How the timeline is calculated
One kilogram of body fat stores roughly 7,700 kcal of energy. Dividing the total weight you need to lose by your daily calorie deficit gives the number of days it should take at a steady rate.
- current — current weight (kg)
- target — goal weight (kg)
- deficit — daily calorie deficit (kcal)
- 7,700 — kcal stored per kg of body fat
More detail
Why 7,700 kcal per kilogram
This figure comes from Wishnofsky's 1958 estimate of the energy density of body fat loss and is the standard reference used in most calorie-deficit calculators. It assumes the deficit is met consistently every day, with no other changes.
Bigger deficits aren't always faster in practice
The math scales linearly, but very large deficits (over ~1,000 kcal/day) are hard to sustain and tend to cost more muscle. A deficit of 300–500 kcal/day is a common target for a pace that's realistic to keep up.
Practical tip. Treat the result as a floor, not a guarantee — weight loss slows as your body adapts. Re-check your progress every 2–3 weeks and adjust the deficit if the scale isn't moving.
Frequently asked questions
How long does it take to lose 10kg with a 500 kcal daily deficit?
10kg × 7,700 kcal/kg = 77,000 kcal total, divided by 500 kcal/day ≈ 154 days, or about 22 weeks. Enter your own numbers above to get an exact figure.
Why does the calculator use 7,700 kcal per kilogram?
That's Wishnofsky's widely cited estimate for the energy density of a kilogram of body fat lost, and it's the standard figure used to convert a calorie deficit into an expected timeline.
Why does the result show "—" for some inputs?
That happens if the current weight isn't greater than the goal weight (nothing to lose), or if the daily deficit is 0 or negative — the formula divides by the deficit, so it can't compute a timeline.
Does a bigger daily deficit always mean faster results?
Mathematically yes — the formula is linear, so doubling the deficit halves the days. In practice, deficits above roughly 1,000 kcal/day are hard to sustain and increase muscle loss, so most guidance favors 300–500 kcal/day instead.
Is this timeline guaranteed?
No. It's a simplified estimate assuming a constant daily deficit; actual results vary with metabolic adaptation, water weight, and how consistently the deficit is held. Use it as a planning starting point, not a guarantee.