Calorie Deficit / Surplus Calculator

Caloric deficit and surplus: the energy balance behind body composition

Energy balance is what you eat minus what you burn: Δ = kcal_intake − TDEE. TDEE (Total Daily Energy Expenditure) is the sum of your basal metabolic rate, the thermic effect of food, NEAT (non-exercise activity thermogenesis) and whatever you spend training. When Δ comes out negative you have a deficit and lose weight; when it is positive you have a surplus and gain. Wishnofsky's old 1958 shortcut puts 7700 kcal ≈ 1 kg of body fat, which is where the familiar “500 kcal/day gets you about half a kilo a week” figure comes from.

That linear math falls apart over the long haul, where it tends to overpredict how much you actually lose. The dynamic model from Hall et al. (2011, Lancet) explains why: as your mass comes down so does your TDEE (lower BMR, less NEAT, plus metabolic adaptation), and the weight-loss curve flattens out. If you are bulking lean, a surplus of 200–300 kcal/day keeps the muscle-to-fat ratio in your favor. Push past 500 kcal and you mostly add fat without any extra hypertrophy to show for it.

Applications

Cutting and bulking phases in bodybuilding, weight-loss protocols, contest prep periodization, making weight in combat sports, and clinical nutrition for obesity or sarcopenia. Coaches lean on the same math to work out how many weeks a prep needs before a photoshoot or competition.

FAQ

Is the 7700 kcal/kg rule exact? No. It is a rough shortcut. What you actually lose is a mix of fat, lean mass and water, and metabolic adaptation drags real loss below the prediction, which gets noticeable once you are past 12 weeks of dieting.

What is an ideal deficit? For most people, 10–25% below TDEE works well. Go beyond 30% and you start burning through muscle faster and suppressing hormones like leptin, T3 and testosterone.

Why don't I lose weight even in a deficit? Usually one of a few things: you are eating more than you think (untracked food), your TDEE estimate was too high, adaptive thermogenesis has kicked in, cortisol is holding water, or you simply haven't given it enough time. Recalculate every 3–4 weeks and adjust.