Daily deficit (kcal)

Weight-loss goal (lb)

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General estimate for planning only — not medical advice. Consult a doctor about your specific situation.

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Weekly weight loss rate by daily calorie deficit — Halve the 500 kcal deficit and the timeline doubles.

Method & verification

How This Tool Works

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Calculation Method

Rate = Daily deficit × 7 ÷ 3500

Site methodology

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Assumptions to Verify

These tools provide general estimates for planning and education only.
They are not medical advice and not a substitute for a qualified healthcare professional.
Always consult your doctor or another healthcare provider about your specific situation.

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Worked example: 500 kcal/day to lose 15 lb

Take the most common setup: a 500 kcal daily deficit and a 15 lb goal. A pound of body fat holds roughly 3,500 kcal of energy, so the weekly math is 500 x 7 = 3,500 kcal, which is exactly one pound per week. At that rate, 15 lb takes 15 / 1.0 = 15 weeks, or about three and a half months.

Change one input and the plan shifts fast. A 750 kcal deficit gives 750 x 7 / 3,500 = 1.5 lb/week, so 15 lb lands in 10 weeks. A gentler 250 kcal deficit gives 0.5 lb/week and needs 30 weeks. Halve the daily cut and you double the timeline; that trade is the whole decision. The calculator does the same division every time, so the only judgment call is which rate fits your appetite and schedule.

One check worth running by hand: a 300 kcal deficit toward a 12 lb goal. Weekly rate is 300 x 7 / 3,500 = 0.6 lb, and 12 / 0.6 = 20 weeks. If the tool shows 20 weeks, the math path is confirmed.

Where the flat 3,500 rule breaks down

The 3,500 kcal-per-pound figure assumes all lost weight is fat, but real loss is 70 to 80 percent fat and the rest water, glycogen, and some lean tissue, especially in the first two weeks. A 1,000 kcal deficit often shows 3 to 4 lb lost in week one, then 1 to 2 lb per week after. The early number is water; do not adjust the deficit because of it.

Your energy needs also drop as you shrink. A 200 lb person cutting 500 kcal burns fewer total calories at 180 lb, so a deficit fixed at 500 kcal on day one might be closer to 350 kcal effective by month three, stretching a 15-week plan toward 18 or 19 weeks. The 0.5 to 1 percent body weight per week guideline (roughly 1 to 2 lb at 200 lb) exists because it stays sustainable as the floor moves.

Diet breaks can help accuracy more than they hurt speed: research on two-weeks-on, two-weeks-off dieting showed equal total fat loss to continuous dieting over 30 weeks, with less lean tissue lost. Recalculate your deficit every 5 to 10 lb of change rather than trusting one entry for the whole run.