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Nutrition

Calorie deficit calculator

The daily deficit needed to hit a goal weight by a given date — with a warning when the pace is too aggressive.

Your stats

Daily calorie deficit
625kcal / day

Subtract this from your TDEE to hit the goal in 16 weeks.

Weekly rate
1.25lb/wk
% bodyweight
0.63% / wk
Total loss
20.0lb

Estimated finish: Sep 15, 2026

What a calorie deficit does

A calorie deficit is the gap between what your body burns and what you eat. Sustain it for long enough and your body makes up the difference from stored energy — mostly fat, with some glycogen, water, and a small amount of lean tissue. That is the basis of every diet that has ever worked.

The size of the deficit determines how fast you lose, and how comfortable the process is. Small deficits (250–500 kcal) are easier to maintain and protect muscle better. Larger deficits (700+ kcal) lose weight faster but tend to cost more in hunger, training quality, and lean mass.

How the deficit is calculated

total loss(lb)      = current weight − goal weight
weekly rate(lb/wk)  = total loss / weeks
daily deficit(kcal) = weekly rate × 3,500 / 7

The conversion uses 3,500 kcal per pound of fat. The calculator flags any plan that exceeds 1 % of bodyweight loss per week, and flags more strongly above 1.5 %.

Frequently asked questions

How much weight can I safely lose per week?
The widely-cited safe ceiling is about 1 % of bodyweight per week. Above that, the share of weight loss that comes from muscle rather than fat increases sharply, and training quality starts to drop. For a 200 lb person that ceiling is roughly 2 lb per week; for 150 lb, about 1.5 lb. Going slower than 0.5 % per week is also fine — and tends to be easier to stick to.
Why 3,500 calories per pound?
The figure comes from the approximate energy density of body fat — about 3,500 kcal per pound, or 7,700 kcal per kilogram. It's a simplification; real-world weight loss includes water, glycogen, and a little muscle, and metabolic adaptation slightly reduces the deficit over time. But for setting an initial target, the 3,500 rule of thumb is close enough.
What if my weight stalls?
Two common causes. First, metabolic adaptation: as you get lighter, you burn fewer calories doing the same things. After 8–12 weeks of dieting, your true deficit may have shrunk by 100–200 kcal even though your food intake hasn't changed. Second, fluid retention from glycogen, sodium, or stress can mask fat loss on the scale for one to three weeks at a time. Track a four-week trend rather than reacting to any single weigh-in.
Should I take diet breaks?
Yes, eventually. After 8–12 weeks of an aggressive deficit, taking 1–2 weeks at maintenance calories helps restore hormones, training capacity, and adherence. The MATADOR study showed intermittent dieting outperformed continuous dieting for fat loss over a longer period.
Will I lose muscle in a deficit?
Some, almost always. To minimise it, keep the deficit modest (under 1 % bodyweight per week), eat at least 0.8–1.0 g of protein per pound, and keep lifting heavy. Cardio is fine but should not replace resistance training during a cut.

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