Calorie deficit calculator

A calorie deficit is eating fewer calories than your body uses in a day. Your body makes up the shortfall from stored energy, mostly body fat. Eating more than you use is a surplus, which is how weight is gained; matching it is maintenance.

Because energy balance is the fundamental rule of fat loss. As Andrew Huberman puts it, calories in versus calories out is the most important formula in weight management — no diet, fasting window or supplement works unless it ultimately creates a deficit. Knowing your number turns a vague goal into a daily target you can actually track.

It estimates how much energy you burn each day at your current size and activity level, then shows what a modest, sustainable reduction looks like. Use it to set a realistic starting point, then adjust every few weeks based on how your weight and energy respond.

A 15–20% deficit is a moderate starting point for most adults, and Rhonda Patrick notes that most caloric-restriction studies use around 20–30%. Larger deficits lose weight faster but are harder to sustain and can cost muscle as well as fat.

Somewhat. Research discussed by Peter Attia and Eric Ravussin shows the body adapts to restriction by burning a little less than expected. Keeping protein high, lifting weights and pairing diet with exercise limits this and preserves muscle.

The equation uses different constants for male and female bodies because average body composition differs. Choose the option that best matches your physiology.

Your practitioner may set a different target. Appetite and intake can change substantially on GLP-1 medications, so follow their guidance rather than a calculator.