Calorie Deficit Calculator

A calorie deficit means eating fewer calories than you burn. Your body makes up the shortfall from stored fat — that is what weight loss is. Simple as it sounds, the deficit is usually the part people get right and the rate of loss that catches them out, so this page focuses on both the arithmetic and the realistic expectations around it.

Find your deficit

First, your maintenance calories (TDEE) come from your BMR and activity:

TDEE = BMR × activity factor

The BMR uses Mifflin-St Jeor:

Men:    10 × weight(kg) + 6.25 × height(cm) − 5 × age + 5
Women:  10 × weight(kg) + 6.25 × height(cm) − 5 × age − 161

The deficit and the math

Target intake = TDEE − deficit
Weekly loss = (deficit × 7) ÷ 7,700 kg

Since 1 kg of body fat ≈ 7,700 kcal, a 500 kcal daily deficit (3,500 kcal a week) loses about 0.45 kg per week — the classic sustainable pace. A 1,000 kcal deficit roughly doubles that. The 7,700 figure is itself an approximation of a rough rule: body fat contains energy at around 3,500 kcal per pound, a rule of thumb that has been quoted for decades because it is easy to remember and close enough for planning.

Example

A 30-year-old man, 175 cm, 75 kg, moderately active: TDEE ≈ 2,633 kcal. With a 500 kcal deficit → eat ≈ 2,133 kcal/day → ≈ 0.45 kg/week, so 5 kg in about 11 weeks.

A realistic view of the scale

Two things routinely surprise people starting a deficit. First, early weight loss is often much faster than the math predicts as the body sheds water and glycogen along with fat — a rapid drop in week one does not mean it will continue. Second, the rate slows over time: as you lose weight your maintenance falls, gently shrinking the same nominal deficit. Week-to-week fluctuations from water, salt and digestion can easily mask fat loss, so it is better to look at the trend over several weeks than to judge any single reading.

Sustainable vs aggressive

A smaller deficit (250–500 kcal) is easier to sustain, preserves more muscle and energy, and keeps you compliant long enough to actually reach your goal. Aggressive deficits strip weight faster but are harder to stick to, can drive hunger and fatigue, and increase the chance of losing lean tissue along with fat. If your goal is to keep muscle or you exercise regularly, lean towards the gentler end of the range.

Safety

Extremely low intake backfires — it is hard to sustain and risks muscle loss. This calculator never recommends going below 1,200 kcal per day. A deficit of 250–500 kcal is sustainable for most people. If you have an underlying health condition, are pregnant or are under medical care, seek professional advice before changing your diet — this content is general education, not medical advice.