How to Set a Calorie Deficit That Holds

Quick Answer

A calorie deficit is the gap between what your body burns in a day and what you eat. This weight loss calorie calculator estimates your maintenance calories from a Mifflin-St Jeor basal metabolic rate scaled by activity, then subtracts the gap your chosen weight loss rate needs. Where the 7,700 kcal per kilogram figure comes from is body fat itself: roughly that much energy is stored in a kilogram of it, so losing half a kilogram a week takes a deficit of about 550 calories a day. The daily calorie target is floored at your BMR, so an aggressive rate never produces a number you should not eat, which makes this a quick way of checking whether an app-suggested target is dangerously low. Enter a goal weight and the timeline answers how long it will take me to lose weight at the rate I picked.

How a Calorie Deficit Works

Energy balance is the whole mechanism. Eat less than you burn and your body makes up the difference from stored energy, mostly fat; eat more and it stores the surplus. The size of the gap sets the rate. The calculator works backwards from the rate you want: it converts your weekly target into a daily energy shortfall, subtracts that from maintenance calories, and gives you the number to eat. Everything upstream of that is an estimate, which is why the tool shows maintenance, the deficit, and the resting floor side by side rather than a single figure to obey.

Choosing a Rate of Loss

How fast weight loss can safely go has a well-supported answer: 0.5 to 1 percent of body weight a week. At 80 kg that is 0.4 to 0.8 kg, needing a deficit of roughly 440 to 880 calories a day, which is what the calories to lose weight at that rate work out to. Read as a weight loss calculator or as a cutting calorie calculator, the arithmetic is the same. A gentle deficit versus an aggressive one is the only real choice on this page, and slower is not weaker: gentle deficits preserve muscle better, leave enough energy to train hard, and survive a bad week without collapsing. Aggressive rates lose more lean tissue, and the practical failure mode is not danger but abandonment, usually inside a fortnight. Pick the rate you could still be running in two months.

Why the Target Moves

A lighter body is cheaper to run. Lose 5 kg and your maintenance falls by roughly 50 to 100 calories a day, which quietly narrows the deficit you set at the start. Metabolic adaptation shrinks it a little further, as the body trims non-exercise movement and resting expenditure in response to sustained energy shortage. Neither effect is dramatic, and neither is a broken metabolism, but together they explain most stalls at week eight or ten.

Examples

Man, 30, 90 kg, 180 cm, moderately active, 0.5 kg a week. For example, maintenance lands near 2,900 calories, so the target is about 2,350 with a deficit of 550.

The same man asking for 1 kg a week. For example, the deficit would be 1,100, putting intake near 1,800, which is above his BMR of about 1,800 but leaves almost no margin.

Woman, 35, 65 kg, 165 cm, lightly active, 1 kg a week. For example, maintenance is near 1,900, so a 1,100 deficit would fall below her BMR of about 1,350; the target holds at the floor and the achievable rate drops to roughly 0.5 kg a week.

Common Mistakes