How big should a calorie deficit be?

Percentages beat a flat 500

Five hundred calories is a rounding error at 3,000 maintenance and a brutal cut at 1,600. A calorie deficit should scale with the person. Ten percent of 2,400 is 240; twenty percent is 480. Same person, two different lives.

The calorie deficit calculator does this in one screen. This page is the decision, not the arithmetic.

What the bands actually feel like

These are descriptions, not prescriptions.

• 10% — social meals still fit. Progress is slow enough that people quit from boredom, not hunger.
• 15–20% — the default. Visible on a monthly average, compatible with training if protein and sleep are not an afterthought.
• 25%+ — faster on paper, hungrier, more lean-tissue risk, harder to log honestly. Reasonable as a short block with an end date.
• As a rate, 0.5–1% of body weight per week is the same idea in different units.

A worked example

Maintenance measured at 2,200. A 15% deficit is 1,870 kcal. Over a week that is 2,310 kcal of gap. The 3,500-calorie rule converts that toward two-thirds of a pound and overstates the months ahead: expenditure falls as mass falls. Expect the rate to slow. That is adaptive thermogenesis plus simple physics, not failure.

When the number is too small on the plate

If twenty percent lands you on an intake you cannot build three meals from, the cut is too large for your maintenance — or the maintenance was a lie. Raise intake toward a holdable target rather than “discipline” a number that guarantees a binge. A diet break is a legitimate next step.

Do not use this guide to set a target if you are pregnant or breastfeeding, under 18, already at or below a healthy weight, or if you have a history of disordered eating. The NIMH overview of eating disorders is the page to read instead of another calculator.

Stalls are usually not a size problem

Three quiet weeks of a flat average, after you have checked logging and water, is when you might shrink the gap by 100–150 calories — or take a break. One heavy morning is not a stall. Eating back watch calories is the most common way a correctly sized deficit becomes maintenance with extra steps.

Hall’s energy-imbalance work is why the same percentage produces less loss as you get smaller. Recalculate maintenance after about 5 kg. Do not double the cut because a calendar app was rude.

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