Calorie Deficit Calculator

The calculator uses the Wishnofsky rule: 1 lb of body fat holds about 3,500 kcal, or 7,700 kcal per kg. It multiplies your target weekly loss rate by 7,700, then divides by 7 for a daily deficit. Subtracting that estimate from TDEE produces a planning target, not a personalized intake prescription.

It sits at the outer edge of what most guidelines consider sustainable. A 500 to 1,000 kcal daily deficit lines up with roughly 1 to 2 lb of loss per week, the standard recommended range. The calculator flags any daily deficit above 1,000 kcal as medically aggressive, because beyond that the risk of muscle loss, fatigue, gallstones, and rebound weight gain rises sharply.

The 1,200 kcal warning is a conservative software boundary, not a universal safety floor. Nutrient and energy needs vary with body size, age, sex, activity, health, and pregnancy. Very-low-calorie diets are generally below 800 kcal per day and require medical supervision. Ask a clinician or registered dietitian to review a low target rather than treating the warning as proof that a nearby value is safe.

Probably not exactly. The Wishnofsky rule is a flat, linear approximation, not a biological law. In practice your TDEE drops as you lose weight, water swings can mask fat loss for weeks at a time, and adherence to a deficit is rarely perfect. Treat the output as a starting estimate and recalculate every 4 to 6 weeks as your weight changes.

No. The calculator is an educational tool. It does not know your health history, medications, pregnancy status, training load, or eating-disorder history, all of which change what a safe deficit looks like for you. Talk to a registered dietitian or your doctor before starting a sustained calorie deficit, especially if you have a medical condition, are pregnant, or are under 18.