Every diet that has ever worked — keto, fasting, calorie counting — works for the same underlying reason: it puts you in a calorie deficit. Understanding the mechanism makes the whole thing far less mysterious.
TL;DR — Enter your maintenance calories, current and goal weight, and a timeframe in the calorie deficit calculator for a daily target.
What a deficit does
A calorie deficit means eating fewer calories than you burn. To cover the gap, your body draws on stored energy — mostly fat. About 7,700 calories equals roughly one kilogram of fat, so the size of your daily deficit sets the pace of loss. The calculator works backward from your goal and timeframe to the daily deficit it requires.
Setting a safe pace
Faster is not better. A loss of about 0.5–1% of body weight per week is the sustainable sweet spot. Push harder and you risk losing muscle, tanking your energy, and rebounding. The calculator flags when a target implies an aggressive pace or drops intake too low, so you can extend the timeline instead.
Keep it sustainable
A deficit you abandon in two weeks does nothing. Pair a moderate deficit with enough protein and some resistance training to protect muscle, and accept that the scale moves unevenly thanks to water and daily variation. Set a realistic plan in the calorie deficit calculator and give it time to work.