a bigger one.

How to use the result

Treat the calorie target as your starting point and the timeline as a rough guide, not a guarantee. Weigh yourself under similar conditions (same time of day, similar clothing) most mornings and track the trend over 1–2 weeks rather than reacting to any single day — water retention, sodium, hormonal cycles and digestion routinely swing daily weight by a kilogram or more in either direction, which is exactly why the projection line looks smoother than real life will. If your actual trend runs noticeably faster or slower than the projection after two to three weeks, adjust the deficit by 100–200 kcal rather than assuming the formula is broken.

Limits

The 7,700 kcal/kg figure is a population average, not a fixed physical law — actual energy cost per kilogram of tissue lost varies with how much of that loss is fat versus water versus muscle, and your metabolism typically slows somewhat as you lose weight, which this simple linear projection doesn't model. Do not sustain intakes below about 1,200 kcal/day (women) or 1,500 kcal/day (men) without medical supervision; if your deficit target falls near or under that floor, choose a smaller daily deficit instead. This tool gives a general estimate and is not medical advice.

Frequently asked questions

How is weight loss estimated from a calorie deficit?: This tool uses the widely cited approximation that roughly 7,700 kcal of sustained deficit corresponds to about 1 kg of fat loss (about 3,500 kcal per pound). It is an average, not a precise conversion — water weight and metabolic adaptation make real-world loss uneven week to week.
What deficit size should I use?: A 500 kcal/day deficit (about 0.45 kg/week) is the standard moderate target used in most clinical and coaching guidance. A 750 kcal/day deficit is more aggressive and harder to sustain; anything larger risks excessive muscle loss and is not modeled here.
Why does the timeline show a straight line instead of the real bumps in my weight?: The timeline is a projection assuming a constant deficit and constant metabolic rate. In reality, water retention, sodium intake, hormonal cycles and adaptive drops in TDEE as you lose weight all cause real weigh-ins to zig-zag around this line — trust the multi-week trend, not any single day.
Is there a minimum calorie target I shouldn't go below?: Most guidelines caution against sustained intakes below about 1,200 kcal/day for women or 1,500 kcal/day for men without medical supervision. If your target from an aggressive deficit falls near or below that, use a smaller deficit instead.

These calculators give general estimates from published formulas. They are not medical advice and do not account for your individual health; talk to a qualified professional before changing your diet or training.