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About this tool
The daily calorie deficit needed to reach a goal weight by a target date.
The Calorie Deficit Calculator converts a weight-loss goal and a deadline into the daily calorie deficit it implies, using the standard approximation that one kilogram of body fat stores about 7,700 kcal: daily deficit = kg to lose × 7,700 ÷ (weeks × 7). Enter your current weight, target weight and the number of weeks, and it returns the deficit per day alongside the weekly loss rate that deficit represents. Seeing both together is the point — a target that needs 1,200 kcal a day off is telling you the deadline is wrong, not that you need more willpower.
Open Calorie Deficit Calculator on AltFTool — it loads instantly in your browser.
Enter your current weight in kilograms to establish a baseline for your weight loss journey
Input your goal weight in kilograms to determine the total weight you aim to lose
Specify the number of weeks you have to reach your goal weight, allowing the calculator to compute the necessary daily calorie deficit
Instead of a vague goal, you get the exact per-day shortfall the timeline demands, which is the figure you can act on at meals.
The weekly loss rate is shown next to the deficit, so a plan that needs 1.5 kg a week is obvious before you start it rather than three weeks in.
The whole calculation rests on the 7,700 kcal-per-kg figure, stated openly, so you know exactly what assumption the answer depends on.
About 733 kcal per day. That comes from 8 kg × 7,700 kcal ÷ 84 days, and it works out to roughly 0.67 kg of loss per week. Stretch the same 8 kg over 20 weeks and the daily deficit drops to about 440 kcal.
Roughly 7,700 kcal, which is the constant this tool uses (the imperial equivalent is about 3,500 kcal per pound). It is an approximation based on the energy density of adipose tissue, and real losses include water and some lean mass, so early weeks often move faster than the maths predicts and later weeks slower.
Deficits beyond roughly 1,000 kcal a day, or loss faster than about 1% of body weight per week, are generally where sustainability and nutrient adequacy start to suffer. If the calculator returns a figure in that range, lengthening the timeline is usually the better fix. Anyone considering an aggressive cut should discuss it with a doctor or dietitian first.
Because the deficit is measured against maintenance, and maintenance falls as you lose weight — a lighter body burns less at rest and in movement. Recalculate your maintenance every 4-5 kg, and remember day-to-day scale swings of 1-2 kg from water, salt and glycogen can hide real fat loss for a week or more.
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