CalcKitWeight loss comes down to energy balance: when you consistently burn more calories than you eat, your body makes up the difference from stored fat. Because one kilogram of body fat holds approximately 7,700 kcal of energy, losing a full kilogram in a single week means building up a total deficit of about 7,700 kcal across those seven days — roughly 1,100 kcal per day.
The deficit formula
The math is simple:
Daily deficit = 7,700 ÷ (days you want to take to lose 1 kg)
For 1 kg per week: 7,700 ÷ 7 ≈ 1,100 kcal/day. For 1 kg in two weeks: 7,700 ÷ 14 ≈ 550 kcal/day. For 1 kg over ten days: 7,700 ÷ 10 ≈ 770 kcal/day. Pick a timeframe you can actually sustain — the best deficit is the one you can repeat for weeks.
Worked example
Say your maintenance calories — what you burn in a normal day — are 2,200 kcal (find yours with our free Calorie Calculator). A 1,100 kcal/day deficit would put your target at 1,100 kcal/day of food, which is uncomfortably low for most adults. A more workable split: eat 1,700 kcal (500 less than maintenance) and burn 600 kcal through brisk walking plus two gym sessions — total deficit 1,100 kcal/day without starving.
Splitting the deficit between diet and exercise
A pure-diet deficit feels miserable; a pure-exercise deficit eats your whole day. The practical approach is a mix. Aim for roughly 70% of your deficit from food (smaller portions, fewer sugary drinks, more protein to stay full) and 30% from movement (walking, cycling, strength training). Exercise also protects muscle mass while you lose fat, which diet-only weight loss does poorly.
A safer, steadier target
A 1,100 kcal daily deficit is aggressive: most nutrition guidelines recommend a 500–750 kcal/day deficit, which gives a steady 0.5–1 kg per week — the rate most experts consider safe and sustainable. At 500 kcal/day, the same 7,700 kcal formula gives you roughly 0.5 kg per week, which adds up to 2 kg a month without the hunger and fatigue of a crash diet. Slow loss also tends to preserve more muscle and is easier to keep off, because the eating habits behind it are habits you can actually live with.
Build your weekly deficit plan
Turn the formula into a concrete plan in five steps:
1. Find your maintenance calories. Run your age, height, weight and activity level through our free Calorie Calculator. This is your starting line — every deficit is measured against it.
2. Pick your pace. For 1 kg a week, subtract about 1,100 kcal/day from maintenance. For 0.5 kg a week, subtract about 550 kcal/day. Slower is fine — pick the number you can hold for a month without burning out.
3. Split diet and exercise. Don't take it all from food. For example, with maintenance at 2,200 kcal and a 1,100 target deficit: eat 1,500 kcal/day (700 below maintenance) and add 400 kcal/day of walking or gym time. Cutting food by 1,100 alone leaves you at 1,100 kcal of eating — too low for most adults.
4. Track the trend, not the day. Weigh yourself at the same time each morning and watch the weekly average. Water retention from salty meals or hard workouts can swing the scale by a kilogram overnight — the average is what tells the truth.
5. Recalculate after a few weeks. As you lose weight, your maintenance calories drop with you, quietly shrinking your deficit. Re-run the calculator every 3–4 weeks and adjust your target so progress continues.
Why the scale won't follow the math exactly
The 7,700 kcal figure is a rule of thumb, not a law. Early weeks can show faster drops (mostly water and glycogen, not fat), and later the body adapts — your maintenance calories quietly fall as you get lighter, shrinking your deficit unless you adjust. Salt, sleep, stress and hormones also shift water weight day to day. Judge your progress by the trend over 2–3 weeks, not by any single morning's number.