CalcVitalsCalorie Deficit Calculator — When Do You Reach Your Goal?
A kilogram of body weight holds about 7,700 kcal, so the maths of a diet is division: at a 500 kcal daily deficit, losing 10 kg takes about 154 days — roughly five months. Enter your own numbers and this page dates it exactly.
How it works
This is the simplest useful model in weight management: the gap between where you are and where you want to be, expressed in kilocalories, divided by the daily gap you can sustain. It ignores almost everything complicated — and still lands most people within a few weeks of reality, which is more than can be said for most diet advertising.
Two forces bend the straight line. The first is water: glycogen stores, salt, hormones and digestion all move body water by a kilogram or more, so the scale will regularly deny a week of genuine fat loss and then concede two weeks' worth overnight. The second is adaptation: as you lose weight your maintenance calories drop, so a deficit fixed at the start is quietly smaller by the end. Serious projections shrink the deficit as the weight falls; this page keeps the simple version and tells you to allow grace.
The comparison rows are there to make a point about sustainability. Doubling the deficit does not quite halve the time — adherence falls off a cliff as deficits grow — and the plan you can still be following in month four beats the heroic one abandoned in week three, every time.
The method
Energy gap = (current − goal) kg × 7,700 kcal/kg. Days = gap ÷ daily deficit, rounded up; the date counts from today. Alternative-deficit rows use the same gap. The model holds the deficit constant; real-world maintenance falls roughly 20–30 kcal per kilogram lost.
Frequently asked questions
What is a sensible daily deficit?
For most people 300–600 kcal/day: large enough to see steady progress, small enough to keep hunger, training and mood intact. Deficits above 750 kcal/day are best run with professional guidance.
Why has my weight loss stalled at the same deficit?
Usually a mix of water retention masking fat loss, quiet reductions in daily movement as you get lighter, and tracking drift. If three honest weeks show no trend, trim another 100–200 kcal or add movement.
Is 7,700 kcal per kilogram exact?
It is the well-measured average energy density of adipose tissue. Individual tissue composition varies slightly, and early diet weight includes water and glycogen — one reason the first week always over-delivers.