Calorie deficit calculator

Using the calculator

Enter your estimated maintenance calories — from the TDEE calculator, or better, from your own logged data. Choose a deficit size. The tool returns a daily calorie target and the weekly energy shortfall it implies.

A deficit is expressed as a percentage rather than a flat number on purpose. Two hundred calories is a rounding error for a 3,000-calorie maintenance and a serious cut at 1,600. Percentages scale with the person.

Choosing a deficit size

Larger deficits lose weight faster on paper and fail more often in practice, because the thing that determines your result over months is whether you can keep doing it.

• Gentle (10%) — barely noticeable day to day, holds through social events and bad weeks. The default choice if you have more than a few months to work with.
• Moderate (15–20%) — the standard recommendation. Visible progress, still compatible with training and normal life.
• Aggressive (25%+) — faster, hungrier, harder to sustain, and more of the loss tends to come from somewhere other than fat. Reasonable only for short, deliberate blocks.
• As a rate rather than a percentage, roughly 0.5–1% of body weight per week suits most people. Above that, adherence and training quality usually suffer first.

A worked example

Say the TDEE calculator put your maintenance at 2,400 calories and you pick a 20% deficit.

Daily target: 2,400 − (0.20 × 2,400) = 1,920 calories. Weekly shortfall: 480 × 7 = 3,360 calories.

The old rule of thumb converts that to about a pound a week, on the assumption that a pound of fat is 3,500 calories. Real bodies do not behave that linearly — see the next section.

Why the "3,500 calories = 1 pound" rule overpromises

The 3,500-calorie rule assumes your expenditure stays fixed while your weight falls. It does not. A lighter body burns less at rest and costs less to move, so the same intake that produced a 500-calorie deficit in month one produces a smaller one by month four. The rule therefore overestimates long-run weight loss, sometimes badly.

Research modelling this dynamic gives a more realistic rule of thumb: a sustained change of about 10 calories a day leads to roughly a pound of eventual weight change, with about half of that arriving within a year and most of it within three. Slower than the linear rule promises, and it keeps going for longer.

The practical consequence: expect weight loss to decelerate even when your adherence is perfect. That is physiology working as designed, not failure. The NIH Body Weight Planner models this properly if you want a projection that accounts for it, and the deficit guide walks through what it feels like month to month.

What to do when the scale stalls

Genuine plateaus and apparent plateaus look identical for the first two weeks. Work through this order before cutting calories again.

• Check the timescale. Under two weeks of a flat 7-day average is not a plateau — water retention routinely masks fat loss for that long.
• Check the logging. Intake drift is the usual culprit: untracked oil, drinks, tastes while cooking, generous portion estimates. Weigh food for a week and compare.
• Check your weight change since you started. Down 6 kg? Your maintenance has fallen with you and the target needs recalculating.
• Check the rest of your movement. Deficits quietly reduce spontaneous activity — you fidget less, walk less, take the lift. A step target defends against this better than another calorie cut.
• Only then adjust intake, and by 100–150 calories, not 500. Or take two weeks at maintenance and restart — a break is a legitimate tool, not a failure.

When a deficit is the wrong tool

A calculator cannot see you, so it will happily produce a number that is wrong for your situation. Do not run a deficit from this tool if you are pregnant or breastfeeding, if you are under 18, if you are already at or below a healthy weight for your height, or if you have any history of disordered eating — restriction targets can be actively harmful there.

If you are managing diabetes, thyroid conditions, or taking medication that affects appetite or metabolism, the arithmetic still applies but the plan should be made with a clinician who knows your history.

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